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Facies Characterization of the Lower () and the Jura- Success Formation of West-central

Dan Kohlruss 1

Information from this publication may be used if credit is given. It is recommended that reference to this publication be made in the following form: Kohlruss, D. (2017): Karst facies characterization of the Lower Carboniferous (Mississippian) Madison Group and the Jura-Cretaceous Success Formation of west-central Saskatchewan; in Summary of Investigations 2017, Volume 1, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2017-4.1, Paper A-2, 11p.

Abstract The Lower Carboniferous (Mississippian) Madison Group and the Jura-Cretaceous Success Formation in the Kindersley– Kerrobert area of west-central Saskatchewan combine to represent a significant karst terrain. The marine Madison were subjected to a long period of exposure, erosion and weathering, which resulted in a substantial amount of structural irregularity at its upper surface, along with abundant decomposition of the limestones both at surface and below. The resulting karst byproduct is the primary environment in which the Success Formation formed within the study area. Analysis of drillcores, drill-cutting samples and geophysical well logs within the study area resulted in the identification of six distinct recurring karst facies, as well as three karst facies associations. The karst facies encountered are 1) grading to matrix-supported -pebble conglomerate; 2) matrix-rich, clast-supported chaotic chert and breccia; 3) crackle breccia; 4) mudstone; 5) chaotic mud and chert rubble breccia/conglomerate; and 6) crackle-mosaic breccia. The karst facies associations represented are 1) collapsed cave; 2) preserved cave roof; and 3) epikarst. The Success Formation in the study area is a known oil producer, represented by three distinct and separate reservoirs. Two of the reservoirs are discussed in this paper, as they are represented by the collapsed cave and epikarst facies associations. Keywords: Success Formation, Madison Group, Mississippian, , Cretaceous, west-central Saskatchewan, karsting, karst facies interpretation, karst-controlled reservoirs, heavy oil

1. Introduction The purpose of this study is to identify and clarify the genetic relationships of key Upper Paleozoic and Mesozoic rocks within the Kindersley–Kerrobert area of west-central Saskatchewan. Specifically, this paper will detail the relationship between the karst facies, and facies associations, of the Lower Carboniferous (Mississippian) Madison Group and the Jura-Cretaceous Success Formation (Figure 1). This clarification will put forward a model for better understanding and predicting the controls on reservoirs described in this study. The Madison Group rocks in the study area are generally termed “Undifferentiated” or as Souris Valley Formation (White, 1969; Christopher, 2003), but for the purposes of this study have been informally broken up into lower and upper units (Figure 1), based primarily on geophysical well logs and core descriptions. The lower unit is composed of alternating and , and the upper unit is represented by calcareous shale transitioning upward gradually to a muddy limestone. The Success Formation in west-central Saskatchewan can be observed as altered carbonate rocks or fluviatile clastic rocks, depending upon its areal distribution and/or stratigraphic position. The Success is distributed on the Kindersley structural terrace and is in disconformity with all subjacent strata, including the overlying

1 Saskatchewan Ministry of the Economy, Saskatchewan Geological Survey, 201 Dewdney Avenue East, Regina, SK S4N 4G3 Although the Saskatchewan Ministry of the Economy has exercised all reasonable care in the compilation, interpretation and production of this product, it is not possible to ensure total accuracy, and all persons who rely on the information contained herein do so at their own risk. The Saskatchewan Ministry of the Economy and the Government of Saskatchewan do not accept liability for any errors, omissions or inaccuracies that may be included in, or derived from, this product.

Saskatchewan Geological Survey 1 Summary of Investigations 2017, Volume 1 (Christopher, 2003; Figure 1). The Success was deposited and/or developed during Late Jurassic time and is a surviving remnant of the pre-Cretaceous erosional phase (Christopher, 2003). Maycock (1967) first described the Success deposits in the Kindersley–Kerrobert area, and White (1969) later described the Success deposits specifically in the northern part of the study area. Christopher (2003) described and characterized the Success Formation in greater detail, and highlighted the various depositional regions of the formation across Saskatchewan, stressing the importance of kaolinite—an abundant component of the Success Formation—when differentiating it from the Mannville Group. In the study area, the Success Formation is primarily formed on or deposited within a paleo-upland, topographic basin where it overlies the Madison Group. The Madison Group was originally dissected by fluvial action and altered by a long period of weathering and decomposition during its post-Mississippian emergence (Maycock, 1967; White, 1969; Christopher, 2003). Sando (1988) placed the time of paleokarst activity on Madison rocks in and from early Meramecian to Morrowan, but it may have lasted even longer in west-central Saskatchewan. The result was an extremely irregular Madison surface and erosional contact between it and the Success Formation or Mannville Group. This study will be the first in a series of reports that will elaborate on this relationship, and the identified facies will later be used to develop detailed, pool-scale structural and isopach maps, along with detailed cross-sections.

