SUBSURFACE FACIES ANALYSIS OF THE CLINTON SANDSTONE, LOCATED IN PERRY, FAIRFIELD, AND VINTON COUNTIES
Craig Allen Stouten
A Thesis
Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
December 2014
Committee:
James Evans, Advisor
Charles Onasch
Jeff Snyder
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ABSTRACT
James Evans, Advisor
This paper focuses on the depositional environment of the “Clinton Sandstone” located in
Perry, Fairfield, and Vinton Counties in central and southeastern Ohio. Core from wells
numbered 2866, 2941, 2942, 2943, 2965, and 2980 were accessed from the Ohio Geological
Survey, H.R. Collins Core Laboratory. Each core was described, photographed, and sampled for
thin sections and lithofacies analysis. In addition, gamma-ray and neutron density logs were
acquired for each well. The geophysical logs were used for litho-correlation and to examine 3-D
architecture. This new data was used to re-evaluate the depositional interpretations.
The “Clinton Sandstone” is an informal name given to the Lower Silurian sandstone unit that stratigraphically lies between the Cabot Head Shale and the Neagha Shale in southeastern Ohio.
The “Clinton Sandstone” correlates with the Tuscarora Sandstone in Pennsylvania and West
Virginia. Confusingly, the “Clinton Sandstone” is not related to the Upper Silurian Clinton
Group located in western New York. Previous workers have interpreted the “Clinton Sandstone” to be part of a wide range of environments, from fluvial-deltaic to a strand plain, and incorporating tidal channels, delta plains, crevasse-splays, and offshore marine deposits. This study confirms some, but not all of the previous interpretations, finding the “Clinton Sandstone” to be part of a delta plain, delta front, and prodelta environment.
There are a total of 16 lithofacies observed from the six cores studied. The dominant lithofacies are composed of sandstone, and include massive bedding, cross-bedding, planar lamination, shale partings (mud drapes), and mud intraclasts. There are also heterolithic sandstone-mudstone or siltstone-mudstone intervals with lenticular bedding, wavy bedding, and flaser bedding. Secondary features include ball-and-pillow structures. Mudstone is readily iii
available and most of it is represented as mud drapes or thin intervals separating sandstone packages, or as mud intraclasts in sandstone. However, there are several large sections within the cores studied that contain around 1 m or more continuous mudstone. There are also thin 3 - 6 cm limestone intervals. These only appear toward the bottom in wells 2942 and 2943. These limestone packages are massive, and contain brachiopod fragments and bryozoans.
These well samples show a strong tidal influence. Mud chips, mud drapes, and various shale partings are all negative factors that can lead to reservoir compartmentalization. Other features found that may contribute to poor reservoir quality are the tight nature of the grains, which contribute to low porosity and permeability. Quartz overgrowths are also present in these samples and have the potential to further hinder fluid flow as well as decrease the size and amount of pore space present.
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This thesis is dedicated to my mother and father who have supported me throughout all of my endeavors. I would not be half the person I am today without their countless sacrifices.
I would also like to dedicate this thesis to my late friend Dustin Cole Knapp. You will never be forgotten.
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ACKNOWLEDGEMENTS
I would like to begin by thanking my mother, Toni, and my father, Bruce, for all their support, encouragement, and help financially throughout my entire college career.
I would also like to thank my advisor, Dr. James Evans, for all his guidance, insight, and willingness to help with all aspects of this thesis. I would also like to thank the remainder of my committee, Dr. Charles Onasch and Dr. Jeffery Snyder for their assistance and taking time out of their busy schedules to be on my committee.
I want to thank the Ohio Geological Survey, especially Gregory Schumacher and Aaron
Evelsizor, for access to the core facility, retrieving specified samples from the cores, and assisting me with finding the appropriate geophysical logs.
I would also like to thank Bob Taylor Engineering, Inc., including Bob Taylor and Linda
Taylor for the opportunity to work for such a reputable company and for being very flexible with my limited availability to work only during summer months and occasional winter breaks.
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TABLE OF CONTENTS
Page
INTRODUCTION………………………………………………………………… 1
“Clinton Sandstone”………………………………………………………. 1
Depositional Environments………………………………………………. 2
Deltas……………………………………………………………... 2
Barrier Islands……………………………………………………. 7
Offshore Environment…………………………………………… 7
Offshore Transition Zone……………………………………….. 8
Shoreface Zone…………………………………………………. 8
Foreshore (Beachface) Zone…………………………………… 13
Lagoons…………………………………………………………... 13
Estuaries………………………………………………………….. 14
Tidal Flats………………………………………………………… 17
Purpose and Goals………………………………………………………. 21
GEOLOGIC BACKGROUND…………………………………………………… 23
Geological Setting…………….…………………………………………. 23
Regional Stratigraphy…………………………………………………….. 27
Cabot Head Shale………………………………………………… 27
Neagha Shale…………………………………………………….. 29
Packer Shell Limestone or Brassfield Limestone………………… 30
“Clinton Sandstone”……………………………………………………… 30
Stratigraphy and Age ……………………………………………. 30 vii
Lithology…………………………………………………………. 33
Depositional Environment ………………………………………. 34
Petroleum Geology………………………………………………. 37
METHODS…………………………………………………………………… 40
Field Methods……………………………………………………………. 40
Diamond Drill Cores…………………………………………….. 40
Geophysical Log Analysis……………………………………….. 43
Laboratory Methods……………………………………………………… 44
Thin Section Analysis……………………………………………. 44
Analytical Methods……………………………………………………….. 44
Isopach Map………………………………………………………. 44
RESULTS…………………………………………………………………………. 48
Well Stratigraphy………………………………………………………….. 48
Well 2866…………………………………………………………. 48
Well 2941…………………………………………………………. 48
Well 2942…………………………………………………………. 49
Well 2943…………………………………………………………. 49
Well 2980…………………………………………………………. 50
Well 2965…………………………………………………………. 50
Lithology…………………………………………………………………… 63
Sandstone…………………………………………………………. 63
Siltstone…………………………………………………………… 63
Limestone…………………………………………………………. 63 viii
Mudstone………………………………………………………….. 66
Lithofacies Analysis………………………………………………………. 66
Planar-Tabular Cross-bedded Sandstone (Lithofacies Sc)…….… 71
Trough Cross-bedded Sandstone With Shale Partings (Lithofacies Sth)……………………………………………………. 71
Massive Sandstone With Mudstone (Lithofacies Smi)……………. 73
Massive Sandstone (Lithofacies Sm)……………………………. 73
Laminated Sandstone (Lithofacies Sl)…………………………… 75
Laminated Siltston (Lithofacies SSl)……………………………. 75
Heterolithic Lenticular Bedded Sandstone-Mudstone (Lithofacies SMk)………………………………………………… 77
Heterolithic Flaser Bedded Sandstone-Mudstone (Lithofacies SMf)………………………………………………… 77
Heterolithic Bedding With Wavy Bedding (Lithofacies SMw)… 79
Heterolithic Bedding With Ball-And-Pillow Structure (Lithofacies SMd)………………………………………………… 79
Heterolithic Laminated Sandstone-Mudstone (Lithofacies SMl).. 81
Heterolithic Laminated Siltstone-Mudstone (SSMl)…………….. 81
Heterolithic Siltstone-Mudstone With Bioturbation (Lithofacies SSMb)……………………………………………….. 83
Massive Mudstone With Bioturbation (Lithofacies Mmb)……… 85
Massive Mudstone (Lithofacies Mm)…………………………… 85
Massive Limestone (Lithofacies Lm)……………………………. 87
Lithofacies Assemblages…………………………………………………. 87
Tidal Inlet Channel……………………………………………….. 88
Tidalites…………………………………………………………… 88 ix
Distributary Mouth Bars…………………………………………. 91
Point Bar Sequence………………………………………………. 94
Trace Fossils………………………………………………………………. 94
Core Logs Correlating to Geophysical Logs……………………………… 98
Well 2866………………………………………………………….. 98
Well 2941………………………………………………………….. 98
Well 2943…………………………………………………………. 99
Well 2980…………………………………………………………. 100
Basin Mapping…..………………………………………………………… 105
Litho-correlation Profiles…………………………………………. 105
Northwest-Southeast Profile………………………………………. 105
Northeast-Southwest Profile………………………………………. 106
Isopach Map………………………………………………………. 106
3-D Subsurface Wireframe Map………………………………….. 110
Reservoir Compartmentalization………………………………………….. 115
Micro-Scale………………………………………………………. 115
Meso-Scale……………………………………………………….. 116
Macro-Scale……………………………………………………… 117
DISCUSSION…………………………………………………………………….. 120
Depositional Environments……………………………………………….. 120
Tide Dominated Deltas…………..………………………………… 120
Meander Point Bar………………………………………………… 121
Interdistributary Bays…………………………………………….. 121 x
Distributary Channels…………………………………………….. 122
Distributary Mouth Bars………………………………………….. 122
Prodelta…………………………………………………………… 122
Similarities With Previous Works………………………………………… 123
Petroleum Geology………………………………………………………... 124
SUMMARY & CONCLUSIONS………………………………………………… 128
REFERENCES……………………………………………………………………. 130
APPENDIX A: GEOPHYSICAL LOGS…………………………………………. 141
APPENDIX B: CORE LOGS…………………………………………………….. 154
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LIST OF FIGURES
Figure Page
1 Diagram of a delta complex……………………………………………… 3
2 Stratigraphic section of a barrier island complex………………………. 9
3 Typical tempestite sequence…………………………………..………… 10
4 Diagram of an offshore to a foreshore environment……………………. 11
5 Stratigraphic section of a lagoon within a barrier island complex …….. 15
6 Diagram of a tidal flat environment…………………………………...... 18
7 Diagram showing flaser, wavy, and lenticular bedding………………... 20
8 Geological map of Ohio ………………………………………….…….. 24
9 Paleogeographic map for (how the continents were arranged during) the Silurian period ………………………………………………. 25
10 Lithology map of Ohio………………………………………………...... 26
11 Map of the Appalachian basin …………………………………………… 28
12 Map of wells drilled in Ohio …………………………..…………………. 39
13 Map of the study area ……………………………………………………. 41
14 Well log of well 2866 (-758 m to -760 m)……………………………….. 52
15 Well log of well 2866 (-760 m to -762.6 m)……………………………… 53
16 Well log of well 2941 (-943.5 m to -947.5 m)……………………………. 54
17 Well log of well 2942 (-984 m to -987.5 m)……………………………… 55
18 Well log of well 2943 (-884 m to -888 m)……………………………….. 56
19 Well log of well 2943 (-888 m to -889.8 m)……………………………… 57
20 Well log of well 2980 (-859.5 m to 863.5 m)……………………………. 58
21 Well log of well 2980 (-863.5 m to -863.8 m)…………………………….. 59 xii
22 Well log of well 2965 (-958 m to -962 m)………………………………… 60
23 Well log of well 2965 (-962 m to -966 m)………………………………… 61
24 Well log of well 2965 (-966 m to -967.2 m)………………………………. 62
25 Photomicrograph showing quartz grains and other features …………….. 64
26 Photomicrograph showing calcite cement …………………………..……. 65
27 Photomicrograph representing a limestone interval ……………………… 67
28 Photomicrograph showing a brachiopod spine …………………………… 68
29 Photomicrograph showing mud drapes ………………………………...... 69
30 Planar-tabular cross-bedded sandstone (Lithofacies Sc)……..…...... 72
31 Trough cross-bedded sandstone with shale partings (Lithofacies Sth)……. 72
32 Massive sandstone with mudstone intraclasts (Lithofacies Smi)………….. 74
33 Massive sandstone (Lithofacies Sm)………………………………………. 74
34 Laminated sandstone (Lithofacies Sl)…..…………………………………. 76
35 Laminated siltstone (Lithofacies SSl)……………………………………. 76
36 Heterolithic sandstone-mudstone with lenticular bedding (Lithofacies SMk)………………………………………………………… 78
37 Heterolithic sandstone-mudstone with flaser bedding (Lithofacies SMf)………………………………………………………… 78
38 Heterolithic sandstone-mudstone with wavy bedding (Lithofacies SMw)……………………………………………………….. 80
39 Heterolithic bedding with ball-and-pillow structure (Lithofacies SMd).. 80
40 Heterolithic sandstone-mudstone with planar lamination (Lithofacies SMl)………………………………………………………… 82
41 Heterolithic laminated siltstone-mudstone (Lithofacies SSMl)…………. 82
42 Heterolithic siltstone-mudstone with bioturbation (Lithofacies SSMb)… 84
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43 Massive mudstone with bioturbation (Lithofacies Mmb)………………. 84
44 Massive mudstone (Lithofacies Mm)…………………………………… 86
45 Massive limestone (Lithofacies Lm)……………………………………... 86
46 Tidal inlet channel assemblage in well 2941…………………………….. 89
47 Tidalite assemblage in well 2980………………………………………… 90
48 Distributary mouth bar sequence in well 2980………………………….. 92
49 Distributary mouth bar sequence………………………………………... 93
50 Point bar sequence in well 2866………………………………………… 95
51 Point bar sequence………………………………………………………. 96
52 Example of Ophiomorpha in well 2866…………………………………. 97
53 Well 2866 core vs. geophysical log comparison………………………… 101
54 Well 2941 core vs. geophysical log comparison………………………… 102
55 Well 2943 core vs. geophysical log comparison………………………… 103
56 Well 2980 core vs. geophysical log comparison………………………… 104
57 Northwest-southeast litho-correlation profile……………………………. 108
58 Northeast-southwest litho-correlation profile……………………………. 109
59 Map of the wells used to create litho-correlation profiles………………. 111
60 Location of wells with their isopach values in meters…………………… 112
61 Isopach map of the “Clinton Sandstone”………………………………… 113
62 3-D subsurface map of the “Clinton Sandstone”………………………… 114
63 Natural fracture from well 2942…………………………………………. 119
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LIST OF TABLES
Table Page
1 Typical fossil assemblage of offshore to shoreface environment………. 12
2 Typical fossil assemblage of an ancient estuarine environment………... 16
3 Stratigraphy column of the “Clinton Sandstone”………………………… 31
4 General composition and stratigraphy of the “Clinton Sandstone”……… 31
5 Fossil assemblage in the “Clinton Sandstone”…………………………… 32
6 Table of cores studied……………………………………………………. 42
7 Missing core information………………………………………………… 42
8 Table of the petrography samples used in this study……………………. 46
9 Wells and additional geophysical used to construct the isopach map….. 47
10 Lithofacies table………………………………………………………… 70
11 Table showing original and new well and API numbers………………. 107
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INTRODUCTION
“Clinton Sandstone”
The Lower Silurian “Clinton Sandstone” is one of the most prolific tight-gas and oil
formations in Ohio (Keltch et al., 1990). However, finding the areas where these hydrocarbons
are located within the “Clinton Sandstone” can be a daunting task. Successful exploration in the
“Clinton Sandstone” requires knowledge of subtle stratigraphic traps based on the depositional
environment and their relationship to production (Keltch et al., 1990).
In the United States, tight-gas formations have been discovered in 23 different basins (Zou et
al., 2013). These tight-gas formations have accounted for 75% of the total unconventional gas
12 3 yield, with estimated recoverable reserves of 5X10 m (Zou et al., 2013).
Most previous workers that have studied the “Clinton Sandstone” believe it is deltaic in nature
(Msek, 1973; Suphasin, 1979; Shadrach, 1989; Bey 2012; and Bloxon, 2012). If correct, the
combination of a deltaic setting, tight sandstones, and possible shale baffles create possibilities
for stratigraphic traps within the “Clinton Sandstone.” Of course, the presence of a stratigraphic
trap does not always ensure a profitable well.
The recent recognition of reservoir compartmentalization has become an important issue
within the oil and gas industry. So much so, that it can affect the booking of reserves an exploration company can claim, which can influence the market value of its stock (Jolley et al.,
2010). Reservoir compartmentalization can be described as separation of petroleum
accumulation into numerous pressure compartments (Jolley et al., 2010). This can occur when
the flow of hydrocarbons is prevented from crossing certain boundaries in a reservoir, thus
significantly reducing the amount of extractable hydrocarbons.
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The ability to find traps and further understand reservoir compartmentalization within a
particular unit can make all the difference in today’s competitive and global hydrocarbon market.
Re-evaluating the “Clinton Sandstones” depositional environment and its 3-D architecture in
Fairfield, Perry, and Vinton Counties, Ohio, could identify new or possibly old areas that may be
worth exploring.