Figure 1 – Stratigraphic units discussed in this paper in west-central Saskatchewan’s Kindersley–Kerrobert area (modified from Christopher, 2003). Abbreviations on chart: Fm = Formation, Gp = Group.

2. Study Area and Methods The extent of the study area is bounded on the southeast corner by Township 29, Range 25 west of the Third Meridian (25W3) and on the northwest corner by Township 33, Range 29W3 (Figure 2). The stratigraphy documented in this paper will only include from the base of the Carboniferous Madison Group to the top of the Jura- Cretaceous Success Formation, although for the purposes of future reports the tops and stratigraphy of the Three

Saskatchewan Geological Survey 2 Summary of Investigations 2017, Volume 1 Forks Group through to the top of the Westgate Formation (Figure 1) were picked and recorded. The extent of the study area was chosen based upon known oil production areas within the Success Formation and its equivalents.

Figure 2 – Location of the study area in west-central Saskatchewan. The red stars represent the locations of well cores discussed within the paper and illustrated in core photos; blue polygons represent Success Formation or equivalent oil pools, with their accompanying name in black text; orange polygons represent towns, with their accompanying name in black text. Abbreviations on map: T = Township, R = Range, W = West, Fm = Formation. Abbreviations on inset map: AB = , SASK = Saskatchewan, MAN = Manitoba, MT = Montana, ND = North Dakota.

For the purposes of this study, geophysical well logs were chosen based on the availability of gamma ray (GR) and neutron-density (N-D) logs. Subsequently, nearly 2200 geophysical well logs with GR and N-D traces were analyzed and tops picked, along with the analysis and description of drill-cutting samples and 14 drillcores. Six distinct, recurring karst facies and three facies associations were identified in the Success Formation, based on a combination of lithology, physical rock fabric and/or sedimentary structures. The study of more drillcores would have been desirable, but the nature of the karst facies and the difficulty encountered recovering brecciated rock made the availability of representative core with relatively good quality problematic. Loucks’ (1999) ternary breccia and cave-sediment fill classification system was used as a standardized means to describe the observed rock fabrics within the study area.

Saskatchewan Geological Survey 3 Summary of Investigations 2017, Volume 1 3. Karst Facies Descriptions and Interpretation The six karst facies identified in this study are described below, and their main characteristics are summarized in Table 1.

Table 1 – Summary of karst facies identified within the study area.

KARST FACIES OCCURRENCE/ DESCRIPTION RESERVOIR QUALITY INTERPRETATION CONTACT Facies 1: Between Facies 2 and Light grey to green Poor reservoir due to poor Cave floor sediment fill. Mudstone grading to matrix- Madison Group. Contact with mudstone grading upward sorting and low-permeability supported chert-pebble Madison is erosional and into well-rounded, mud- mud matrix. Chert fragments conglomerate grades into Facies 2. matrix–supported chert- locally have earthy texture, pebble conglomerate. stained by oil. Facies 2: Can occur either above, Predominantly white angular Good reservoir due to Cave roof and wall collapse, Matrix-rich, clast-supported below or perched within the chert fragments ranging from permeability of sandstone including cave sediment fill. chaotic chert and sandstone Upper Madison; commonly millimetre to centimetre and high mechanically breccia found below Facies 3 and scale within a fine-grained fractured chert breccia most commonly perched sandstone matrix. fragments. This facies is within the Upper Madison. usually stained with heavy oil. Facies 3: Above Facies 2; usually Fractured light grey to pink Poor reservoir due to clay- Disturbed cave roof. Also Crackle breccia within the Upper Madison clogged fractures and very represents a zone of Group carbonates. (crinoidal). Fractures low permeability/porosity percolation of meteoric commonly are sites of limestone. No oil staining. waters filtering from the replacement “haloes”, surface epikarst zone altering limestone to clay. downward through the vadose zone toward the phreatic water table. Facies 4: Observed at top of the Red to yellow mudstone. Non-reservoir facies. Red clay produced from Mudstone Madison Group, below or weathering of limestone within Facies 4, or between (terra rossa) under oxidizing the contact of the Madison conditions in the vadose Group and Facies 2. zone. The clays were likely transported from surface into the cave. Facies 5: Above Facies 2 or 3; usually White to grey chert breccia Fair reservoir due to Epikarst zone. Surface area Chaotic mud and chert a gradational contact but can mixed with green-grey abundant fracture exposed to extreme and rubble breccia/conglomerate be a sharp erosional contact. mudstone matrix. Chert permeability and porosity, prolonged weathering and fragments are generally although common green degradation resulting in centimetre scale and well- clays likely clog and impede dissolution and rounded, usually with an oil flow. Commonly heavy-oil decomposition of the internal crackle breccia stained. Madison Group carbonate texture. Ranges from mud- rocks. Meteoric water matrix–supported to clast- penetrates through joints and supported. fractures, rounding irregular blocks into rubble. Rare paleosol preserved at top, with massive siltstone grading upward into coal. Facies 6: Commonly stratigraphically Interbedded sandstone and Good reservoir facies due to Disturbed cave roof caused Crackle-mosaic breccia above Facies 4. white mudstone. Some the high permeability and by collapse of karst at depth. original sedimentary porosity of the . Collapse occurred after structures such as cross- Regularly stained with heavy burial, as a result of loading bedding preserved but oil and locally has a natural and compaction. primarily massive. Angular gas cap. brecciation and evidence of collapse.