Depositional Environments
Deltas
A delta is formed at the mouth of a river which flows into a larger body of water such as an
ocean, lake, or estuary. Accumulating sediments from the river will generate the delta and its characteristics. Orton & Reading (1993) describes three main factors that control and influence
delta architecture:
1) Sediment supply, which includes sediment load, discharge of water, and drainage basin
features.
2) Accommodation space, which involves tectonics (subsidence, uplift, isostasy, and thermal
processes), eustasy (global sea-level fluctuations), and sediment supply or paleoclimate.
3) Coastal setting, which includes rates of longshore transport or cross-shelf transport, wave
regime, and tidal range.
These processes, acting upon available sediment, can create different depositional features
such as distributary channels, distributary-mouth bars, levees, crevasse splays, interdistributary
bays, beaches, tidal flats, tidal ridges, eolian dunes, and coastal swamps or marshes (Coleman,
1976). A delta complex can be broken down into three regions which include: 1) the upper and
lower delta plain, 2) the delta front (distributary channels and related interdistributary bay
environments), and 3) the prodelta (Figure 1).
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Figure 1. Diagram of a delta complex consisting of upper and lower delta plain, delta front, and prodelta modified (from Posamentier & Walker, 2006).
4
Deltas can be classified as wave-, tide-, or river-dominated deltas. Many modern day examples are actually a mixture of the three, but the degree of each varies. The type of delta greatly influences the shape and features that delta will produce. The Mississippi River is an example of a river-dominated delta, which displays a lobate morphology. A wave-dominated delta will have lobes that are smoothed out in the front and show cusp-like margins, while a tide- dominated delta will form sand bodies parallel to the direction of the tidal currents.
The delta plain commonly contains clay, silt, and sand as well as possible organics and carbonate concretions (Coleman & Gagliano, 1965). Prominent features include distributary channels, point bars, natural levees, crevasse splays, and floodplains. The upper delta plain is typically a tidally-influenced fluvial environment. The lower delta plain is a complex fluvial environment with strong storm wave and tidal influence.
Regions between distributary channels are called interdistributary bays. These features make up the majority of the lower delta plain and can be subdivided into bays, estuaries, crevasse splays, bayhead deltas, salt marshes, and tidal flats. These areas have generally relatively shallow water depths and are dominated by deposition of muds. In the geological record, thin, stacked coarsening-and fining-upward muddy facies successions are common. These deposits are usually not as thick or well-developed as prograding distributary channel sequences (Tye & Coleman,
1989).
The delta front can be defined as the dipping seabed that is adjacent to the shoreline (Elliott,
1986). This area is characterized by distributary mouth bars which deposit a mixture of sand and mud, with grain size decreasing seaward. Waves, currents, and tides are known to dominate the marine processes in this region. River-dominated delta fronts generally consist of a complex
5
arrangement of distributary channels and distributary mouth bars (DMBs) which can amalgamate
to form bar assemblages and depositional lobes (Van Heerden and Roberts, 1988).
Three different kinds of flow can occur in the delta front environment which influences the
way sediment is deposited and the features that may form. Hypopycnal flow is described as
lower density river inflows entering higher density ambient fluids. When this happens, the
inflows form a surface plume that is dispersed by waves, tides, and currents. Hyperpycnal flow is
the opposite of hypopycnal flow and described as higher density inflows entering lower density
ambient fluids. Under these conditions, density underflows are generated, and turbidites can be
deposited. Homopycnal flow occurs when river inflows have the same density as the ambient
fluid. Rapid mixing will occur under these conditions and sudden deposition will take place.
Large features in the delta front include distal bars, distributary-mouth bars, and cresentic or
elongate (“shoestring”) sand bodies. Associated sediments include clay, silt, very-fine to fine-
grained sand, calcareous sand, and organic material. Common sedimentary structures in delta
front settings include lamination, current ripples, oscillation ripples, trough cross-bedding and
festoon cross-bedding. Some of the lamination seen in the delta front can be caused by hydraulic sorting of heavy minerals including zircon, rutile, tourmaline, and limonite (Taylor, 1962).
Coleman and Prior (1982) use the term delta front when only referring to a distal bar environment. Roberts and Sydow (2003) use the term delta front when talking about mid-shelf muddy clinoform strata, which is seaward of any significant sand deposits.
Distributary channels are the main path for fluvial sediment and water into the lacustrine or marine environments. Deposits in these channels are typically sand, but can include clay, silt and occasional pebble lags at the base (Coleman and Gagliano, 1965). Distributary channel deposits usually fine upwards, and contain sedimentary structures such as planar tabular and trough-cross
6
bedding, planar lamination and ripple lamination. Tidal influence can produce tidal bundles, mud
drapes, and reactivation surfaces (Coleman and Gagliano, 1965). Bioturbation and plant rootlet
disturbance (phytoturbation) can be seen in distributary channel sequences, but they are not
common (Coleman and Gagliano, 1965).
Most of the fine-grained deltaic sediment accumulates in the prodelta environment. Prodelta
sediments fine seaward and laterally and eventually transition into shelf muds. Sediment in the prodelta can include rapidly deposited turbidites with characteristic Bouma sequences.
Alternatively, graded rhythmites (silty or sandy beds with normal grading) indicate prodelta deposition by river floods, which reveals that a river mouth must be nearby. Bioturbation indices can be used to estimate the flood frequency in these deposits (MacEachern et al., 2005).
Rhythmically laminated sediments indicate tidal influence (Willis, 2005).
Changes in the position of a delta can produce larger depositional sequences. Progradation can occur when the incoming sediment supply is greater than the amount of sediment being lost due to erosion, subsidence, or an increase in sea-level. Progradation sequences are likely to occur when sediment influx increases rapidly or sea-level falls. A large addition of sediment could be due to tectonism, or eustatic sea-level fall which could be due to a period of climate cooling and the expansion of icecaps. The second sequence is retrogradation, which is when a delta retreats landward. This can happen when incoming sediment is less than what is being lost due to erosion, subsidence, and sea-level fall. Retrogradation could be due to tectonic subsidence or eustatic sea-level rise which could be due to a period of global warming and the melting of the icecaps.
Ichnofacies in a delta can vary based on whether the delta is fluvial, wave, or tide-dominated.
For purposes of this study, the focus will be on tide-dominated ichnofacies. The marine extent
7
can extend into the deltaic plain, therefore, bioturbation can be seen in all delta subenvironments.
The intensity of bioturbation varies from moderate to complete. Trace fossil suites can contain
Planolites, Phycosiphon, Rosellia, Teichichnus, Asterosoma, Diplocraterion, Scolicia, Nereites,
Palaeophycus, Taenidium, and Ophiomorpha (Carmona et al., 2009).
Barrier Islands
Barrier islands are mainly composed of shoreline-parallel sand bodies (Boyd et al., 1992).
These sandy deposits are usually generated by waves and longshore drift, and ultimately act as a buffer between the shoreline and ocean. The size, shape, and structure of barrier islands are directly related to wave energy, sand supply, and the tidal range (Kolditz et al., 2012). Barrier islands partially separate either lagoons or estuaries from marine environments. Barrier islands can form during both prograding and retrograding sequences depending again on changes in tectonics, sea level or sediment supply. Prograding barriers often show a coarsening-upward trend (Figure 2). The seaward side of a barrier island is divided into the foreshore (beachface),
shoreface, and the offshore transition zone, which changes to the offshore region.
Offshore Environment.
An offshore environment is the most distal of the nearshore environments and contains the
finest sediment. Distal environments refer to those that are further offshore while proximal
environments are closer to shore. The offshore environment is located below storm-weather
wave base. Storm-weather wave base is the depth where storm waves first affect the seafloor, and this serves as the boundary between the offshore and offshore transition zone (Peters and
Loss, 2012). Sediments found in modern offshore environments consist of mud, sandy silt, thin sand beds with shell fragments, and plant material. Bioturbation is also very common and trace
8 fossils can consist of Rhizocorallium, Thalassinoides, Phycosiphon, Diplocraterion, Rosselia rotates, Rosselia socialis and Gyrochorte (Seilacher, 1967; MacEarhern and Bann, 2008).
Offshore Transistion Zone.
The offshore transition zone is located between storm-weather wave base and fairweather wave base. Fair-weather wave base is the depth where normal wavebase reaches the seafloor.
The offshore transition zone will be characterized by sandy distal tempestites interbedded with silt and clay, transitioning upward into proximal tempestites, amalgamated tempestites, and swaley stratified sands. Storms can occur in these areas and produce tempestites. These tempestites deposits consist of (in ascending order) erosional sedimentary structures, hummocky stratified sand, planar laminated sand, wave rippled sand, and mud (Figure 3). In the ancient record, deposits from the offshore zone will most likely consist of shale and siltstone interbedded with distal tempestites. Periods of alternating low and high wave energy conditions are common in this setting. Trace fossils commonly found in this area consist of Chondrites, Planolites,
Rosselia rotates, and Schaubcylindrichnus (Seilacher, 1967; MacEarhern and Bann, 2008).
Shoreface Zone.
The shoreface region extends from fairweather wave base to the mean low water at the foreshore (Figure 4). According to Howard and Reineck (1981), the shoreface is the zone of maximum sediment movement. Storms that pass through this area generate shoaling waves and storm currents that erode the shoreface. The eroded sediment is then either transported landward, transported seaward to the shelf region, or transported along shore as longshore drift. The breaker zone is present in the shoreface and splits the shoreface into the lower shoreface
(between FWWB and the breaker zone) and the upper shoreface (between the breaker zone and
9
Figure 2. Stratigraphic section of a prograding barrier island complex showing the transition of coastal zones interpreted from the resulting deposits (modified from Posamentier & Walker, 2006).
10
Figure 3. Typical tempestite sequence (modified from Brenchley, 1989).
11
Figure 4. Diagram of an offshore to a foreshore environment (modified from Posamentier & Walker, 2006).
12
Table 1. Fossil assemblage found in a typical offshore to shoreface environment.
Region Ichno-Taxa References
Rhizocorallium Thalassinoides Phycosiphon Seilacher, 1967 Offshore Diplocraterion Rosselia rotates MacEachern and Bann, 2008 Rosselia socialis Gyrochorte Chondrites Offshore Transition Planolites Seilacher, 1967 Rosselia rotates MacEachern and Bann, 2008 Schaubcylindrichnus Skolithos Arenicolites Diplocraterion habichi Diplocraterion parallelum
Rosselia socialis Seilacher, 1967 Shoreface Asteriacites MacEachern and Bann, 2008 Ophiomorpha Conichnus Psilonichnus Macaronichnus segregatis Skolithos Seilacher, 1967 Foreshore Macaronichnus segregatis MacEachern and Bann, 2008
13
MSL). In the breaker zone, shoaling of waves causes wave height to increase and become
unstable. Features that can be seen in the shoreface include current and wave ripples in the upper
shoreface, cross-bedding in the middle shoreface, and tempestites in the lower shoreface.
Foreshore (Beachface) Zone.
The foreshore experiences the swashing of waves which hit the beach and create a repetitively
wet/dry environment. The swash zone generally creates planar lamination and gravel lag
deposits. The foreshore is also known to have a slightly angled slope which is called the beach
face. A berm can be present and separate the foreshore from the backshore region. Modern beach
sediments consist mainly of sand and gravel. Ancient beach sediments can consist of cross-
bedded, planar laminated, or massive sandstone with interbedded conglomerate.
Lagoons
A lagoon is a body of water parallel to the coast that is separated from the ocean by a barrier island, spit, or reef (Figure 5). Because of this barrier, lagoons have some protection from open ocean waves. Lagoons can form in both humid and arid regions. Humid conditions will result in adjacent wetland environments, while arid conditions will produce adjacent salt flat environments. Subenvironments within a lagoon consist of tidal flats, spillover lobes, wetlands, and tidal inlet channels.
In a clastic shoreline environment, the location of a lagoon is between the backshore (of a barrier or spit) and the mainland. These barriers offer limited protection from storms and tides, but cannot protect a lagoon from river floods (Avramidis et al,. 2013). Sediments will enter a lagoon via river transport, tidal currents from the sea, barrier overwash, or by wind (Avramidis et al., 2013).
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Lagoons commonly trap finer-grained sediments which can be represented in the geologic record as interbedded sandstone, shale, siltstone, coal, or evaporites. Mud is very prevalent, but silt and laminated sand are also common (Bridges, 1976). Peat, shell fragments, and driftwood are also common in modern and ancient lagoon sediments (Madricardo et al, 2007). In the ancient record, lagoon environments that were part of a regressive barrier will form coarsening- upward sequences and contain bioturbation, as well as a wide range of different organisms.
Brackish-water assemblages of ichnofacies can consist of Skolithos, Teichichnus, Arenicolites,
Gyrolithes, and Planolites (Pemberton et al., 1982).
Estuaries
An estuary is a tidally influenced river mouth that receives freshwater runoff. As estuaries develop, sediment being transported along the shore will commonly form spits or barriers in front of the mouth of the estuary. In most cases, these barriers only moderately close off the estuary to the open ocean. Wave-dominated and tide-dominated are the two main types of estuaries. They are transgressive in nature and have received a lot more attention from sedimentologists in the past couple decades because they may contain hydrocarbons (Zaitlin et al., 1995).
Wave action greatly influences the facies present in a wave-dominated estuary. The mouth of the estuary will develop coarse-grained transgressive bars and form inlets along the beach and shoreface barriers (Schroder-Adams, 2006). The fluvial system will deliver sand and gravel to the bay-head delta, while the central basin of the estuary accumulates organic-rich muds
(Schroder-Adams, 2006). Wave-dominated estuaries tend to be dominated by mud in the central region, while the areas closer to land are sandier. Tide-dominated estuaries are less common than
15
Figure 5. Generalized lagoonal sequence (adapted from Horne and Ferm, 1978).
16
Table 2. Trace fossil assemblages typical of estuarine environment (modified from Ranger and Pemberton, 1992).
Taxa
Cylindrichnus
Ophiomorpha
Teichichnus
Planolites
Rhizocorallium
Thalassionoides
Diplocraterion
17 wave-dominated estuaries. Tides will reach further into the estuary and the finer-grained sediments will accumulate in marshes and tidal flats
that develop along the edges of the estuary. Coarse-grained sand will be deposited as bars in the central part of the estuary (Dalrymple et al., 1992). Tidal rhythmites can be common in the geological record when looking at a tidally influenced estuary. Cross-bedded and ripple laminated sands are very common in a tide-dominated estuary (Ludwick, 1975).
Estuaries are created from a transgressive event. Typically, an estuary forms when an alluvial incised valley is flooded by sea level rise. This flooding event will deposit estuarine sand and mud above previous fluvial deposits, or these previous fluvial deposits may be reworked and possibly eroded by tidal and wave influence. Estuaries typically display an overall fining-upward sequence (Miall, 1977). The mouth of an estuary can be identified by the presence of shell deposits and wave-tidal structures. The inner area of an estuary will be much muddier and may contain clay, roots, peat, and sand lenses in massive mud closer to the mouth (Allen, 1991). The area closer to the alluvial plain will contain more sand and display cross-bedded sand with clay laminae, flasers, and mud drapes (Allen, 1991).
Tidal Flats
Tidal flat environments are located along the margin of the shoreline in areas of significant tidal range. Typically they have low-relief. Tidal flats typically extend from the subtidal zone to the intertidal zone to the supratidal zone (Figure 6). The term “tidal flat” can be further broken down into sand flat, mixed flat, and mud flat environments. Some features indicative of a tidal flat include mud drapes and tidal rhythmites. Mud drapes will be deposited during a period of slack water conditions, while tidal rhythmites are the product of diurnal and neap-spring variations in tidal-current speed (Dalrymple et al., 1991). Other types of bedding that can be
18
Figure 6. Diagram of a tidal flat environment broken down into sand flat, mixed flat, and mud flat (modified from James and Dalrymple, 2010).
19
present, but are not limited to a tidal flat include flaser, wavy, and lenticular bedding. Flaser
bedding will consist of mainly sand but contain some small mud lenses, lenticular bedding is the
opposite and is mainly mud with few sand lenses, and wavy bedding is closer to an equal mixture
of sand and mud.
The subtidal zone is the area furthest from land and is submerged most of the time. Only
during extreme low tides will this area be exposed. Tidal channels and sand flats are common in
the subtidal zone and may contain biogenic material. Features like cross-bedded and flaser
bedded structures are common in this zone.
The intertidal zone is located above the subtidal zone and can contain sandflats, mixed flats,
and mud flats. This area is exposed more often than the subtidal zone and the energy created in
this environment is less than that of the subtidal zone. Because of that, less sand and
more mud are present. Features such as flaser, wavy, and lenticular bedding are common in the
intertidal zone.
The supratidal zone is located above the intertidal zone and is rarely submerged with water.
Salt marsh deposits can be present in the supratidal zone, as well as paleosols, coal, evaporites, mudcracks, brecciation, and possibly storm deposits. Bioturbation is not as common in the supratidal zone as it is in the intertidal and subtidal zones.
Tidal flats are typically muddy environments, but are also known to hold extensive amounts of sand. The availability and composition of nearby sediment will determine the scale of flat which will evolve (Fan et al., 2004). The sand flat is the area that is subject to maximum tidal wave energy, and thus contains the coarsest sediment. The deposits will include crossbedded, ripple laminated, and flaser bedded sand with mud drapes. The mixed flat is the lower part of the intertidal zone, transitional between sand flats and mud flats. The deposits include heterolithic
20
Figure 7. Diagram showing flaser, wavy, and lenticular bedding (modified from Reineck and Wunderlich, 1968).
21
flaser bedded, wavy bedded, lenticular bedded sand and mud, with extensive bioturbation
(Figure 7). The mud flat is the upper part of the intertidal zone. It consists of heterolithic
lenticular bedded sand and mud and planar bedded sand, silt and mud with extensive
bioturbation. Mudcracks may be present.
Purpose and Goals
The Lower Silurian “Clinton Sandstone” in eastern Ohio is a well-known productive tight-gas
unit that produces both oil and gas. Starting back in the late 1800s, the “Clinton Sandstone” has
received a lot of attention for its hydrocarbon potential. The interest for exploring and
drilling into the “Clinton Sandstone” still remains high. But to efficiently extract hydrocarbons
from this unit, the depositional environment and 3-D structure must be better understood since it
is an unconventional tight-gas reservoir. For conventional wells, the point of studying the
subsurface is to find whether or not traps have evolved into hydrocarbon reservoirs at the right
time (Zou et al., 2013). But for unconventional wells, one must decide if oil and gas are
continuous in distribution, while also evaluating physical properties, lithology, brittleness, and
oiliness (Zou et al., 2013). Oiliness can be defined as the amount of oil a sample or interval
contains.
According to Msek (1973) and Bakush (1975), the “Clinton Sandstone” is deltaic and is
organized into elongate sand bodies which could serve as reservoirs if these sand bodies were
connected to source rocks during oil migration, and if there are seals to trap the hydrocarbons.
Because such tight-gas or tight-oil units could retain significant oil even after most of the
formation was drilled, secondary production techniques (such as chemical injection, gas injection, or thermal recovery) may need to be used. The hypothesis for this study is that the
“Clinton Sandstone” was a tidally-influenced delta with significant stratigraphic traps. It is also
22
assumed that horizontal drilling as well as hydraulic fracturing will be more beneficial and
successful for hydrocarbon production than conventional vertical drilling techniques. Testing this hypothesis will include construction and evaluation of an isopach map and 3-D subsurface map of the study area, as well as core descriptions and thin section analysis.
Initial reasons for these hypotheses are the obvious and frequent presence of mudstone within the core samples. The strong presence of mud indicates that tidal influences were profound in this study area. There are also two distinct mudstone layers, according to previous workers
Bakush (1975) and Msek (1973), that separate the three sandstone bodies (Stray, Red, and
White) from one another in the subsurface. The Brassfield Limestone, which is situated overtop the “Clinton Sandstone,” acts as a caprock and has the capability of holding hydrocarbons in the
“Clinton Sandstone.”
The goals for this project are to 1) identify the depositional environment of the “Clinton
Sandstone” in the study area, 2) develop a 3-D model for the subsurface and 3) assess the
petroleum implications of the area by describing well samples, correlating geophysical logs, and
observing thin sections. Gaining a better understanding of the depositional environment may
reveal the types of features that have potential for successful oil or gas exploration. A 3-D model
may illustrate properties of the “Clinton Sandstone” in the subsurface to control future horizontal drilling. The physical data consisting of well samples, geophysical logs, and thin sections will give a large, intermediate, and small scale look at the “Clinton Sandstone” in this particular study area and help to identify subsurface trends, environments present, and small scale features that may be beneficial or detrimental to hydrocarbon exploration.
23
GEOLOGICAL BACKGROUND
Geological Setting
The Silurian (443-416 Ma) was a unique time interval for Ohio geology (Figure 7). According to Hansen (1998), Ohio was located south of the paleo-equator during high global sea level
(Figure 8). There was significant reef formation and the barriers created from these reefs restricted the oceanic circulation, favoring evaporite precipitation (Figure 9). These conditions were also favorable for hydrocarbon accumulation because black shales served as source rocks, the carbonates were excellent reservoir rocks, and salt tectonics helped create traps.
The Taconic Orogeny took place in eastern North America around the end of the Ordovician
(Rodgers, 1971) (Figure 10). This orogeny consisted of mountain building and island arc accretion. As a result of the Taconic orogeny, flexural-loading and subsidence of the Laurentian carbonate shelf created the Appalachian basin (Quinlan and Beaumont, 1984). The basin floor continued to subside throughout the rest of the Paleozoic, due to flexural-loading in the Late
Devonian Acadian orogeny and Late Paleozoic Allegheian orogeny (Faill, 1997). Thus, these
Silurian events mark an early phase of the creation of the Appalachian basin.
In Ohio, the Appalachian basin is delineated by the Cincinnati arch and Findlay arch on the west, and the Taconic highlands on the east (Faill, 1997). In present time, the Cretaceous overlap of the Mississippi embayment in Alabama represents the Appalachian basin’s southwestern limit
(Faill, 1997).
The study area is located in the west-central portion of the Appalachian Basin. In the subsurface, the “Clinton Sandstone” increases in depth from the northwest on the basin margin,
24
Figure 8. Geological map of Ohio. Black box outlines the study area of this thesis (adapted from Slucher et al, 2006).
25
Figure 9. Representation of the United States during the early Silurian period. The study area is located within the black box. A global view of the early Silurian is in the bottom-right of the picture (modified from Blakey, 2011).
26
Figure 10. Distribution and relationship of reefs and platforms that developed during the Silurian. Study area is located within the black box (modified from Hansen, 1998).
27
to the southeast, toward the basin axis (Boley et al., 1965). For example, in northwest Knox
County and southeast Noble County, Ohio, the base of the “Stray Clinton” interval changes from
-335 meters (below sea level) in the northwest part of Knox County to -1426 meters in southeast
Noble County (Bakush, 1975). Using a three-point method calculation, the “Clinton Sandstone” dips about 11m per km to the southeast and strikes N11○E (Msek, 1973). Folds are present in a
few areas that create small closures in this subsurface geometry; however major structural
closures have not been observed (Msek, 1973).
Regional Stratigraphy
Cabot Head Shale
The Cabot Head Shale underlies the “Clinton Sandstone.” The unit is mainly composed of
interbedded shale, quartz siltstone, and fine-grained quartz sandstone (Knight, 1969). Most of the
Cabot Head Shale is planar laminated, lenticular bedded or wavy bedded, greenish-black to dark
heterolithic siltstone and shale (Knight, 1969). Horizontal bioturbation is common in both the
shale and siltstone beds. The unit also exhibits shale folds, load cast structures, and convoluted
bedding (McMullin, 1976).
Shadrach (1989) closely studied the Lower Silurian Albion Group in Medina County, Ohio,
and suggested that the lower portion of the Cabot Head Shale represents a muddy shelf sequence,
while the middle part of the Cabot Head Shale represents a prodelta environment, and the upper
portion of the Cabot Head Shale transitions into the delta front environment of the “Clinton
Sandstone.” Evidence for this is illustrated in the 110 ft slice map, which shows that the silty
prodelta front was deposited over the southeastern one-third of Medina County (Shadrach, 1989).
28
Figure 11. Map of the Appalachian basin (modified from Faill, 1997). Box represents study area. AD = Adirondacks; N =New York; V = Virginia
29
The slice map at 110 ft represents the depth interval of interest from the top of the “Clinton
Sandstone” in a particular area.
Neahga Shale
The Neahga Shale immediately overlies the Stray Clinton interval of the “Clinton Sandstone” and is laterally equivalent to the lower Brassfield Limestone (Osten, 1982). However, this unit has been referred to as the Upper Cabot Head Shale (Knight 1969; McMullin, 1976; and Osten,
1982). According to Urian (1986) and Wieckowski (1986), who studied the “Clinton Sandstone” in east-central Ohio, the iron-rich Neahga Shale is not part of the Cabot Head Shale. Shadrach
(1989) agreed with Urian (1986) and Wieckowski (1986) and urged that the use of “Upper” and
“Lower” Cabot Head Shale be discontinued. For this study, the Neahga Shale will be the name used to identify the shale overlying the “Clinton Sandstone” and the Lower Cabot Head shale below the “Clinton Sandstone” will be referred to as the undifferentiated Cabot Head Shale.
According to Hettinger (2001), the Neahga Shale is part of the Clinton Group, which immediately overlies the Lower Silurian “Clinton Sandstone.”
The Neahga Shale has been described as a hematitic shale with interbedded dark green glauconite shales and gray-green chloritic shales (Smiraldo, 1985; and Urian, 1986). Beds within the Neahga Shale are typically discontinuous and irregular. Bioturbation is widespread
(Wieckowski, 1986). The presence of interbedded glauconite and hematite in the Neahga Shale was evaluated by Wieckowski (1986) and she offered three explanations as to how there could be hematite in shallow marine shales: 1) hematite is authigenic, resulting from intrastratal alteration of iron bearing detrital grains, 2) iron was released by weathering igneous or metamorphic source rocks, and 3) a high energy environment scoured hematite coatings from the underlying “Stray Clinton” and transported the iron seaward.
30
Packer Shell or Brassfield Limestone
The Packer Shell or Brassfield Limestone is the uppermost member of the Lower Silurian
Albion Group. The term “Packer Shell” is an informal name that has been used by drillers for many years. The proper name for this unit is the Brassfield Limestone, which is present in Ohio, western New York, and Ontario.
The Brassfield Limestone is a gray to dark gray, dense crystalline, bioclastic limestone
(Urian, 1986), and a fine to medium crystalline, dolomite interbedded silty shale, silty sandstone, and bioclastic limestone (McMullin, 1976). The unit is typically undulose bedded or planar bedded limestone. Fossils observed in this unit consist of echinoderms and mollusca (Nelson and
Coogan, 1984).
“Clinton Sandstone”
Stratigraphy and Age
The “Clinton Sandstone” was first described in 1887 by drillers in Fairfield County, Ohio.
This subsurface unit extends from near the Cincinnati Arch on the west to portions of West
Virginia on the east (Bonine, 1915). It is early Silurian in age based on its correlations to the
Thorold Sandstone and the Grimsby Sandstone (McCormac et al., 1994). The unit has been subdivided into three informal sandstone units (Table 3). They are, in ascending order, the
“Second or White Clinton”, the “First or Red Clinton”, and the “Stray Clinton” (Bonine, 1915).
Each of these three sandstone bodies are separated by thin shale intervals (Table 4). There are no known surface exposures of the “Clinton Sandstone” in Ohio (Msek, 1973); so researchers must rely on drill cuttings, core samples, and geophysical logs to evaluate and understand this unit.
31
Table 3. Stratigraphic column of the Lower Silurian Albion Group (modified from Shadrach, 1989).
Table 4. General composition and stratigraphy of the “Clinton Sandstone” (modified from Msek, 1973).
Interval Composition Grain size Roundness Cementation Sandstone, some Fine to very fine- Sub angular to More silica than Stray Clinton siltstone grained sub rounded calcite Sandstone, some Very fine- Sub angular to More silica than First Clinton siltstone grained sub rounded calcite Second Sandstone, some Fine to very fine- Sub angular to Calcite and Clinton siltstone grained sub rounded secondary silica
32
Table 5. Fossil assemblage in the “Clinton Sandstone.”
Major Groups References
Echinoderms Msek, 1973
Bryozoans Msek, 1973
Msek, 1973 Brachipods Wieckowski, 1986
Conodonts Kleffner, 1985
33
The units below the “Clinton Sandstone,” from oldest to youngest, consist of the Whirlpool
Formation, the Manitoulin Dolomite, and the Cabot Head Shale. Units above the “Clinton
Sandstone,” from oldest to youngest, consist of the Neagha Shale and the Packer Shell (Table 3).
Drillers believed that the “Clinton Sandstone” interval in Ohio correlated with the well-known
Clinton Group of New York State, which is Middle Silurian in age. They perceived this based on the appearance of the “Clinton Sandstone.” However, later researchers were able to prove that the Lower Silurian “Clinton Sandstone,” or Clinton Formation according to Bloxson (2012) and the Ohio Division of Geological Survey (2004), is not related to the Middle Silurian Clinton
Group. Patchen (1968) correlated the “Clinton Sandstone” with some upper parts of the
Tuscarora Sandstone in West Virginia and Pennsylvania.
The “Clinton Sandstone” is now believed to be part of the Albion Group, which correlates with the Castanea Sandstone, Tuscarora Sandstone in Pennsylvania, and the Clinch Sandstone in
West Virginia (Yeakel 1962; Smosna and Patchen, 1978), or with the Cataract or Medina Group in New York and Ontario (Swartz et al., 1942; Martini, 1971). Furthermore, the three distinct sandstone bodies within the “Clinton Sandstone” (Stray, Red, and White) can also be assigned proper nomenclature: the “Stray Clinton” is equivalent to the Thorold Sandstone, the “Red
Clinton” corresponds to the Cabot Head Sandstone, and the “White Clinton” parallels the
Grimsby Sandstone (Ohio Division of Geological Survey, 1985). This study will use the informal stratigraphic nomenclature of “Clinton Sandstone” accepted by the oil and gas industry in Ohio.
Lithology
In general, the “Clinton Sandstone” in southeast Ohio is a very fine to fine-grained, subrounded to subangular, light gray to brown sandstone with minor siltstone and mudstone
34
(Msek, 1973). A petrographic study of the “Clinton Sandstone” in Perry, Morgan, and Hocking
Counties, Ohio and found that sandstone composition ranges from quartz arenite to
sublitharenite. Almost 95% of the unit consists of clear to white, quartz sand grains that are cemented by calcite, silica, or hematite (Msek, 1973). The sandstone bodies in the “Clinton
Sandstone” are often separated and interrupted by shale partings (mud drapes).
The Stray Clinton, as described by Msek (1973), ranges in grain size from 0.02 mm to 0.3 mm. Sorting of this unit is generally very good, and grain size tends to increase upward.
The grain size in the First Clinton varies from 0.03 mm to 0.27 mm (Msek, 1973). This unit was a bit coarser grained than the other two units, but still deemed to be well sorted in most areas.
The “Second Clinton” was very similar to the Stray Clinton and ranged in grain size from
0.02 mm to 0.3 mm (Msek, 1973). This unit showed a fining-upward sequence and varies from moderately well to well sorted (Msek, 1973).
Depositional Environment
Some of the earliest reports on the oil and gas fields in Ohio included information about both the Berea Sandstone and “Clinton Sandstone” intervals (Bownocker, 1903; 1911). The tight nature of the “Clinton Sandstone” was not well understood at this time, but oil production was believed to be dependent on variable thickness and pinch outs of sandstone. O’Rourke (1941) made an effort to address the problems of development and exploration of the “Clinton
Sandstone.” This was later expanded on by Alkire (1952) who researched the producing sands in
Perry County, Ohio, which included the “Clinton Sandstone.” Alkire (1952) stated that the
“Clinton Sandstone” was deposited by an advancing sea which was carrying sediment from the
35 mountains to the east and northeast. These sediments formed sand bars near the shoreline and are the zones of porosity where oil and gas has accumulated (Alkire, 1952).
Mikan (1973) performed a paleoenvironmental interpretation of the “Clinton Sandstone” located in Guernsey County, Ohio. The lower Grimsby Sandstone or “Second Clinton” was interpreted as part of a delta-front environment. The upper Grimsby Sandstone or the “First
Clinton” was interpreted as a delta plain environment while, the Thorold Sandstone or “Stray
Clinton” was interpreted as a distal to proximal delta-front environment. Mikan (1973) also indicated that the shales separating the “Second, First, and Stray Clinton” intervals were remnants of prodelta deposits laid down during slight transgressions.