a) Facies 1: Mudstone Grading to Matrix-supported Chert-Pebble Conglomerate Facies 1 (F1) is a light grey to green mudstone that grades upward into a mud-matrix–supported chert-pebble to very rarely chert-cobble conglomerate (Figure 3A). Chert pebbles range from light grey to white and exhibit earthy to glassy texture. Where the chert pebbles have an earthy texture, they can be heavily oil stained. This facies has been

Saskatchewan Geological Survey 4 Summary of Investigations 2017, Volume 1 observed in erosional contact above the limestones of the upper unit of the Madison. F1 has been observed below, and grades into, the overlying Facies 2 (F2; Figures 3A and 4). This facies exhibits poor sorting and subsequent low permeability due to the mud matrix, but the earthy-textured chert fragments are commonly oil stained. F1 is interpreted to have poor reservoir potential. The textures and rounding of the chert pebbles indicate they were transported a significant distance before deposition. The mud portion was likely deposited as a result of either suspension fall-out in a low-energy environment or as mass flow of saturated muddy sediment. The rounded pebbles could have been transported as bed load or part of a mass flow. The poorly sorted nature indicates mass movement of the muds, pebbles and cobbles together, and deposition contemporaneously. This facies is interpreted to have formed as cave sediment fill deposited along a cave floor.

b) Facies 2: Matrix-rich, Clast-supported Chaotic Chert and Sandstone Breccia Facies 2 (F2) is composed predominantly of white, angular chert fragments ranging in size from millimetre to centimetre scale. The texture of the chert ranges from glassy to earthy. The brecciated fragments are clast supported and the matrix is composed of predominantly fine-grained quartz (chert?) sandstone with a minor component of light grey-green mud. The breccia clasts are organized very chaotically, with no evidence of original layering or orientation (Figure 3B). This facies can be observed directly overlying, below or perched within the upper unit of the Madison, or overlying Facies 1 or below Facies 3. The earthy-textured chert fragments and sandstone component of the matrix are commonly oil stained (Figure 3B). The sandstone and earthy-textured chert exhibit good porosity and together they represent good reservoir potential for this facies. The chert is presumed to be a result of diagenetic alteration of the host rock, either from phreatic waters, percolating vadose-zone waters or formation waters, but the source of the silica for silicification, and its timing, is not apparent at this time. F2 is highly brecciated and chaotic, with very little evidence of transport beyond gravitational, indicating the facies formed as a result of collapse. This facies’ stratigraphic relationship to the Madison Group (regularly observed perched within the upper unit of the Madison) and its sedimentary structures are indicative of a cave-roof and -wall karst-collapse environment.