Msek (1973) conducted a petrographic study of the “Clinton Sandstone” in the areas of Perry,
Morgan, and Hocking counties, Ohio, with the goals of describing the depositional environment, as well as enhancing oil and gas production. His study concluded that the “Clinton Sandstone” formed a series of elongate thin sand bodies that resembled delta distributary channels and distributary channel bars. Reasoning for this includes information from isopach maps which show the thicker belts of the “Stray Clinton” overlying the thinner belts of the “Red Clinton,” which in turn overlie the thicker belts of the “White Clinton” (Msek, 1973). The changes in trends and thickness are likely due to shifts in the course of distributary channels during the time of deposition (Msek, 1973).
Bakush (1975) studied the area immediately north of area researched by Msek (1973), and the main focus of his study was to identify the structural and stratigraphic characteristics of the
“Clinton Sandstone.” Bakush (1975) concluded that the “Clinton Sandstone” represented channel sand bars in the eastern portion of his study while the western portion was indicative of barrier island and lagoon facies. His reasoning was that the “Second Clinton” gradually decreased in
36
shale content upward and that this particular sand body was more like an offshore bar. In
contrast, the “First Clinton” appeared to be much more variable laterally; this suggested that it represented parts of a subaerial delta (Bakush, 1975).
Suphasin (1979) studied the environment of the “Clinton Sandstone” in the subsurface of
Trumbull County to interpret the depositional environment. In this area, the “Clinton Sandstone” demonstrates many facies changes, so Suphasin (1979) decided it was not possible to produce
subsurface facies maps. The “Clinton Sandstone” in the subsurface of Trumbull County was
interpreted as upper and lower deltaic plain environments based on the alternating sequences of
distributary channels and bars. The main reasoning behind this hypothesis is the presence of
thick and well-developed sandstones, which symbolize the main progradation of the deltaic
system (Suphasin, 1979).
Keltch (1985) studied the depositional systems and reservoir quality of the “Clinton
Sandstone” in Guernsey County, Ohio. His main goals were to identify the depositional systems
of the reservoir sandstones, explore the differences in size, shape, and distribution of these
reservoirs, describe the reservoir’s production history, and identify the best exploration strategy.
The “Clinton Sandstone” interval was interpreted as having five main depositional environments which consisted of meander point bars, proximal crevasse splays, distributary mouth bars, distributary channels, and transgressive sands (Keltch, 1985). These environments were determined based on log signatures and two cores from the “Clinton Sandstone.” Keltch (1985) states that distributary mouth bars can be identified by a coarsening upward sequence that consists of sand and silt, while also displaying an abrupt termination. Meander point bars and proximal crevasse splays will show a fining-upward log signature while distributary channels
37 will display a blocky log profile (Keltch, 1985). The transgressive sands will appear on a geophysical logs as short and intermittent pulses of sand (Keltch, 1985).
Shadrach (1989) studied the “Clinton Sandstone” in Medina County to identify the depositional environment and any structural patterns that may be present. He describes “Clinton
Sandstone” as being both upper and lower delta plain based on conclusions from previous authors. Shadrach (1989) finds the “Stray Clinton” to be a strand plain deposit based on constructing a 20-foot slice map that shows a continued transgression and reworking of the
Clinton sands. Slice maps show the percentage of composition of several rock units at a particular depth, so this particular slice map was at a depth of 20 ft from the top of the “Clinton
Sandstone” in that area. A diagrammatic structural cross section of Portage, Medina, and Summit counties was constructed by Shadrach (1989), which shows three different sloping surfaces.
These sloping surfaces most likely represent ancestral hinge zones which may have controlled basin subsidence. Shardrach (1989) states that these areas of subsidence controlled the form and advance of the deltaic plain facies and that the three different sloping areas break coincidently with the upper and lower delta plain limits.
Petroleum Geology
The study area incorporates three counties located in close proximity to one another, but having profoundly different oil and gas production records. Maps and charts that display the number of wells drilled per county, show that the majority of successful wells are located in central and eastern Ohio. Fairfield, Perry, and Vinton Counties are located in this region of high productivity. They are not as prolific as more eastern counties in Ohio, but they all were solid producers of oil and gas for a several decades (Figure 11).
38
In Fairfield County, there are currently about 124 wells producing from a total of 3,102 wells on file (Drilling Edge, 2014A). Production from Fairfield County has been 55,982 barrels of oil and 315,934 MCF of gas as of 2012 (Drilling Edge, 2014A). In similar fashion to Perry County,
Fairfield County’s production numbers have been decreasing since 2001.
Of the three counties, Perry County is the most productive having about 1,064 producing wells from as many as 12,144 wells drilled since the late 1800s (Drilling Edge, 2014B).
Production from Perry County has been 114,607 barrels of oil and 421,666 MCF of natural gas as of 2012 (Drilling Edge, 2014B). However, the oil and gas production trend in this county has been declining since 1996.
Vinton County is least productive of the three counties. It has about 85 productive wells of
2,070 drilled (Drilling Edge, 2014C). Production from Vinton County has been 16,087 barrels of oil and 55,597 MCF of gas as of 2012 (Drilling Edge, 2014C). Despite the smaller numbers,
Vinton County has actually seen a small increase in the production of oil, which has climbed from 10,227 barrels per year in 2010 to 16,087 barrels per year in 2012 (Drilling Edge, 2014C).
Gas production has also slightly increased from 49,483 MCF in 2009 to 55,597 MCF in 2012
(Drilling Edge, 2014C).
The reservoir characteristics of the “Clinton Sandstone” are generally less than adequate for a conventional oil reservoir. Miller (1982) found that porosity of the “Clinton Sandstone” in Stark
County ranged from 0 – 13%, and Msek (1973) found porosity ranged from 8 – 14% in Perry
County, Ohio. Permeability within the “Clinton Sandstone” is usually within the 2-6 mD
(millidarcy) range (Knight, 1969). The reasons for this low porosity and permeability could be related to silica and calcite cement, changes in grain size, sorting, and interstitial clay in the sandstones (Suphasin, 1979).
39
Figure 12. Map of Ohio showing all ‘Clinton Sandstone” wells drilled from 1897 through 2004 (modified from Ohio Division of Geological Survey, 2004.)
40
METHODS
Field Methods
Diamond Drill Cores
The initial step taken was to investigate diamond drilled cores from Perry, Fairfield, and
Vinton Counties (Figure 12). These cores were located within the H.R. Collins Laboratory,
which resides in Delaware County, Ohio. The six cores studied have provided information on
lithology, small-scale sedimentary structures, lithofacies and microfacies, as well as depositional
sequences. Msek (1973) and Bakush (1975) both used diamond drill core samples of the Clinton
Sandstone for their research. These authors found various features including flaser bedding and
clay lenses, which will help with identifying patterns in depositional sequences in addition to
determining the overall depositional environment.
All six of the cores examined were from the “Clinton Sandstone” and totaled a length of 32.5
meters (Table 6). These cores were drilled back in the 1960s and 1970s and had been handled
many time before because the cores were slabbed and typically broken every 5 – 10 cm. The
depth of these wells ranged from -758 m to -986.5 m. The geophysical logs that correspond to
the wells researched for this study as well as eight additional geophysical logs used for the 3-D
architecture can be found in Appendix A: Geophysical Logs. At the time of examination, the
cores were in fair condition. It was apparent that these cores had been handled in the past
because all six of the cores were slabbed and broken every few centimeters. Trying to locate
missing sections was nearly impossible and the amount of core missing in each well was
estimated to range from 0.77 m to 1.87 m (Table 7).
41
Figure 13. Map of the study area and wells.
42
Table 6. Table of cores studied and other relevant information.
County Core Township Core Interval Owner Date Number Completed Fairfield 2866 Rush Creek 2487-2505 ft Cosper Well 10/13/1978 Perry 2943 Reading 2900-2921 ft Kentucky Drilling 03/19/1973 Perry 2942 Pike 3220-3237 ft Jeanie Enterprises, LLC 03/06/1973 Perry 2941 Jackson 3096-3120 ft Jeanie Enterprises, LLC 10/16/1972 Vinton 2980 Swan 2820-2839 ft Kentucky Drilling 08/18/1973 Vinton 2965 Wilkesville 3143-3177 ft Karl Wehmeyer & Company 12/29/1961
Table 7. Length and missing sections from core studied.
County Core Number Core Interval Core Missing Total Length of Core Observed Fairfield 2866 2487-2505 ft 2.55 ft 15.45 ft Perry 2943 2900-2921 ft 2.66 ft 18.34 ft Perry 2942 3220-3237 ft 5.58 ft 11.42 ft Perry 2941 3096-3120 ft 6.15 ft 17.85 ft Vinton 2980 2820-2839 ft 3.35 ft 15.65 ft Vinton 2965 3143-3177 ft 3.42 ft 30.58 ft
43
A full description of each core was performed using a hand lens, a tape measure, and 1 m logging sheets with ten centimeter subdivisions (Appendix B: Core Logs). The descriptions include grain size, mineralogy, and sedimentary structures based on centimeter scale. The full length of each core was photographed in sections no larger than 30 cm. Each photograph was also labeled based on the well number, depth, and orientation.
Geophysical Log Analysis
Geophysical logs have been acquired for five of the six wells where the cores were obtained, as well as 11 additional logs in the surrounding areas. These geophysical logs provide gamma- ray, density, and neutron porosity readings. The gamma-ray log is a measurement of emitted radioactivity from the subsurface. It is mainly used to identify shales in the subsurface, but can also better describe the composition of a sandstone by identifying higher amounts of clay minerals or feldspars. Bakush (1975) used the gamma-ray log to identify the boundaries between the “Stray Clinton, Red Clinton, and White Clinton”, because each section is separated by a thin shale interval. The density log was used to help differentiate between sandstones and dolostones since dolostones have greater densities than sandstones. The neutron porosity log is important because it measures the amount of hydrogen present in the strata units. This information can identify bodies with water, gas, or oil. It was also used to help classify the subsurface, because shales receive a high reading while limestones, sandstones and dolostones will generate lower readings.
Eleven additional geophysical logs in surrounding areas of the six cores were obtained for purposes of generating 3-D architecture . This 3-D architecture of the subsurface was produced with the use of geophysical logs, assistance of stratigraphic correlations, and facies analysis. The
44 architecture that is produced will show the overall trend of the “Clinton Sandstone,” which could help identify the depositional environment, as well as assist in oil and gas exploration.
Laboratory Methods
Thin Section Analysis
Sampling from the core depended on the lithofacies and uncertainty of what the lithofacies represented. A total of 28 samples were taken from the six cores studied, but only 16 were made into thin sections (Table 8). The 16 thin sections from core samples were made from billets.
These billets were then sent to Applied Petrographic Services, Inc., located in Greensburg,
Pennsylvania, to be made into thin sections. These thin sections were used to examine the microfacies present. Microfacies analysis was useful when trying to identify small scale depositional environments or sub-environments. The microfacies analysis augmented the larger scale lithofacies analysis when examining the diamond drill cores. Msek (1973) used thin sections in his petrographic analysis of the “Clinton Sandstone” and was able to determine composition, grain size, packing and orientation, which ultimately assisted him in roughly identifying the depositional environment in Hocking, Morgan, and Perry Counties, Ohio.
Analytical Methods
Isopach maps
Isopach maps are used to demonstrate the thickness of sandstone bodies in the subsurface. In regards to this project, an isopach map is used to show the thickness of the “Clinton Sandstone” in the subsurface. The information that was used to produce this map came from diamond drill cores and geophysical logs from the Ohio Department of Natural Resources (Table 9). The isopach map was generated with the help of the computer program Surfer (Golden Software,
2011). The outcome is a contour map showing lines of equal sandstone thickness. The isopach
45
map was used in identifying trends in the subsurface and also assisted in the 3-D architecture portion of this study.
46
Table 8. Table of the petrography samples used in this study.
Sample# Core# Depth (ft) Description 1 2866 2487’ Tan sandstone with cross-bedding 2 2866 2493’ Tan sandstone with mud chips and shale partings (mud drapes) 3 2866 2501’ Maroon sandstone with shale partings 4 2941 3097’ Light gray sandstone with shale flasers 5 2941 3098.5’ Maroon and gray sandstone with mud chips and shale partings 7 2942 3220’ Light gray sandstone with a shale parting and mud chips 10 2942 3237’ Limestone 11 2943 2900’ Tan sandstone with mudstone intraclasts 12 2943 2903’ Heterolithic bedding (laminated) 14 2943 2916’ Limestone 16 2980 2829’ Laminated sandstone and silt with mudstone and deformation structure 18 2965 3164’ Gray siltstone 20 2965 3171’ Tan laminated sandstone 26 2965 3143’ Siltstone with shale partings and flasers 27 2980 2829’ Heterolithic siltstone-mudstone 28 2866 2494’ Tan sandstone with shale partings and mud chips
47
Table 9. Wells and additional geophysical logs used to construct the isopach map.
Depth of Total Depth Well or API # County Township Interval (feet) (feet) API # Fairfield Pleasant 2324 - 2349 25 34045204650000 API # Hocking Falls 2701 - 2736 35 34073226160000 API # Perry Hopewell 2706 - 2725 19 34127267800000 API # Perry Monday Creek 2932 - 2971 39 34127268100000 Well 2866 Fairfield Rush Creek 2487 - 2505 18
Well 2941 Perry Jackson 3096 - 3120 24
Well 2943 Perry Reading 2900 - 2921 21
Well 2980 Vinton Swan 2820 - 2839 19
API # Vinton Madison 3005 - 3026 21 34163205850000 API # Vinton Brown 3452 - 3476 24 34163208730000 API # Vinton Elk 2750 - 2773 23 34163202540000 API # Fairfield Walnut 2355 - 2380 25 34045205000000 API # Fairfield Liberty 1899 - 1903 4 34045209720000 API # Hocking Marion 2544 - 2559 15 34073206350000 API # Hocking Washington 2955 - 2981 26 34073206120000
48
RESULTS
Well Stratigraphy
Well 2866
In well 2866 (drilled in Fairfield County), the majority and lower part of the well shows thick sandstone bodies that are indistinctly cross-bedded (Appendix B: Core Logs). These sandstones also contain mud chips, mud drapes, and occasional mudstone intraclasts. The lower portion of the well fines-upwards. Color of the sandstone in this well changes from red to a light grey when moving toward the middle section. The change in color signifies the shift from the “Red Clinton” to the “Stray Clinton.” Transitioning into the middle portion of the well, there are a few occurrences of bioturbation, mud drapes, flaser bedding, and lenticular bedding, but most of this interval is wavy bedded. A coarsening-upward sequence is present in the middle section of the well. The top portion of the well consists of heterolithic sandstone-mudstone bedding, and also fines-upwards. The overall thickness of this well is 4.71 m. Depth of this well begins at -2487’ and ends at -2505’.
Well 2941
In well 2491 (drilled in Perry County), the bottom 54 cm of the well is muddy and contains shale bodies that range from 6 – 20 cm thick with sandstone in between (Appendix B: Core
Logs). This sandstone does contain some mud chips, mudstone intraclasts, and small mud drapes. The well coarsens-upwards from the bottom to the middle portion, where massive sandstone bodies are present. The sandstone in this well is white on the bottom, and then changes to red when transitioning toward the top, which signifies the change from the “White Clinton” to the “Red Clinton.” Most of the middle and top portion contain thick sandstone bodies with indistinct cross-bedding. The majority of these sandstones are clean (no mud present), but there
49 are few occurrences of mud chips, mud drapes, and mudstone intraclasts. The well fines-upwards from the middle to the upper section. Moving to the upper portion of the well, sandstone with some mud drapes and some bioturbation can be seen. The very top of the well is heterolithic sandstone-mudstone bedding, which shows a coarsening-upward sequence. The overall thickness of this well is 5.44 m. Depth of this well begins at -3096’ and ends at -3120’.
Well 2942
In well 2492 (drilled in Perry County), the very bottom contains a 3 cm interval of limestone
(Appendix B: Core Logs). This limestone is rare and most likely the product of a storm deposit from a nearby offshore environment. The next 17 cm of this well becomes increasingly muddy and contains convoluted bedding. This quickly transitions into multistory sandstones that are interrupted by frequent mud drapes. The very top portion contains both sandstone and mudstone with mud drapes and bioturbation. These sandstones are typically about 2 - 6 cm thick, have occasional bioturbation, and contain some mud chips and mudstone intraclasts. The sandstones in this well are all lightly colored. The overall thickness of the well is 3.48 m. Depth of this well begins at -3220’ and ends at -3232’
Well 2943
In well 2943 (drilled in Perry County), the bottom 2 m of the well consists of thick shales, some of which are interbedded with siltstones, some silty and shaley sandstones, and a few small limestone intervals near the very bottom (Appendix B: Core Logs). There is then a brief interval that contains heterolithic sandstone-mudstone bedding and multistory sandstones. A couple small sandstone sections that are 3 cm and 18 cm thick, respectively, follow the multistory sandstone, which then transition into a 34 cm section of shale with some lenticular bedding. The well then contains a section of multistory sandstones that have a plethora of mud drapes along with some
50
bioturbation and some mudstone intraclasts. The next 51 cm then consists of shale that has a few
deformation structures and some convoluted bedding. The top portion contains sandstone and a
few small 1 - 2 cm shale intervals. These sandstones contain mud chips and mudstone intraclasts.
The bottom portion of the well coarsens-upwards, then fines-upwards as it transitions into the
middle portion of the well. The middle section of the well coarsens-upwards until it reaches the
bottom part of the top-third of the well. The well then fines-upwards for about 1.25 m, and then
coarsens-upwards for 0.75 m. The overall thickness of the well is 5.59 m. Depth of this well
begins at -2900’ and ends at -2921’.
Well 2980
In well 2980 (drilled in Vinton County), the bottom 75 cm of this well is almost completely shale with some interbedded siltstone (Appendix B: Core Logs). The heterolithic mudstone- siltstone then transitions into heterolithic mudstone-sandstone. There are a few deformation structures in this region. Mud becomes less prevalent toward the top of the well as the lithology shifts to multistory sandstones with mud drapes separating the sandstone bodies. The upper part of the well contains multistory sandstone bodies, some of which are bioturbated, and numerous mud drapes. The overall thickness of the well is 4.77 m. Death of this well begins at -2820’ and ends at -2839’.
Well 2965
In well 2965 (drilled in Vinton County), heterolithic sandstone-mudstone bedding is located at the bottom of the well (Appendix B: Core Logs). Above this lithology is planar laminated sandstone, which is separated by 3 – 9 cm intervals of shale. A section of heterolithic mudstone- siltstone overlays the laminated sandstone region. This then transitions into a sandstone lithology with frequent mud drapes, bioturbation, and mudstone intraclasts. The well then contains 47 cm
51 of indistinctly cross-bedded sandstone, followed by 6 cm of shale, then 25 cm of indistinctly cross-bedded sandstone. The well then transitions into sandstones with numerous mud drapes, some deformation structures, and mudstone intraclasts. Thin shale intervals are also present in this section, some of which contain lenticular bedding. Bioturbation is heavy in some areas. The very top of this well consists of a muddy sandstone and fissile shale. The overall thickness of the well is 8.51 m. Depth of this well begins at -3143’ and ends at -3177’.
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Figure 14. Well log of well 2866 (-758 m to -760 m).
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Figure 15. Well log of well 2866 (-760 m to -762.6 m).
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Figure 16. Well log of well 2941 (-943.5 m to -947.5 m).
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Figure 17. Well log of well 2942 (-984 m to -987.5 m).
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Figure 18. Well log of well 2943 (-884 m to -888 m).
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Figure 19. Well log of well 2943 (-888 m to -889.8 m).
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Figure 20. Well log of well 2980 (-859.5 m to 863.5 m).
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Figure 21. Well log of well 2980 (-863.5 m to -863.8 m).
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Figure 22. Well log of well 2965 (-958 m to -962 m).
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Figure 23. Well log of well 2965 (-962 m to -966 m).
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Figure 24. Well log of well 2965 (-966 m to -967.2 m).
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Lithology
Sandstone
Sandstones in the “Clinton Sandstone” range from fine-grained to medium-grained with a
variety of sedimentary structures including planar-lamination, cross-bedding, trough cross-
bedding, massive bedding, and different tidalite bedding such as heterolithic sandstone-mudstone
and mud drapes. The rhythmic facies associated with the “Clinton Sandstone” wells include
flaser, wavy, and lenticular bedding. Compositionally, the sandstone ranges from light grey, to
yellow, to red, and are calcareous and argillaceous quartz arentie. Some bioturbation is present,
but not common for the sandstone lithology in the “Clinton Sandstone”. There are four natural
fractures observed in a sandstone bodies from wells 2942, 2941, and 2965. Figure 24 shows a
typical photomicrograph of sandstone from the “Clinton Sandstone” core observed. Figure 25
shows an area of the “Clinton Sandstone” with an abnormal amount of calcite cement.
Siltstone
Siltstone is uncommon and mainly found as planar-laminated or rhythmic planar-laminated
siltstone-mudstone in well 2965. Other areas containing silt are part of carbonate intervals. Of
the planar laminated and rhythmic siltstones, the grains were sub-rounded to sub-angular, well
sorted, quartz siltstones. These siltstones also contain some feldspars and mud chips. Siltstone is
not nearly as common as sandstone and tends to appear more toward the bottom of a well.
Limestone
The limestone found in the cores studied is rare and only appears in small intervals in wells
2943 and 2942. It is surrounded by sandstone and is typically about 3 - 5 cm thick. This
limestone is fine-grained, poorly sorted, massive, and contains bryozoans, brachiopod spines, ooids, silt-sized quartz, and is held together mainly by micritic cement (Figures 26 and 27).
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Figure 25. A photomicrograph showing the tight nature of the grains, as well as quartz overgrowth. QG = quartz grain, F = feldspar grain, QO = quartz overgrowth. Silica cement is holding these siliciclastic grains together. The porosity of this particular area is poor since there is very little pore space available at all.
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Figure 26. A photomicrograph showing an area with calcite cement. QG = quartz grain, CC = calcite cement. Silica cement is also present in this picture between quartz grains. This siliciclastic photomicrograph also shows very little pore space available.
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Mudstone
Mudstone is the second most common lithology in the “Clinton Sandstone.” It appears as massive, bioturbated, or as heterolithic sandstone-mudstone or siltstone-mudstone. Mudstone found in the cores studied is interpreted as shale. Mud drapes and mud chips are fairly common in sandstone bodies. Figure 28 shows an example of a double mud drape found in a photomicrograph. Mud drapes found in a sand body typically indicates tidal influence.
Lithofacies Analysis
Sixteen lithofacies are found in wells 2866, 2941, 2942, 2943, 2980, and 2965. A code was created for each lithofacies that contains both an upper case and a lower case letter. The upper case letter determines the lithology (e.g., L represents limestone, M represents mudstone), and the lower case letter signifies the sedimentary structure (e.g., Sth represents trough cross- bedding). The 16 different lithofacies are shown in Table 10 and the legend for these lithofacies is shown in Appendix B: Core Logs.
Each lithofacies then has the potential to be grouped into an assemblage, which is used to help assign an environment that most likely produced that facies. After describing each lithofacies and assigning them to assemblages, it was possible to interpret the depositional environment. Not all cores have the same depositional environments and most actually have more than one environment present.
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Figure 27. A photomicrograph of a small limestone interval. B = bryozoan, Q = quartz grain, MC = mud chip. Quartz grains, mud chips, and bryozoans are present within this crystalline texture. Porosity is poor within this photomicrograph because of the varying clast sizes and micrite cement.
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Figure 28. A photomicrograph of a brachiopod spine and surrounding bryozoans. This crystalline texture is tightly compacted and voids are filled with micrite cement.
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Figure 29. A photomicrograph showing double mud drapes in a sandstone body. MD = mud drape. This clastic texture is well compacted and very little pore space is available. The mudstone present is also filling pore space and potentially creating a seal within this sandstone.
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Table 10. Lithofacies table consisting of the facies seen in core numbers 2866, 2941, 2942, 2943, 2980, and 2965.
Lithofacies Lithology Sedimentary Interpretation Structures Sth Sandstone Trough cross-bedded, Migration of dunes shale partings with periods of low current conditions Sc Sandstone Planar-tabular cross- Migration of dunes bedding Smi Sandstone Massive, mudstone Erosive surface intraclasts Sm Sandstone Massive Deposition of sand with increased sediment supply Sl Sandstone Planar lamination Upper plane bed
SSl Siltstone Planar lamination Upper plane bed SMk Heterolithic Lenticular bedding Tidal rhythmite with sandstone-mudstone ripple marks SMl Heterolithic Planar lamination Tidal rhythmite sandstone-mudstone SMf Heterolithic Flaser bedding Tidal rhythmite with sandstone-mudstone ripple marks SMw Heterolithic Wavy bedding Tidal rhythmite with sandstone-mudstone ripple marks SMd Heterolithic Ball-and-pillow Heavier sediment sandstone-mudstone structure moved through unconsolidated layer SSMl Heterolithic siltstone- Planar lamination Tidal rhythmite mudstone SSMb Heterolithic siltstone- Bioturbation Tidal rhythmite with mudstone organism activity in unconsolidated material Mmb Mudstone Bioturbation Organism activity in unconsolidated material Mm Mudstone Massive Deposition of mud with increased sediment supply Lm Limestone Massive Marine shelf
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Planar-Tabular Cross-bedded Sandstone (Lithofacies Sc)
Lithofacies Sc is found in all of the wells studied and it the most common type of bedding
(Figure 18). Lithofacies Sc is typically light to dark gray in color. It is hard to distinguish from
massive bedded sandstones because the cross-beds are difficult to see. Lithofacies Sc commonly
contains other sedimentary structures including mud drapes, mud chips, or mudstone intraclasts.
A section of this bedding is over 2.5 m thick in well 2491. Other sections can be as small as 1 cm
and are usually separated by mud drapes.
Migrating dunes will produce cross-bedding. In a storm-dominated shoreface, cross-beds can be distrupted and destroyed by planar-laminated and hummocky-stratified sandstones (Walker
and Plint, 1992). Whereas planar tabular cross-beds are more common in shoreface deposits where there is longshore current.
Trough Cross-Bedded Sandstone With Shale Partings (lithofacies Sth)
Lithofacies Sth can be found in all wells studied. Some occurrences of mud drapes consist of
a single mud drape in a large sandstone section, while other instances contain several in a small
area (Figure 19). After observing the thin sections under the microscope, it was apparent that
double mud drapes were present in a few areas, which would be evidence for tidal influence.
These mud drapes are very thin and typically about 0.1 - 0.2 cm thick. Most mud drapes found in
these wells are present in a sandstone body.
Mud drapes found in a sandy environment are a good indication that slack water intervals
occurred. Small and isolated shale partings being deposited would indicate that very little mud
was in suspension during the slack water conditions. In the “Clinton Sandstone,” lithofacies Sth
is indicative of intervals of sand and mud deposition with most of the mud being eroded away
during the next tidal cycle.
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Figure 30. Planar-tabular cross-bedded sandstone (lithofacies Sc) from well 2866. This particular interval is about 0.8 m in its entirety. Herringbone cross-bedding is not present in this interval so the current was flowing in one direction. These cross-beds are difficult to see but are 2-D. Bottom scale bar is in centimeters.
Figure 31. Trough cross-bedded sandstone with shale partings (lithofacies Sth) from well 2943. This interval of trough cross-bedding is about 0.4 m in length. Current flow for this interval was unidirectional and the ripples are 3-D. Bottom scale bar is in centimeters.
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Massive Sandstone with Mudstone Intraclasts (Lithofacies Smi)
Lithofacies Smi consists of massive, fine-grained, well sorted, sub-rounded quartz arenite
with mudstone intraclasts. The color of these sandstones is typically light gray, but can also be
red. The size of an individual mudstone intraclast is generally < 1 cm (Figure 20).
Intraclasts can be formed by fragmentation or erosion of cohesive sediments in a high energy
environment. Such environments may include distributary channels, tidal zones, or storms. The
intraclasts are carried by currents and usually amass close to their place of origin. In the “Clinton
Sandstone,” lithofacies Smi is most likely part of a distributary channel that was subject to rapid
deposition, while mudstone intraclasts moved as bedload.
Massive Sandstone (Lithofacies Sm)
Lithofacies Sm is one of the hardest lithofacies to decipher. It looks very similar to other kinds of cross-bedding since cross-bedding in these wells is hard to decipher. The massive
bedding is fine-grained, well sorted, sub-angular quartz arenite. Most of the massive bedding is
located in well 2941 and can be as thick as 1.5 m with only sparse mud chips, mud drapes, and
mudstone intraclasts interrupting the massive sandstone bodies (Figure 21). It is also possible that a well-sorted, cross-bedded interval can appear to be massive,
The development of massive beds can result from a number of scenarios. A common reason is the rapid deposition of homogenous sediments. Examples of this include grain flows, mud flows, and the lower part of turbities (Boggs, 2001). At times, primary sedimentary structures can be destroyed by intense bioturbation or fluid escape. These destroyed structures can become massive. Liquefaction of sediment due to sudden shock can also be a means of destroying
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Figure 32. Massive sandstone with mudstone intraclasts (lithofacies Smi) and shale partings from well 2941. This interval is about 0.1 m in length. Current flow appears to be unidirectional. Scale bar on the bottom is in centimeters.
Figure 33. Massive sandstone (lithofacies Sm) from well 2941. This interval of massive sandstone is about 1.5 m in length and was most likely deposited due to rapid deposition. Scale bar on the bottom is in centimeters.
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original structures to produce massive bedding. In the “Clinton Sandstone,” lithofacies Sm is part
of a distributary channel deposit due to rapid sediment deposition.
Laminated Sandstone (Lithofacies Sl)
Lithofacies Sl consists of planar laminated fine-grained, well sorted, sub-angular to sub- rounded quartz arenite. These beds are generally thin, with most being only a few centimeters, but one section in particular is 18 cm thick. Laminated sandstones are only found in well 2965 and typically found between shale intervals (Figure 22).
A number of mechanisms can produce planar-lamination. Shallow flow in a small flume caused by downstream movement of very low, depth limited, current ripples and slow aggradation can produce planar-lamination (McBride et al., 1975). Fallout of suspended sediment on a planar surface in the occurrence of a weak current may also produce planar- lamination. Planar-laminated sandstone may be part of a tempestite sequence that was deposited by oscillatory currents or from a waning storm (Walker and Plint, 1992) or an upper flow regime plane bed.
Laminated Siltstone (Lithofacies SSl)
Lithofacies SSl is a very fine-grained, well sorted, sub-angular, quartz arenite (Figure 23).
This lithofacies is not common in the cores studied, but can be as thick as 5 cm. It is mainly found in well 2965 and is usually overlain and underlain by heterolithic sandstone-mudstone bedding.
Siliciclastic silts can be windblown into different areas and deposited if the energy of that environment is low enough. The planar features of these deposits show that the current was relatively slow and the silt was deposited in a rhythmic fashion, which would indicate some sort
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Figure 34. Laminated sandstone (lithofacies Sl) from well 2965. This interval is about 0.4 m in length. These laminated sandstones were likely rhythmically deposited in an upper flow regime plane bed. Scale bar on the bottom is in centimeters.
Figure 35. Laminated siltstone (lithofacies SSl) from well 2965. The interval shown is about 0.1 m in length. This example of laminated siltstone was deposited rhythmically in a prodelta environment. Scale bar on the bottom is in centimeters.
77
of a tidal interaction. In the ‘Clinton Sandstone,” it is possible that lithofacies SSl was deposited
in a prodelta environment.
Heterolithic Lenticular Bedded Sandstone-Mudstone (Lithofacies SMk)
Lithofacies SMk consists of ripple laminated or lenticular bedded fine-grained, sub rounded,
quartz arenite and interbedded mudstone (Figure 25). The mudstones present are in the form of
mud drapes and have an average thickness of < 0.5 cm. The sand ripples are isolated in the mud
matrix. Lithofacies SMk regularly alternates with lithofacies SMl, but can also be found near
lithofaices SMw. Average thickness of lithofacies SMk is about 3 cm.
The sedimentary structure of lenticular bedding consists of mud drapes and alternating sand
ripples with a larger quantity of mud compared to sand. The sand ripples traveled over a bed of
mud and were then deposited and covered by another layer of mud. Most sand lenses are
isolated, but they can be connected. Lithofacies SMk is interpreted as a fluctuating tidal flow that produces sandy ripples in an environment that is dominated by mud. In the “Clinton Sandstone,” lithofacies SMk is interpreted to be deposited in a mud flat of the intertidal zone.
Heterolithic Flaser Bedded Sandstone-Mudstone (Lithofacies SMf)
Lithofacies SMf consists of flaser bedded fine-grained, sub rounded, quartz arenite and mud
(Figure 26). Lithofacies SMf is present in well 2965 in several different sections. These beds contain thin mud layers present in the trough of a sand ripple. This bedding is typically located between lithofacies Sc and can be as thick as 18 cm.