c) Facies 3: Crackle Breccia Facies 3 (F3) is represented by highly fractured light grey to pink fossiliferous () limestone of the upper unit of the Madison (Figure 3C). The fractures appear as very fine discrete cracks or as robust muddy altered zones surrounding limestone clints (Figure 3C). Varying degrees of alteration have been observed, but the fossil material is not affected by the alteration process that affected the original limestone bedrock; well-preserved fossil material is visible within the muddy altered zones and the unaltered limestone. The crinoids are observed to be along sedimentary planes and offer an indication of bedding. Though brecciated, the original rock is still very organized, and the original bedding of the limestone is relatively undisturbed. No evidence of significant transport distance was observed. F3 has been observed in the upper unit of the Madison, where the upper unit carbonates are preserved above F2. No visible oil staining has been observed within this facies and therefore, for the purposes of this paper, it is considered a non-reservoir facies. F3 represents moderately disturbed, preserved cave roof. The variable development of fractures and subsequent crackle breccia formed as a result of down-warping due to the collapse of paleokarst below. The fractures consequently became a region within the vadose (air-filled) zone where meteoric waters could percolate downward to the phreatic (water-filled) zone. The percolating waters were responsible for the eventual muddy alteration haloes observed around many of the fractures.

Saskatchewan Geological Survey 5 Summary of Investigations 2017, Volume 1

Saskatchewan Geological Survey 6 Summary of Investigations 2017, Volume 1 Figure 3 (previous page) – A) Mudstone grading to matrix-supported chert-pebble conglomerate (Facies 1) composed of light grey to green mudstone grading upward into well-rounded, mudstone-supported chert-pebble conglomerate; this facies is poorly sorted, with low reservoir potential; well 111/09-04-030-28W3, at 805.7 m depth. B) Matrix-rich, clast-supported chaotic chert and sandstone breccia (Facies 2) composed of predominantly white angular chert fragments ranging from millimetre to centimetre scale within a fine-grained sandstone matrix; this facies exhibits good reservoir potential and is a known oil producer in the study area; well 111/09-04-030-28W3, at 802.5 m depth. C) Crackle breccia (Facies 3) composed of fractured light grey to pink fossiliferous limestone (crinoidal); the fractures commonly are sites of replacement “haloes”, altering limestone to clay; well 101/08-12-030-28W3, at 820.9 m depth. D) Mudstone (Facies 4) composed of red to yellow waxy mudstone; well 111/09-22-031- 27W3, at 820.9 m depth. E) Chaotic rubble breccia (Facies 5) composed of white to grey chert breccia mixed with a green-grey mudstone matrix; chert fragments are generally centimetre scale and well rounded, commonly with an internal crackle-breccia texture. This facies ranges from mud-matrix–supported to clast-supported; well 111/15-08-030-26W3, at 854.0 m depth. F) Crackle-mosaic breccia (Facies 6) composed of interbedded sandstone and white earthy mudstone; well 111/15-08-030- 26W3, at 830.8 m depth.

d) Facies 4: Mudstone Facies 4 (F4) is an earthy to waxy mudstone ranging in colour from a rusty red to yellow (Figure 3D). This facies has been observed at the top of the Madison Group where in contact with F2, and below or within F5. F4 have no visible oil staining, so for the purposes of this paper are considered a non-reservoir facies. F4 is interpreted to have formed as a result of the weathering of limestone under oxidizing conditions in the vadose zone, and is commonly referred to as terra rossa. Where found at the top of the Madison Group, it likely formed in situ as a soil, but where observed stratigraphically within F2 or F5 the muds were likely mobilized at surface and deposited as a sediment flow within the karst voids.

e) Facies 5: Chaotic Mud and Chert Rubble Breccia/Conglomerate Facies 5 (F5) is a mix of light grey to white, earthy, porous chert in a matrix of light grey to green-grey mudstone with minor sandstone. The facies is very crumbly and rubbly with predominantly rounded to subangular millimetre- to centimetre-scale breccia clasts (Figure 3E). Large massive chert clasts exhibit internal crackle brecciation. Breccia ranges from mud-matrix–supported to clast-supported. This facies exhibits fair reservoir potential due to the porosity of the earthy chert and the abundant fractures. The common green and grey mudstone mixed with the breccia likely reduces porosity and impedes oil flow. Where porosity is present the facies is generally stained with heavy oil. F5 occurs gradationally above F2 or F3 and has been observed capped by paleosols of the Mannville Group (Figure 4). This facies is indicative of an epikarst zone located just below the soil horizon. This is an area of enhanced dissolution in the uppermost zone of the Madison Group bedrock. This zone would also be affected by mechanical weathering along with chemical weathering associated with dissolution. The mechanical and chemical weathering is responsible for the rubbly, “rotten” texture that is observed in this facies.