Lithofacies SMf will typically form in a fluctuating tidal environment that favors deposition of sand and silt over mud. Intertidal flats will commonly contain flaser bedding structures. It is formed when thin mud laminae alternate with sandy ripples during slack water conditions
(Reineck and Wunderlich, 1968). The amount of mud in a deposit represents the amount of mud
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Figure 36. Heterolithic sandstone-mudstone with lenticular bedding (lithofacies SMk) from well 2866. This interval shown is about 0.06 m in length. Lenticular bedded facies are likely deposited in a mud flat environment. Scale bar on the bottom is in centimeters.
Figure 37. Heterolithic sandstone-mudstone with flaser bedding (lithofacies SMf) from well 2965. This particular interval is about 0.2 m in length. Flaser bedded deposits are likely formed in a sand flat environment. Scale bar on the bottom is in centimeters.
79
that was in suspension. Some of the mud deposited during the period of slack water can be
partially eroded in the next cycle, which can leave a thin layer of mud in the troughs. If more
mud is introduced to the environment, then either wavy bedding or lenticular bedding may be
produced. The presence of lithofacies SMf generally indicates deposition in a sand flat. In the
“Clinton Sandstone,” lithofacies SMf is interpreted to be deposited in a sand flat environment.
Heterolithic Bedding with Wavy Bedding (Lithofacies SMw)
Lithofacies SMw consists of wavy bedded fine-grained, sub rounded, quartz arenite and
interbedded mudstone (Figure 27). Average thickness of the mud layer in lithofiaces SMw is
generally < 1 cm. Lithofacies SMw is not as common as lithofacies SMl, but it can be found in
wells 2943, 2980, and 2965 around the alternating sandstone and mudstone intervals. The wavy
bedding composition is about half sandstone and the other half mudstone that does not show
planar-lamination. The average thickness of lithofacies SMw is about 2 cm.
Heterolithic wavy beds can be formed in fluctuating high and low energy environments with tidal conditions that favor neither sand nor mud deposition. A temporary increase of tidal currents and an increase of mud drapes due to wave activity explain the presence of wavy-beds in between planar rhythmites. An increase in sand in this type of environment would produce flaser bedding, while an increase in mud would produce lenticular bedding. Combinations of high energy conditions and slack water conditions exist in a mixed flat environment where such deposition is related to changes in bottom current velocity during a tidal cycle (Klein, 1977). In the “Clinton Sandstone,” lithofacies SMw is interpreted to be deposited in a mixed flat region.
Heterolithic Bedding with Ball and Pillow Structure (Lithofacies SMd)
Lithofacies SMd consists of both mudstone and sandstone (Figure 28). The sand present is fine-grained, sorted, sub-rounded, quartz arenite. This lithofacies is not all that common in the
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Figure 38. Heterolithic sandstone-mudstone with wavy bedding (lithofacies SMw) from well 2943. This particular section is about 0.1 m in length. Wavy bedding is likely deposited in a mixed flat region. Scale bar on the bottom is in centimeters.
Figure 39. Heterolithic sandstone-mudstone with ball-and-pillow structure (lithofacies SMd) from well 2980. This section shown is about 0.05 m in length. Ball-and-pillow structures are likely the result of rapid deposition in a distributary mouth bar environment. Scale bar on the bottom is in centimeters.
81 wells studied, but it does appear near the bottom of well 2980 in a few sections. The thickness of these intervals ranges from just 2 cm to about 6 cm. Lithofacies SMd is typically overlain and underlain by heterolithic sandstone-mudstone bedding.
Lithofacies SMd typically forms in unconsolidated sediments. In the case of this lithofacies, a sand layer sank into an underlying mud layer and formed several sub-rounded and elongated structures. For this process to happen, the underlying mud layer must be cohesive and the overlying sand layer must have a higher density. In the “Clinton Sandstone,” lithofacies SMd most likely formed in a distributary mouth bar environment due to rapid sediment deposition in a delta front environment.
Heterolithic Laminated Sandstone-Mudstone (Lithofacies SMl)
Lithofacies SMl consists of planar laminated, fine-grained, sub rounded, quartz arenite interbedded with mud (Figure 29). The thickness of the mud layers is usually < 1 cm. Lithofacies
SMl is usually overlain by lithofacies Sth and underlain by lithofacies Sc.
Lithofacies SMl is interpreted to be deposits from tidal rhythmites in the intertidal zone.
These planar-laminated tidal rhythmites are bundles of laterally and/or vertically accreted, laminated to thinly bedded fine-grained sandstone, siltstone, and mudstone of tidal origin that show rhythmic change in laminae thickness and grain size (Mazumder and Arima, 2004). The alternating layers of sand and mud seen in lithofacies SMl are deposited by the change in current speed during deposition. Mud will be deposited during slack water conditions, while coarser material is deposited during maximum energy conditions, approaching low or high tide (James and Dalrymple, 2010). In the “Clinton Sandstone,” lithofacies SMl is interpreted to be deposited in an interdistributary bay environment.
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Figure 40. Heterolithic sandstone-mudstone with planar lamination (lithofacies SMl) from well 2866. This particular interval is about 0.1 m in length. Heterolithic sandstone-mudstone bedding in this project is typically formed in either interdistributary bay or distributary mouth bar environments. These alternating beds were formed in a rhythmic fashion during deposition. Scale bar on the bottom is in centimeters.
Figure 41. Heterolithic laminated siltstone-mudstone (lithofacies SSMl) from well 2943. This interval shown is about 0.35 m in length. Laminated siltstone-mudstone bedding is typically formed in a prodelta environment. Scale on the bottom is in centimeters.
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Heterolithic Laminated Siltstone-Mudstone (Lithofacies SSMl)
Lithofacies SSMl consists of planar laminated, fine-grained, sub angular, quartz arenite with
alternating mud layers (Figure 43). The thickness of the mud is typically < 1 cm. Lithofacies
SSMl is typically overlain by lithofacies SMl and is underlain by lithofacies Mm. This
lithofacies is uncommon and generally appears near the bottom of cores.
Lithofacies SSMl is interpreted to be deposits in a more distal setting than lithofacies SMl
which is created in the intertidal zone. The thin layers of siltstone and mudstone are deposited
cyclically and can be seen when looking at the laminae thickness and grain size. Even with a
slight current, it is not easy to deposit silt or mud. Because of this, it is more likely that
lithofacies SSMl was deposited in a prodelta environment where finer sediment stays in
suspension and is eventually deposited in a distal setting. In the “Clinton Sandstone,” lithofacies
SSMl is interpreted to be deposited in a prodelta environment.
Heterolithic Siltstone-Mudstone with Bioturbation (Lithofacies SSMb)
Lithofacies SSMb is only found near the bottom of well 2943. It appears in several smaller
intervals that range from 1 - 8 cm. This lithofacies contains siltstone and mudstone like
lithofacies SSMl but the sediments have been mixed together because of bioturbation (Figure
33). Since this lithofacies is found near and at the bottom of well 2943, it does not have another
lithofacies beneath it, but it is overlain by lithofacies SSMl.
Lithofacies SSMb is interpreted to be deposits from a more distal environment, like a prodelta. Silt and mud are typically deposited furthest from the shore because current and wave activity keep them in suspension. A prodelta environment typically does not have currents and wave activity is generally minimal. Most organisms favor a calmer environment so numerous
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Figure 42. Heterolithic siltstone-mudstone with bioturbation (lithofacies SSMb) from well 2943. This interval of siltstone-mudstone is about 0.15 m in length. This facies is similar to SSMl but is bioturbated before lithification. Scale bar on the bottom is in centimeters.
Figure 43. Massive mudstone with bioturbation (lithofacies Mmb) from well 2943. The interval shown is about 0.1 m in length. This type of mudstone is deposited and then bioturbated before lithification. The presence of mudstone usually indicates a period of slack water conditions. Scale bar on the bottom is in centimeters.
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burrowing creatures may be present. These organisms will move through the unconsolidated
sediments and mix the mud and silt together. In the “Clinton Sandstone,” lithofacies SSMb is
interpreted to be deposited in a prodelta environment.
Massvie Mudstone with Bioturbation (Lithofacies Mmb)
Lithofacies Mmb is not common among the cores studied and appears near the bottom of well
2943 (Figure 30). It ranges in thickness from 1 - 6 cm and is overlain by lithofacies SMl and underlain by lithofacies Sc. A noticeable difference between this lithofacies and lithofacies
SSMb is that there is much more mud present in lithofacies Mmb.
Massive mudstone can appear to be completely uniform (one color and lithology) or can be bioturbated like lithofacies Mmb. The massive mudstones found in the cores studied represented the former and were classified as lithofacies Mm. Mudstones that were not uniform and contained obvious bioturbation were labeled Mmb. Lithofacies Mmb is interpreted to be deposited in a delta front environment. Reasons for this include the lithofacies that were found above and below it. Above was lithofacies SMl, which is common in a delta front environment, and below consisted of several small planar tabular sandstone bodies that contain shale partings,
as well as a couple thin shale intervals, which could also be related to a delta front environment.
Massive Mudstone (Lithofacies Mm)
Lithofacies Mm is fairly common among the cores studied. It is present in large bodies that
can be as thick as 0.75 m or as thin as about 2 cm (Figure 31). Mudstone is generally more
common near the bottom of wells, but it can be found in the middle of wells separating sandstone
bodies, and near the top of wells 2866, 2941, 2942, 2943, 2980, and 2965. The main sedimentary
structure present is massive bedding. In a few instances, there are small sandstone or siltstone
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Figure 44. Massive mudstone (lithofacies Mm) from well 2941. This interval of mudstone is 0.2 m in length. Intervals of mudstone typically indicate a period of slack water conditions. Scale bar on the bottom is in centimeters.
Figure 45. Massive limestone (lithofacies Lm) from well 2943. This interval of limestone is about 0.05 m in length. This is a bioclastic deposit that was likely ripped up and carried to the area by a storm. Scale on the bottom is in centimeters.
87 beds that can be found in a large mudstone body. The contact between a mudstone bed and another type of bed is generally sharp.
Massive mudstones can indicate deposition of homogenous mud in low-energy environments.
Slack water conditions can occur after a flood or ebb during the pause or before the current is reserved. Mud present between sandstone beds indicates alternating events of transport and deposition. In the “Clinton Sandstone,” lithofacies Mm is interpreted as a significant slack water event.
Massive Limestone (Lithofacies Lm)
Lithofacies Lm consists of massive, fine-grained biomicrite that is well compacted (Figure
34). Other components found under the microscope include brachiopod spines, bryozoans, ooids, fine-grained quartz and silt-sized quartz. Intervals of lithofacies Lm are small and uncommon in the wells observed. These packages can only be found near the bottom of wells 2942 and 2943 and range in size from 2 cm to 4 cm. They are typically overlain and underlain by mudstone.
Micrite is “lime mud” that is dense and dull-looking under the microscope. Most micrite observed is formed from the breakdown of calcareous algae skeletons (Prothero and Schwab,
1996). In the “Clinton Sandstone,” lithofacies Lm is interpreted to be part of a nearby marine shelf that was ripped up by a storm and carried to a prodelta environment.
Lithofacies Assemblages
Lithofacies associations are a key aspect to identifying depositional environments since single lithofacies are not unique when evaluating depositional processes. It is not uncommon to have a single lithofacies that can be produced from several different processes. When individual lithofacies are grouped together they can be used to interpret depositional environments. A
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lithofacies assemblage can be described as a number of facies that are related and have some
environmental importance when grouped together (James and Dalrymple, 2010).
Tidal Inlet Channel
A tidal inlet channel is an area where sandy deposits are found in ebb-tide and flood-tide
deltas. A typical facies assemblage showing a tidal inlet channel would consist of massive
sandstone, planar-tabular cross-bedded sandstone, sandstone with intraclasts, and herringbone
cross-bedded sandstone. The tidal inlet channels in this study are typically about 10 - 20 cm, but
the example at the bottom of well 2941 is about 2 m thick (Figure 35). Tidal inlet channels found
in these “Clinton Sandstone” wells do not show any herringbone cross-bedding, which means
that the flow was unidirectional. The most common lithofacies in these assemblages is lithofacies
Sm, but lithofacies Sc and Smi are also present in nearly all observed tidal inlet channel
assemblages.
Tidalites
For this study, the tidalite assemblage includes heterolithic lenticular bedded sandstone-
mudstone (lithofacies SMk), heterolithic flaser bedded sandstone-mudstone (lithofacies SMf),
heterolithic planar laminated sandstone-mudstone (lithofacies SMl), heterolithic wavy bedded sandstone-mudstone (lithofacies SMw), and heterolithic sandstone-mudstone with ball-and- pillow-strucutres (lithofacies SMd). Tidalites can be found in well 2980 and 2965. Figure 36 shows a tidalite assemblage in well 2980.
A typical tidalite assemblage will encompass all of the deposits of a tidal current. Lenticular bedding represents an episode where the current is slight and mud is deposited along with a small
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Figure 46. Tidal inlet channel assemblage in well 2941.
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Figure 47. Tidalite assemblage in well 2980.
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amount of sand. The opposite of this would be flaser bedding, where the current is stronger and
more sand is moved and deposited along with a small amount of mud. The intertidal zone can be
broken down into a sand, mud, and mixed flat area. These areas are determined by the amount of
sediment present. Monthly tidal patterns can also be seen by observing differences in the
thickness of sand bodies present. The spring-neap cycle has a length of 14.77 days and will
produce 28 semidiurnal cycles. A spring tidal cycle contains thicker muds than that of the neap
cycle.
Distributary Mouth Bars
Distributary mouth bars can be found in the lower delta plain area of a delta (Figure 37).
These features are typically formed when sediment is deposited entering a river basin. The
reason for deposition in distributary mouth bars can be related to hypopycnal flow. This
particular type of flow causes bedload deposition at the channel mouth because the river water
moving through the distributary channel is less dense than the ambient seawater. When the two different types of water meet, a surface plume will form and the suspended sediment will be dispersed by waves, tides, or current. The sediment can be carried as far as 100 km offshore.
The main lithology found in a distributary mouth bar will consist of heterolthic sandstone- mudstone. The amount of sand versus mud can vary greatly. More sand present will create flaser bedding, which is mud flocculates in a sand layer. If more mud is present in the environment, then lenticular bedding will form, which can be described as sand lenses in a mud layer. It is also possible to have an equal amount of both sand and mud, which will generate wavy bedding.
Deformational structures can also be an indicator of a distributary mouth bar environment. These
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Figure 48. Distributary mouth bar deposit from well 2980.
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Figure 49. A distributary mouth bar deposit showing lithofacies SMd and SMk. Core picture is taken from well 2980.
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Point Bar Sequences
structures are created when a heavier lithology sinks through a softer and less dense lithology.
The overall trend for this type of deposit will show a coarsening-upward sequence.
Meander point bar deposits can be found in distributary channels (Figure 38). These deposits are found on the opposite side of the channel from a cutbank, where a river meanders or creates
an angle where the flow of water is no longer flowing straight. The change in direction produces
an area where velocity is faster along the cutbank and slower along the point bar. Because of this
velocity difference, the sediment deposited here is generally well sorted and mainly sand.
Sediment present in a meander point bar deposit can vary but it will typically consist of sand.
The size of the sand will depend on the overall capacity of the river. Mud also has the potential
to be deposited in a meander point bar. Evidence of this can be seen in Figure 48. Lithofacies Sc
and Sth are the lithologies present in meander point deposits for this study. Meander point bar
deposits are also known to show a fining-upwards sequence.
Trace Fossils
Only one type of trace fossil was identifiable in the wells described. However, this area of the
“Clinton Sandstone” contains a moderate amount of bioturbation (10% - 50%). Bioturbation can be seen in all the wells studied and the amount of it varies from well to well. This bioturbation present may have destroyed previous trace fossils located in these “Clinton Sandstone” wells.
The only obvious trace fossil located within the well samples was Ophiomorpha. This trace fossil is likely created from a bivalve and ranges from Late Ordovician to Early Silurian in age.
The remains should resemble a boring in the rock shaped like a tube. The trace fossil itself, located in well 2866, is about 1 cm in length and has been filled in with sand (Figure 39).
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Figure 50. Meander point bar deposit from well 2866.
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Figure 51. A meander point bar deposit showing lithofacies Scu with mud chips. Core picture is taken from well 2866.
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Figure 52. An example of Ophiomorpha from well 2866. The bottom scale bar represents centimeters.
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Core Logs Correlating to Geophysical Logs
Of the six wells observed, described, and photographed at the H.R. Collins Laboratory in
Delaware, Ohio, only four of the wells had a corresponding geophysical log. This section of this thesis will look at how well the cores matched up with their geophysical log readings.
Well 2866
Well 2866 is from the Rush Creek Township, located in Fairfield County, Ohio (Figure 40).
This well contains a meander point bar deposit, planar-tabular cross-bedding, heterolithic
sandstone-mudstone bedding, mudstone intraclasts, mud chips, shale partings, and bioturbation.
The bottom 1.5 m contains mainly planar-tabular cross-bedded sandstone with occasional shale
partings. These sandstones coarsen-upwards for about ½ m before fining-upwards for about 2 m.
The core to gamma-ray comparison at the bottom of the well is consistent. The middle of the
well shows a small coarsening-upward sequence, which contains planar-tabular sandstone at the
bottom, which then transitions into heterolithic sandstone-mudstone bedding. This small
coarsening-upward sequence quickly changes back to a fining-upward sequence, which
continues to the top of the well. The fining-upward sequence of the core near the top of the well
matches the geophysical log trend. The fining-upward sequence shows the transition from
planar-tabular cross-bedded sandstones to heterolithic sandstone-mudstone bedding. Overall, the
core sample and the gamma-ray from the corresponding geophysical log match up well.
Well 2941
Well 2491 is from the Jackson Township, located in Perry County, Ohio (Figure 41). This
well contained a large section of cross-bedded and massive sandstones with very little mudstone
interruption, occasional mudstone intraclasts, mud chips, shale partings, and bioturbation. The
bottom and middle portion of the well contains thick, massive and cross-bedded sandstones. The
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sandstone at the bottom shows a coarsening upward sequence, which is consistent with the other
“Clinton Sandstone” wells studied because there is typically shale located beneath. Approaching
the middle of the well, the sandstones then begin to fine-upwards. This is consistent with the
gamma-ray on the geophysical log since the upper portion of the well contains some mudstone,
mud chips, and shale partings. The top of the well contains some mudstone, and other mud
structures such as mudstone intraclasts, mud chips, and shale partings. The region of the well
shows a small coarsening-upward sequence when planar-tabular cross-bedded sandstones are
encountered. However, they then transition back to a fining-upward sequence at the very top of
the well due to mud chips and heterolithic sandstone-mudstone bedding. Overall, this core
sample is consistent with the corresponding gamma-ray reading from the geophysical log.
Well 2943
Well 2943 is from the Reading Township, located in Perry County, Ohio (Figure 42). This well contains mostly heterolithic sandstone-mudstone bedding, but also possesses planar-tabular cross-bedded sandstone, mudstone intraclasts, shale partings, bioturbation, and deformation structures. The bottom 1 m of the well consists of heterolithic siltstone-mudstone which transitions into limestone and heterolithic sandstone-mudstone. This portion of the well reflects the gamma-ray of the corresponding geophysical log by showing a coarsening-upward sequence.
The middle of the well shows a fining-upward sequence consisting of interbedded sandstone and thin mudstone layers, which transition into heterolithic sandstone-mudstone bedding. The corresponding gamma-ray also shows this change in lithology. However, the top of the well does not reflect the geophysical log as well as the bottom and middle portions. There is a unit of heterolithic sandstone-mudstone bedding that is about 2 m thick, which does not match up with
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the gamma-ray reading. Missing sections of core may be the reason why the top portion of the
gamma-ray and core sample do not match up.
Well 2980
Well 2980 is from the Swan Township, located in Vinton County, Ohio (Figure 43). This well
contains mainly heterolithic bedding, but also consists of planar-tabular sandstone bodies and
mudstone. Other features include deformational structures, mudstone intraclasts, shale partings, and bioturbation. The bottom 1 m of the well contains a thick mudstone unit that transitions into lenticular bedding and sandstone. The geophysical log in this area shows a fining-upward sequence, which does not corresponds to the coarsening-upward sequence the lithologies show in the core sample. The next 2 m of core shows heterolithic sandstone-mudstone bedding that starts as mainly flaser bedding and transitions into wavy and lenticular bedding. The gamma-ray does reflect this change by showing a fining-upward sequence. The top 2 m of the well shows a transition from lenticular bedding to wavy bedding, to flaser bedding, and planar-tabular cross-
bedded sandstone. This change in lithology is shown on the corresponding gamma-ray reading
with a coarsening-upward sequence.
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Figure 53. Well 2866 core log versus geophysical log comparison.
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Figure 54. Well 2941 core log versus geophysical log comparison.
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Figure 55. Well 2943 core log versus geophysical log comparison.
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Figure 56. Well 2980 core log versus geophysical log comparison.
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Basin Mapping
A total of 16 geophysical logs were analyzed to better understand the architecture, structure, and distribution of the “Clinton Sandstone” in the study area. Gamma-ray logs were the main data source used to complete correlations and determine depth, as well as thicknesses for each geophysical log. For the purposes of this study, the geophysical logs were used to create a northwest-southeast and a northeast-southwest litho-correlation profile, an isopach map, and a 3-
D subsurface wireframe map. Figure 55 has been constructed to make Figures 57 and 58 easier to read and comprehend.
Litho-Correlation Profiles
The two main lithologies in the “Clinton Sandstone” that need to be accounted for consist of sandstone and mudstone. Two other lithologies (siltstone and limestone) that were described in the lithology section of this thesis are scarce and typically appear near the bottom of the section.
A northwest-southeast and a northeast-southwest profile have been generated by using the gamma- ray log to identify sandstone and mudstone bodies. The log quality was fairly good for most of the logs used in this study. Because of this, it was relatively simple to correlate between logs using peak pattern matching. A reference well (#11) was used in both profiles to possibly better comprehend the geometry of the sand bodies.
Northwest-Southeast Profile
The northwest-southeast profile was made by using wells #2, #5, #7, #10, #11, #12, and #14.
The amount of sand bodies present in these wells ranges from 2 - 3 per well. If three sand bodies are present in one of the wells, then it is safe to say that the “Stray, Red, and White Clinton” are all present. However, for the geophysical logs where the well was not examined, it is difficult to say which of the three sand bodies is missing if less than three sand bodies are present.
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This profile, starting in the northwest, trends downwards until it reaches the center of Hocking
County. There is then an increase in the thickness of sandstone present which is represented by well #11. However, after this increase, it then continues to decrease along the remainder of the profile. The highest amount of sandstone available in this profile is about 10 m thick, while the smallest amount is about 4 m thick. The average amount of sandstone present throughout the northwest-southeast profile is about 6.8 m thick.
Northeast-Southwest Profile
The northeast-southwest profile was assembled by using wells #3, #4, #8, #9, #11, #13, and
#15. Three of these wells consisted of wells #4, #8, and #13, which were all examined, photographed, and described as part of this thesis. The amount of sand bodies present in these wells also ranges from 2 - 3 per well. Three of the seven wells in this profile show three distinct sand bodies, while the other four wells contain either a funnel-shaped or blocky section that appears to be representing one sand body. The sandstone thickness of the northeast-southwest litho-correlation starts out around 5 m thick and rises until it hits a maximum thickness of 11 m in southern Perry County. The profile then dips slightly and rises again to about 10 m in central
Hocking County. The remainder of the profile continues to dip downward all the way to the edge of the study area. The average thickness of the sandstone present throughout the northeast- southwest profile is about 7.1 m.
Isopach Map
The isopach map was constructed by using gamma-ray logs. Values from this map (Figure 48) show thickness variation within the “Clinton Sandstone.” On average, the thickness of the
“Clinton Sandstone” is about 6 m, but it ranges from 1 m – 11 m. The change in thickness of
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Table 11. Table showing original and new well numbers used in for figures 59 & 60.
Original Well or API # New Well or API # (Figures 57 & 58)
34045209720000 #1 34045205000000 #2 34127267800000 #3 2943 #4 34045204650000 #5 2942 #6 2866 #7 2941 #8 34127268100000 #9 34073206350000 #10 34073226160000 #11 34073206120000 #12 2980 #13 34163208730000 #14 34163202540000 #15 34163205850000 #16
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Figure 57. Northwest-southeast litho-correlation profile of the ‘Clinton Sandstone.” This figure is showing the overall deepening of the “Clinton Sandstone” in the subsurface from the northeast to the southwest. The thickness and depth of the correlations were determined by the gamma-ray readings from seven geophysical logs.
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Figure 58. Northeast-southwest litho-correlation profile of the “Clinton Sandstone.” This figure is showing erratic behavior of the “Clinton Sandstone” in the subsurface. The thickness and depth of the correlations were determined by the gamma-ray readings from seven geophysical logs.
110 the “Clinton Sandstone” in the center of the isopach map is about 4 m. The two thicker intervals could be described as channel deposits, while the other 14 points create a sloping profile away from these channels in every direction. One major trend is that the “Clinton Sandstone” becomes progressively thinner as it moves to the west, particularly the northwest. This may be symbolizing the outer limits of the “Clinton Sandstone” delta westward. The increased thickness in the center of the map may be due to an area of accumulation. Proof of this can be found in well 2941, which is located in this area of greater thickness. Well 2941 contains thick distributary channel deposits with a small amount of mudstone present. However, it is also a possibility that the large scale of the map and only 16 data points may increase the ambiguity of the results.
3-D Subsurface Wireframe Map
The 3-D subsurface wireframe map is generated by using the northing and easting coordinates from the wells and geophysical log data, as well as the sandstone thicknesses of the “Clinton
Sandstone” from the isopach map. The z-coordinate of the wireframe map shows the overall thickness of the “Clinton Sandstone,” while the x and y-coordinates shows the northing and easting extent (Figure 49). The deepest well is located in the southeastern section of the study area (API 34163208730000), where the “Clinton Sandstone” extends down to a depth of 985 m, while the shallowest well is located in the northwest quadrant of the study area (API
34045209720000) at a depth of 580 m. The depths of all wells are below mean sea level. The 3-
D subsurface wireframe map shows the overall smooth behavior of the “Clinton Sandstone” in the subsurface. Evidence of this can be seen throughout the profile with only two anomalies located in the center of the wireframe map which are uncharacteristically thick compared to the remainder of the study area. The “Clinton Sandstone” is at its thickest in the southeastern
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Figure 59. Map of the wells and geophysical logs used to create litho-correlation profiles.
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Figure 60. Location of wells with their isopach thickness values in meters.
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34045209720000 39.9
34045205000000 34127267800000
39.8
34045204650000 #2943 #2942 39.7
#2866 #2941
34127268100000 39.6
34073206350000 at tude (deg ees)
39.5 34073226160000
34073206120000
39.4 #2980
34163208730000 39.3
34163202540000 34163205850000 -82.6 -82.5 -82.4 -82.3 Longitude (degrees)
Figure 61. Isopach map of the “Clinton Sandstone” in the study area of Fairfield, Perry, and Vinton counties. Contour interval is 1 m.
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Figure 62. 3-D subsurface map of the “Clinton Sandstone” in the study area of Fairfield, Perry, and Vinton counties. The unit thins toward the west and northwest.
115 quadrant of the study area while the central portion of the study area contains the two thickest deposits (wells #9 and #11). From this central area, thicknesses of the “Clinton Sandstone” drop in every direction, but more profoundly toward the west and more so toward the northwest. The unpredictable rising and falling of the “Clinton Sandstone’s” structure, which is claimed by
Suphasin (1979), does not apply to this study area of the “Clinton Sandstone.” However,
Suphasin (1979) also explains that there is periodical absence of the three main sand bodies
(Stray, Red, and White). That assessment does apply to this thesis and can be confirmed when looking at the 6 cores that were described from the H.R. Collins Laboratory. The only well described that contained all 3 sand bodies within the “Clinton Sandstone” was well 2965.
This study area from the northern limit of Perry County to the southern limit of Vinton
County is about 8,280 km2. When looking at northwest-southeast profile, there is no net change in sandstone thickness from the northern and southern most data points. However, the “Clinton
Sandstone” does become thicker in the central-eastern region of the study area. It is likely that the central-eastern region is representing past distributary channels that were moving from the east to the west (Figure60).
Reservoir Compartmentalization
The “Clinton Sandstone” is a tight-gas formation, but it possesses other factors that can also hinder hydrocarbon production. The area studied in this thesis has identified compartmentalization at three different scales, which include micro-, meso-, and macro.
Micro-Scale
The “Clinton Sandstone’s” micro-compartmentalization is controlled mainly by the tight nature of grains and quartz overgrowths (Figure 25). The lack of space and interconnectivity of the grains poorly influences the porosity and permeability. The samples of the “Clinton
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Sandstone” studied in this thesis were comprised mainly of medium-grained quartz, but silt-sized quartz was also present in a few areas. These silt grains, like the medium-grained quartz, are tightly compacted and can also contain mud in-between grains, which can also act as a barrier and prevent or severely hinder fluid flow.
Meso-Scale
This study has uncovered a strong presence of tidal influences in the vast majority of “Clinton
Sandstone” well samples observed. Evidence of tidal influence includes the presence of flaser, wavy, and lenticular bedding, as well as mud drapes (Figure 29). These instances of mud in the cores can act as baffles, which further decrease porosity and permeability.
Of the three informal “Clinton Sandstone” beds, the “Stray Clinton” tends to contain the most mud, and therefore was subject to the highest amount of tidal influence. This assessment is consistent with a study done by Wytovich (2008), where he states that “the Stray Clinton contains the least amount of clean sand” and that “the increase of shale content causes thin discontinuous pods of sand.” This tidal influence enhances the effects of low porosity and permeability and can act as a barrier preventing fluid flow due to mud baffles. The “Red
Clinton” juxtaposes the “Stray Clinton” when comparing the amount of mud present. It is therefore appropriate to say that it experienced a lesser extent of tidal influences. Wytovitch
(2008) concludes a similar position by stating “the Red Clinton contains greater concentrations of clean sand and lateral continuity.” The “Red Clinton” unit still has low porosity and permeability due to the tight nature of grains and other features such as quartz overgrowths, but there is a better chance that compartmentalization will not be an issue.
Of the six cores studied, there were four separate small areas where natural fractures were observed. These openings range from 4 - 6 cm in length and were found in cores 2942, 2941, and
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2965 (Figure 61). The fractures documented are non-systematic and have a vertical orientation.
These fractures have also been partially filled with quartz and silica cement. The fractures are
hard to see but they do possess the possibility of increasing the permeability of the “Clinton
Sandstone.”
Macro-Scale
After analyzing the isopach map, the litho-correlation profiles, and the 3-D subsurface
wireframe map, it appears that that there is better connectivity of the sand bodies in the north-
south direction as opposed to the east-west direction. The sandstone bodies in the “Clinton
Sandstone” become much thinner as the unit moves toward the western limits of the study area
and are almost non-existent in the northwestern portion of the study area. The western edge of
the study area may be representing the ancient extent of the delta. Further analysis of the isopach
map reveals that the thickest portion of the “Clinton Sandstone” study area resides in the central-
eastern region. It is in this region where two anomalies of abnormally thick sandstone beds,
which are in close proximity, reside. The extent of the sandstone in the study area is widespread
even though thicknesses are constantly changing as well as depths. It is possible that the thin
shale intervals that typically separate the “Stray, Red, and White Clinton Sandstone” units are a
result of strong tidal events. The total amount of shale present in “Clinton Sandstone” interval is
profound, and the impermeable nature of this shale can create lateral and vertical barriers that
substantially hinder hydrocarbon fluid flow.
Reservoir compartmentalization can be summed up as individual petroleum accumulations
into a range of segregated fluid/pressure compartments (Jolley et al., 2010). This process
happens when hydrocarbons are prevented from crossing certain boundaries because of
geological and fluid dynamic factors. The two main types of boundaries are static seals and
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dynamic seals. Static seals are complete seals that can hold hydrocarbons in place for millions of
years, while dynamic seals consist of very low permeability baffles that allow hydrocarbons to
flow but at an extremely slow rate (Jolly et al., 2010). This rate is so sluggish that it significantly
affects petroleum and gas extraction and can make wells economically unfeasible.
Based on the amount of mud observed in the well samples studied in this project, it is clear that reservoir compartmentalization will most likely be a factor in this area of the “Clinton
Sandstone.” Conventional vertical drilling is not recommended because of all the various mud drapes, mud baffles, quartz overgrowths, low porosity, and low permeability samples observed during the analysis of this project. Horizontal drilling would be more economical and a technique such as fracturing would help to maximize production in this study area.