f) Facies 6: Crackle-Mosaic Breccia Facies 6 (F6) is an interbedded quartz sandstone and white mudstone. Original sedimentary structures, such as cross-bedding, are preserved locally, but the original rock is primarily massive. Most notably, the interbedded quartz sandstone and white mudstone are overprinted by a crackle-mosaic breccia to rarely chaotic breccia texture (Figure 3F). The breccia fragments are mostly angular, with a minor component being subangular to subrounded. Centimetre-scale white mudstone beds are generally tilted and disrupted as well. F6 is most commonly observed stratigraphically above Facies 5, but has also been observed in sharp erosional contact with F3 and F4.

Saskatchewan Geological Survey 7 Summary of Investigations 2017, Volume 1 This facies represents good reservoir rock due to the relatively high permeability and porosity of the sandstone. The sandstone is regularly stained with heavy oil, and a natural gas cap has been observed in some geophysical well logs. F6 is interpreted to be part of a fluvial depositional system that was disrupted postdepositionally by the collapse of paleokarsts (caverns) at greater depth, resulting in a brecciated overprint of the original sedimentary structures. Because this facies originated as part of a fluvial depositional system and was not crucial to the paleokarst model, the author chose to omit it from Figure 4. Although not crucial to the paleokarst model, the crackle-mosaic breccia facies is important evidence for vertical movement at depth, supporting the interpretation of postdepositional cavern collapse.

4. Karst Facies Associations and Origins

a) Facies Association 1: Collapsed Cave The collapsed cave facies association 1 (FA1) comprises F1 and F2, as observed in vertical profile within the study area. The lowest portion comprises F1 and represents cave sediment fill along the paleo-cave floor. This is followed by the matrix-rich, clast-supported chaotic angular chert and sandstone breccia of F2 (Figure 4). The vertical stacking relationship observed in FA1 is typical of a collapsed paleo-cave. F1 sedimentation likely occurred during the vadose zone phase of the cave’s history, and represents sediment that would have been transported through fluvial-like processes along the cave floor, but which originated from outside the cave system and was transported into the cave by surface runoff (Loucks and Mescher, 2001). F2 sediments are a result of collapse of the cave wall and ceiling. This facies also likely formed in the vadose zone phase and during burial and loading caused by younger sediments. The facies association is a result of dissolution causing cavern collapse and fill, where the majority of the clasts are derived from the ceiling and wall collapse and the finer material was deposited through water transport (Loucks and Mescher, 2001).

b) Facies Association 2: Preserved Cave Roof The preserved-cave-roof facies association 2 (FA2) is composed solely of F3 and is observed within the upper unit of the Madison Group. This facies association is not found everywhere but, where present, it sits stratigraphically above FA1 (Figure 4). This facies association is interpreted as disturbed but relatively intact host rock or, in this case, cave roof. This relatively intact nature is fairly continuous but is offset locally by small centimetre-scale faults and is overprinted with crackle breccia. The breccia network exhibits varying degrees of weathering and alteration to clay, depending upon the proximity to facies association 3 (FA3). Increased alteration is observed the closer the proximity to FA3. The crackle breccia is a result of downwarping caused by the collapse of deeper passages in the cave.

c) Facies Association 3: Epikarst The epikarst facies association 3 (FA3) is composed of F4 and F5, as observed in vertical profile. The stacking relationship can be with either F4 or F5 at the lowest levels, but these facies can be found in any relative position within the facies association; F4 can even be found perched within F5 (Figure 4). The facies association relationship of F4 and F5 is typical of an epikarst environment. This is the surficial karst expression represented by irregular pits, etched surfaces and dissolution channels that are concentrated within the upper few metres of rock (Mylroie and Carew, 1995), in particular in weathered limestone terrains. Mylroie and Carew (1995) also noted that the epikarst environment is very laterally extensive; this also holds true in the study area. This lateral continuity was also recognized in work by Maycock (1967), White (1969) and Christopher (1974, 2003). The red colouration of the clays is typical of oxidation of limestones into clays and is recognized as a terra rossa horizon. Where the red muds are found perched within F5 they were transported from surface and were deposited within voids in the epikarst environment. It is presumed the epikarst environment is quite mature and was subjected

Saskatchewan Geological Survey 8 Summary of Investigations 2017, Volume 1 to prolonged weathering and karst processes, as evidenced by the extreme rubbly nature of the rocks in this facies association. This was likely enhanced by collapse of caverns below, adding to the fractured nature of the rock, and creating further fractures and subsequent surface area for meteoric waters to percolate through, alter and dissolve. In the core from well 141/06-23-31-23W3 (Lic# 85H152; not shown on Figure 2), a paleosol topped by a coal layer is observed directly on top of FA3. This sequence has also been observed in many well logs throughout the study area but, unfortunately, there were no cores in the mapped study area intersecting the paleosol facies. Through necessity, cores from outside of the mapped area were also logged, including core 141/06-23-31-23W3, to better understand facies that were solely observed in well logs from the mapped area. Paleosols are often coincident with karst development, and the underlying epikarst can be completely covered (Mylroie and Carew, 1995).

Figure 4 – Schematic litholog illustrating the various facies and facies associations (FA) identified in the study area, and the idealized stacking pattern.

Saskatchewan Geological Survey 9 Summary of Investigations 2017, Volume 1 5. Discussion Recognition of karst facies and their stacking relationships is the first step in developing an accurate predictive model for the various karst reservoirs in the Kindersley–Kerrobert area. Though karst features in west-central Saskatchewan’s Madison Group and Success Formation have been described before by Maycock (1967), White (1969) and Christopher (2003), this study is the first to attempt identification of the various reservoirs and individual paleokarst environments in the Kindersley–Kerrobert area. To further support the observations reported in this study, it may be noted that Madison paleokarst features have been recognized in other areas of North America, in particular by Sando (1988). He recognized evidence of karsting within the Madison outcrops of southeastern Wyoming and southern Montana, where he described not only an upper solution zone (Bull Ridge Member), but also a lower solution zone (Little Tongue Member) as part of the paleokarst system. This is consistent with the observations in the Kindersley–Kerrobert area, and Sando’s upper and lower solution zones are likely equivalent to this study’s FA3 and FA1, respectively. Sando (1988) also observed many other karst features in outcrop that have been observed in drillcore in west-central Saskatchewan. For example, he observed variable relief and thickness of the upper solution zone (FA3-equivalent) where he similarly observed red and green . He also observed abundant chert breccia directly overlying Madison-derived collapsed roof rock, again, much like FA3 (Figure 4). Sando (1988) also observed enlarged joints at the top of the Madison that would be equivalent to the upper portions of FA2’s altered and crackle-brecciated limestones. Finally, he also observed caves filled by collapsed angular chert roof- and wall-rock (FA1-equivalent; Figure 4). The observations in west-central Saskatchewan are therefore consistent with those for other areas in North America where the Madison Group is present, and are also consistent with other karst systems (modern) and paleo- cave (ancient) classifications (Esteban and Klappa, 1983; Esteban and Wilson, 1993; Loucks, 1999). A carbonate subaerial exposure surface represents a solely diagenetic environment rather than a depositional one. Once there are subaerial conditions, stabilization and non-deposition of sediment, and sufficient time available for subaerial diagenetic processes to affect the exposed rock and cause alteration, a karst terrain will develop (Esteban and Klappa, 1983). This is also true of the Kindersley–Kerrobert area during the post-Mississippian to pre- Cretaceous time, when the Madison Group became exposed and was originally altered by a long period of weathering and decomposition (Maycock, 1967; White, 1969; Christopher, 2003). The karst characterization in this study has also led to the identification of three separate and distinct reservoirs in the Kindersley–Kerrobert area’s Success Formation. Two karst reservoir facies can be identified: the collapsed cave reservoir, and the epikarst reservoir. As well, a disrupted fluvial reservoir (F6) was also identified in this study, but as it is not specifically related to the karst terrain it will not be discussed as part of this paper. Loucks (1999) pointed out that many of the features associated with paleokarst—such as cavernous porosity, inter- breccia porosity, fracture porosity in clasts, roof or walls, and matrix porosity in cave sediment—can all be excellent oil reservoirs. Loucks (ibid) also noted that collapsed paleo-caves can also be an excellent reservoir, much like that recognized as FA1 in the Kindersley–Kerrobert area. The FA3, epikarst reservoir, is a result of inter-breccia porosity development along with the earthy texture of the chert and intergranular porosity of the sand matrix, another example of a paleokarst reservoir. In past Saskatchewan government reports (e.g., White, 1969; Christopher, 2003), FA1 and FA3 were not differentiated. Separating the collapsed cave system (FA1) from the epikarst system (FA3), as has been accomplished in this study, is especially valuable because of the economic significance of the two facies associations/reservoirs and their significant heavy oil content. The heterogeneous nature of karst terrains, abundant trapping opportunities (due to the heterogeneous nature of paleokarst systems), and their propensity for compartmentalization make them attractive, but complex and unpredictable targets. Kerans (1988) and Loucks (1999) recognized paleokarst environments as valuable reservoirs but noted they are often difficult to identify and recommended the use of 3-D seismic, cores, geophysical well logs and borehole imaging, where available, to help find and identify paleokarst reservoirs.