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Figure 63. An example of natural fractures in the “Clinton Sandstone.” This particular natural fracture is from well 2942.
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DISCUSSION
Depositional Environment
The “Clinton Sandstone” has been described as a deltaic deposit since the early 1900s, but what kind of a deltaic deposit the “Clinton Sandstone” represents has not been agreed on.
Previous workers have traditionally assigned the “Stray Clinton, Red Clinton, and White
Clinton” different depositional environments. Keltch (1985) concluded that the “Stray Clinton” represented a reworked delta, the “Red Clinton” resembled that of an ancient delta plain, and the
“White Clinton” was closely related to a delta front environment. Shadrach (1989) differed on his results and stated that the “Stray Clinton, Red Clinton, and White Clinton” were most closely related to a strand plain deposit, an upper delta plain deposit and a lower delta plain deposit, respectively.
This study found that not all three sand bodies within the “Clinton Sandstone” were always present. The composition of the three sand bodies also had the potential to change from one well to another. Rather than trying to give each sand body a particular environment of deposition, which sometimes changes, it is more appropriate to call this area of the “Clinton Sandstone” a tidally influenced delta that contains very few delta plain deposits, mostly delta front components, and some prodelta sequences.
Tide-Dominated Delta
Tide-dominated deltas are typically difficult to characterize. Deciding factors consist of variance in river discharge, seasonality, sediment load, grain size, and the total extent, which can be as large as 100s of kilometers (Goodbred and Saito, 2012). Because of seasonal changes, the bedding in a typical tide-dominated delta tends to be heterolithic, consisting of interbedded silts, sands, and clays. Both fining- and coarsening-upward facies sequences are also commonplace. A
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defining feature for tide-dominated deltas is the progradation of a clinoform, or “S” shaped
sedimentary deposit (Goodbred and Saito, 2012). The presence of double mud drapes also
indicates tidal influence within the “Clinton Sandstone.”
Evidence for the presence of a delta can be seen in the photographs taken of the cores studied and the lithologic sequences recorded. There are five distinct deposits that were found throughout the core samples studied and they consist of meander point bars (delta plain),
interdistributary bays (delta front), distributary channels (delta front), distributary mouth bars
(delta front), and prodelta deposits.
Meander Point Bars
Meander point bars are not particularly common in the core samples studied, but can be found
in wells 2866 and 2941. Facies in the “Clinton Sandstone” that have the potential to represent
meander point bars consist of lithofacies Sc, and lithofacies Sth. Deposits representing meander
point bars will also be absent of bioturbation, which may be due to rapid sands deposition
(Keltch, 1985). A fining-upwards sequence must also be present to denote a meander point bar
sequence. Since a fining-upwards sequence is characteristic of a decrease in energy in the
corresponding environment, it is possible to have other sediment present smaller than sand that
may settle out. Several examples of this were recorded in the photographs taken at the H.R.
Collins Laboratory (Figure 51).
Interdistributary Bays
Interdistributary bay deposits are common in the core samples studied and can be found in
wells 2866, 2943, and 2980. Facies associated with interdistributary bays include lithofacies
SMl, lithofacies SMw, lithofacies SMk, lithofacies SMf, and lithofacies SMd (Figure 52).
Interdistributary bay deposits will likely show heterolithic bedding that can be as thick as a few
122 meters (Tye and Coleman, 1989). These deposits can be either part of a coarsening-upward or fining-upward sequence. The thickness of the sequences varies from a few 10s of centimeters to over a meter.
Distributary Channels
Distributary channel deposits comprise most of well 2941. The lithology that is associated with this delta environment is lithofacies Sm (Figure 53). Distributary channels may show a wide range of shapes and sizes in a delta (Olariu and Bhattacharya, 2006). The deposits found in well
2941 consist of massive sandstones that are almost exclusively sandstone deposits. These deposits are relatively large, some are as thick as 1.5 m, and are part of an overall fining-upward sequence. Sandstones found in distributary channels may be relatively structureless and poorly stratified, which indicates rapid deposition (Gani and Bhattacharya, 2007).
Distributary Mouth Bars
Distributary mouth bar deposits can be found in well 2980. The extent of this deposit is only about 0.5 m thick and it is present towards the bottom of the well. The main lithology representing this environment is lithofacies SMd, but other lithofacies such as SMf, SMk and
SMl are also present. Distributary mouth bar deposits are likely to show heterolithic sandstone- mudstone bedding as well as a coarsening-upward sequence (Keltch, 1985). Deformational structures are also another characteristic of distributary mouth bars and several of those exist in well 2980 (Figure 54).
Prodelta
Prodelta deposits can be found near the bottom of well 2943, 2942 and 2980. These areas range in thickness from 18 cm to 1.5 m. Prodelta sediments will be muddy and typically contain bioturbation. The proximity of the deposits in the delta system can affect the features seen in a
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prodelta environment. If the sediments are rhythmically laminated, then a tidal influence may be present (Willis, 2005). Deposits that show heavy bioturbation indicate that the area is far from an active river (MacEachern et al., 2005). Preservation of sandy or silty laminae showing normal of inverse grading generally means that the deposits are close to an active river mouth. The prodelta deposits present in the wells studied show heterolithic sandstone-mudstone and mudstone- siltstone (Figure 55). Facies that are common in prodelta deposits encompass lithofacies SSMl, and SSMb. There are a few small areas that show rhythmic lamination while others contain bioturbation.
Similarities with Previous Works
This study area of the “Clinton Sandstone” involved two counties that have not been previously studied in great detail (Fairfield and Vinton counties). Perry County was researched by Msek (1973), but that study was conducted more than 40 years ago. Part of the purpose for this thesis was to compare results of previous studies with the results collected. Deltas are generally massive environments, so findings can vary greatly. However, many similarities from this study and other previous works have been observed.
The first major similarity is the overall trend of the 3-D subsurface wireframe map. This subsurface map shows the general profile of the “Clinton Sandstone” subtlety pinching out toward the west and northwest in particular. McCormac et al. (1994) conducted a study of the
“Clinton” and Medina Sandstones. He described the “Clinton Sandstone” as a unit that eventually pinches out as it moves westward into central Ohio (McCormac et al., 1994).
Another similarity to previous works is the availability of the three sandstone bodies (Stray,
Red, and White) within particular areas of the “Clinton Sandstone.” This study found that the three sand bodies are not always present in the subsurface. In fact, most of the data points within
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this thesis (well samples and geophysical logs) only showed either one or two sand bodies
present at that particular area. One of Suphasin’s (1979) arguments was that the “Clinton
Sandstone” was too erratic in the subsurface to map. A main reason for this was the absence of
one or more sandstone bodies within the “Clinton Sandstone.” Suphasin (1979) went on to
explain that the sand bodies missing within the “Clinton Sandstone” were constantly changing
and ultimately unpredictable.
One of the most important similarities between this study and another previous work is the same types of potential reservoirs being found in the “Clinton Sandstone.” Three different reservoirs were described by Keltch (1985) in Guernsey County, Ohio. These three reservoirs
consisted of meander point bars, distributary channel fill, and distributary mouth bars (Keltch,
1985). The meander point bar areas were discontinuous, 4.5 - 7.5 m thick, and represented a
potential quality reservoir (Keltch, 1985). The distributary mouth bar areas varied in size from 9
- 18 m and were the most common type of reservoir. Distributary channel fill areas ranged in size
from 12 - 21 m and represented the best potential reservoir within the “Clinton Sandstone.”
The same three types of deposits have been found in this study. Meander point bars are
somewhat common and generally thin. Distributary mouth bars are the most common type of the
three deposits found within the cores studied. Only one distributary channel deposit was found in
the cores studied but it was the majority of well 2941.
Petroleum Geology
The depositional environment in this study ranges from delta plain, to delta front, to prodelta.
Within these three environments are three known potential types of reservoirs. The delta plain
deposits contain meander point bar areas, which are thinner than the other two potential
reservoirs. Meander point bars typically contain well-graded sands and will show a fining-
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upwards sequence. These meander point bar deposits are more difficult to locate than other
potential reservoirs because they are discontinuous and thin. A meander point bar deposit was
found in well 2866, but according to the Ohio Geological Society (1985) most meander point bar
deposits are found in the “Red Clinton.”
The second type of potential reservoir within the “Clinton Sandstone” is distributary mouth bar deposits. These deposits generally show a coarsening-upwards sequence accompanied by heterolithic sandstone-mudstone bedding. These deposits are typically thicker than meander bar accumulations and represent more of a gradual sand influx (Ohio Geological Society, 1985).
Distributary mouth bars are more common than the other two potential reservoirs but are generally the least promising reservoir when compared to the other two (Ohio Geological
Society, 1985).
The final potential reservoir located in the “Clinton Sandstone” is the distributary channel.
These deposits are typically located in the delta front environment but can also be present in a delta plain environment. Identifying these deposits can be done by looking for blocky log signatures or finding thick, massive sandstone bodies within well samples. These are the thickest of the three potential reservoirs and are also the easiest to find based on their size and simplicity represented in log or physical form. A great example of a distributary channel deposit is well
2941 (Figure 16). The bottom two-thirds of the well contains indistinctly cross-bedded and massive sandstone bodies with very little mudstone interruption.
After evaluating this study area and considering petroleum implications, it is clear that there is potential for finding hydrocarbons within the “Clinton Sandstone.” However, there are a couple factors that must be addressed to ensure the most successful possible outcome.
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This unit as a whole is a tight-gas formation. The grains are generally medium to fine-grained and tightly compacted. The tight nature of the grains significantly decreases not only porosity but also permeability. Another component to this topic is the presence of quartz overgrowths. These overgrowths add to the poor porosity and permeability within the ‘Clinton Sandstone.” A porosity reading was not calculated as part of this thesis but Msek (1973) conducted one in Perry
County and found the porosity to be 8 – 14%.
The other problem with this study area is the strong presence of tidal influences. Every well described in this thesis contained shale partings, and sometimes mud chips and mud drapes.
These features can act as baffles within sandstone units and create fluid barrier flows. The only area of these wells that was generally free of tidal influence was the distributary channel deposit located in well 2941.
Several decades ago, an area like this would have been considered risky based on the information found in this thesis. But with the technological advances and the emergence of horizontal drilling, an area such as this has a better chance of being economically feasible.
Drilling horizontally into this area can potentially avoid several problems 1) meander point bar deposits are discontinuous (Ohio Geological Society, 1985). Horizontal drilling can potentially drill through the divided bodies and connect them. 2) Distributary channel deposits may contain permeability barriers (Ohio Geological Society, 1985). Horizontal drilling compared to vertical drilling has the possibility to break through some permeability barriers and connect the majority of the reservoir. And 3) distributary mouth bars commonly surround distributary channel deposits. If drilling vertically, one would have to drill several times to hit all possible reservoirs. But if horizontal drilling is used, all of the available reservoirs in that given area could hypothetically be drilled through and connected to the borehole with just one drill operation.
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Hydraulic fracturing is another technique that should be used on the “Clinton Sandstone” in this study area. The tight nature of the grains severely hinders fluid flow through the reservoir.
Hydraulically fracturing an area will create many pathways to the borehole and significantly increase production potential. The fracking also has the ability to breakdown internal baffles, caused by mudstone, within a given reservoir.
Future work in this area could include porosity and permeability studies to gain a better insight as to exactly what the conditions are for possible future drilling. Better porosity and permeability in an area will raise the chances of drilling a successful well. Another aspect that may be of interest is creating isolith maps ranging from 50 – 75% clean sand. These isolith maps will show the areas that have more clean sand present. This pertains to the “Clinton Sandstone” because the best known reservoirs are sand bodies that generally do not contain mudstone or have very little.
There were four natural fractures observed in the well samples described for this study. It may be worthwhile for a researcher in the future to look at these natural fractures and any others that they can find, and observe them using Cathodoluminescence. This would give a much closer look at the fractures, identify if the fractures have any minerals precipitating in them, and possible find more fractures that cannot be seen with the naked eye.
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SUMMARY AND CONCLUSIONS
This thesis included lithofacies analysis from six cores, petrofacies analysis from 16 thin sections, and subsurface geophysical log analysis from 15 different wells, to better understand the sedimentology, stratigraphy, subsurface trends, and structure of the “Clinton Sandstone.”
Analysis of the six cores observed show a tidally-influenced delta environment containing five distinct sub environments consisting of meander point bars, interdistributary bays, distributary channels, distributary mouth bars, and prodelta deposits. Previous studies of the “Clinton
Sandstone” have identified the unit ranging from delta plain to prodelta, which is consistent with this thesis, but tidal influence in the “Clinton Sandstone” was previously not a main point of emphasis.
Many sedimentary structures observed in the “Clinton Sandstone” are consistent with a deltaic environment that has experienced tidal influences. These structures present would include wavy bedding, flaser bedding, lenticular bedding, massive bedding, deformational structures, and mudstone intraclasts. Other structures not necessarily associated with tidal influences, but commonly found in a delta environment consist of trough cross-beds, planar-tabular cross-beds, planar lamination, and bioturbation.
The isopach and the 3-D wireframe map display the general thickness of the “Clinton
Sandstone,” as well as the overall structure of the “Clinton Sandstone” in the subsurface. These maps show the “Clinton Sandstone” thinning from the east to the west, which is consistent with
McCormac et al. (1994), who then further states that the “Clinton Sandstone” eventually pinches out in central Ohio. Two anomalies of uncharacteristically thick sandstones, compared to other data points, are present in Hocking County. The average thickness of the “Clinton Sandstone” in the study area is about 6.67 m.
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The structure and trend of the “Clinton Sandstone” in the subsurface is constantly changing based on the northwest-southeast and northeast-southwest litho-correlation profiles. The unit is not only rising and falling, but it does not always contain all three sandstone layers that comprise the “Clinton Sandstone” (Stray, White, and Red Clinton). The evaluation and description of the six cores from the H.R. Collins Laboratory confirms this because not every core contained all three sandstone beds.
As for the reservoir components of the “Clinton Sandstone,” there are several findings that are noteworthy and have the potential to influence how the unit should be drilled into. The tight nature of the grains in the “Clinton Sandstone” has a profound effect on the porosity of the unit.
The percentage of porosity was not calculated as part of this study, but it was evident from the photomicrographs that very little porosity is available. Previous studies from Miller (1982) and
Msek (1973) found the porosity of the “Clinton Sandstone” to be 0 – 13% and 8 – 14%, respectively. Permeability of the “Clinton Sandstone” is also not particularly good as there are quartz overgrowths, mud drapes, and mud baffles throughout the evaluated cores. Four natural fractures were observed in the core samples evaluated, but the overall usefulness of these fractures is very minimal since the fractures only ranged from 4 – 6 cm in length.
Based on the information provided in this thesis, it is recommended that horizontal drilling and fracturing be used when trying to extract gas or oil from the “Clinton Sandstone.” Drilling horizontally, as opposed to vertically, will lower the chances of encountering reservoir compartmentalization issues since it will most likely drill through several secluded reservoirs.
The fracturing technique will improve hydrocarbon recovery by fracturing the existing unit several hundred feet in each direction, thus greatly increasing the permeability of the unit and possibly connecting isolated reservoirs to the borehole.
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APPENDIX A: GEOPHYSICAL LOGS
Figure A-1. Well log for well 2866.
Figure A-2. Well log for well 2941.
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Figure A-3. Well log for well 2943
Figure A-4. Well log for well 2980.
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Figure A-5. Well log for API 34045204650000.
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Figure A-6. Well log for API 34073226160000.
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Figure A-7. Well log for API 34127267800000.
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Figure A-8. Well log for API 34127268100000.
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Figure A-9. Well log for API 34163205850000.
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Figure A-10. Well log for API 34163208730000.
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Figure A-11. Well log for API 34163202540000.
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Figure A-12. Well log for API 34045205000000.
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Figure A-13. Well log for API 34045209720000.
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Figure A-14. Well log for API 34073206350000.
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Figure A-15. Well log for API 34073206120000.
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APPENDIX B: CORE LOGS
Figure B-1. Symbols used to represent sedimentary structures in the well sections.
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Figure B-2. Well log of well 2866.
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Figure B-3. Well log of well 2866.
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Figure B-4. Well log of well 2941.
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Figure B-5. Well log of well 2942.
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Figure B-6. Well log of well 2943.
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Figure B-7. Well log of well 2943.
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Figure B-8. Well log of well 2980.
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Figure B-9. Well log of well 2980.
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Figure B-10. Well log of well 2965.
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Figure B-11. Well log of well 2965.
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Figure B-12. Well log of well 2965.