Saskatchewan Geological Survey 10 Summary of Investigations 2017, Volume 1 This study is the first step in furthering the understanding of the karst terrain observed in the Kindersley–Kerrobert area. The conclusions presented here will eventually lead to further petroleum development and identification of future exploration targets.

6. Future Work With the identification of three distinct karst reservoirs, along with associated non-reservoir karst facies, future work will include mapping the study area through the use of structure, isopach, production and oil-cut contour maps, along with detailed, pool-scale cross-sections. It is also planned to develop a predictive model to determine the controls on oil trapping and potentially identify new areas of prospectivity. As the study area was chosen based upon known Success Formation oil production, future work will entail expanding the study area to include areas yet to have production from the Success Formation, further aiding the identification of prospective areas.

7. Acknowledgments The author would like to thank Rae McClintock for her very valuable work locating drillcores, reviewing drill-cutting samples and picking major formational tops for this study. The author would also like to thank the staff at the Saskatchewan Geological Survey’s Petroleum Geology Unit for their valuable input and discussions for this paper.

8. References Christopher, J.E. (1974): The Upper Jurassic Vanguard and Lower Cretaceous Mannville Group of Southwestern Saskatchewan; Saskatchewan Department of Mineral Resources, Report 151, 349p. Christopher, J.E. (2003): Jura-Cretaceous Success Formation and Lower Cretaceous Mannville Group of Saskatchewan; Saskatchewan Industry and Resources, Report 223, CD-ROM. Esteban, M. and Klappa, C.F. (1983): Subaerial exposure environment; Chapter 1 in Carbonate Depositional Environments, Scholle, P.A., Bebout, D.G. and Moore, C.H. (eds.), American Association of Petroleum Geologists, Memoir 33, p.1-54. Esteban, M. and Wilson, J.L. (1993): Introduction to karst systems and paleokarst reservoirs; in Paleokarst Related Hydrocarbon Reservoirs, Fritz, R.D., Wilson, J.L. and Yurewicz, D.A. (eds.), Society for Sedimentary Geology (SEPM), Core Workshop No. 18, p.1-9. Kerans, C. (1988): Karst-controlled reservoir heterogeneity in Ellenburger Group carbonates of west Texas; AAPG Bulletin, v.72, p.1160-1183. Loucks, R.G. (1999): Paleocave carbonate reservoirs: origins, burial-depth modifications, spatial complexity, and reservoir implications; AAPG Bulletin, v.83, p.1795-1834. Loucks, R.G. and Mescher, P.K. (2001): Paleocave facies classification and associated pore types; in A Geologic Odyssey: AAPG Southwest Section Annual Meeting, Dallas, Texas, March 11 to 13, papers and abstracts on CD-ROM, 18p. Maycock, I.D. (1967): Mannville Group and Associated Lower Cretaceous Rocks in Southwestern Saskatchewan; Saskatchewan Department of Mineral Resources, Report 96, 108p. Mylroie, J.E. and Carew, J.L. (1995): Karst development on carbonate islands; Chapter 3 in Unconformities and Porosity in Carbonate Strata, Budd, D.A., Saller, A.H. and Harris, P.M. (eds.), American Association of Petroleum Geologists, Memoir 63, p.55-76. Sando, W.J. (1988): Madison Limestone (Mississippian) paleokarst: a geologic synthesis; in Paleokarst, James, N.P. and Choquette, P.W. (eds.), Springer, New York, NY, p.256-277. White, W.I. (1969): Geology and Petroleum Accumulations of the North Hoosier Area, West-central Saskatchewan; Saskatchewan Department of Mineral Resources, Report 133, 37p.

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