The Niobrara and Carlile Formations of Western Saskatchewan – Preliminary Investigations
M. Yurkowski, A. Marsh, and K. Heinneman
Yurkowski, M., Marsh, A., and Heinneman, K. (2006): The Niobrara and Carlile formations of western Saskatchewan – preliminary investigations; in Summary of Investigations 2006, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2006-4.1, CD-ROM, Paper A-14, 8p.
Abstract Mapping of the Upper Cretaceous (Turonian to Santonian) Carlile and Niobrara formations has recently been initiated to improve our understanding of their stratigraphic architecture. Four preliminary regional cross sections of the two formations in southwestern Saskatchewan were created, and the only Carlile core in the study area was examined. Initial investigations indicate that the Niobrara is truncated in a northeasterly direction by the Milk River Formation. The middle Niobrara Medicine Hat Member, also, appears to thin to the northeast independently of the sub–Milk River contact. The Carlile Formation also thins, but in a more northerly direction. Keywords: Upper Colorado, Turonian, Santonian, Carlile Formation, Niobrara Formation, First White Specks, Medicine Hat Member, Govenlock, southwestern Saskatchewan.
1. Introduction Southwestern Saskatchewan has a long history of natural gas production from the Niobrara Formation, particularly from the middle member, the sandy Medicine Hat. Some production is now also being reported from the Carlile Formation in the Monchy Pool, where it is commingled with production from the Belle Fourche Formation (a unit that is also informally known as Second White Speckled Sandstone (2WS)).
Understanding the geometry of the Niobrara and Carlile formations, their sedimentology, and their stratigraphic relationships with the overlying Montana Group Milk River Formation and underlying Colorado Group Second White Specks Formation is important in determining the controls on gas distribution within them. Consequently, mapping of the Carlile and the Niobrara has recently been initiated. This paper presents geophysical log cross sections of the Niobrara and Carlile of southwestern Saskatchewan linking the reference sections of Gilboy (1993, 1996) and Nielsen (2003) to current studies in the central and eastern part of the province (Christopher et al., this volume).
The study area (Figure 1) lies between Rges 27W3 and 27W2 and Tps 5 to 21. Three west-east cross sections are situated approximately along Tps 5 (A-A', Figure 2), 11 (B-B', Figure 3), and 21 (C-C', Figure 4). They are tied into Gilboy’s (1996) north-south cross section along Rge 27W3M. The north-south cross section D-D' (Figure 5) along Rge 6W3 parallels Gilboy’s (1996) section. Stratigraphic tops for the Milk River, Upper Colorado (Niobrara), Medicine Hat, and the Second White Specks were, for the most part, taken from Marsh and Heinneman (2005); those for the Govenlock and Carlile were based on Gilboy’s (1996) cross section. A paucity of core outside the primary Medicine Hat producing areas precludes utilizing core to aid in the log interpretation.
2. Niobrara Formation The Niobrara Formation of southwestern Saskatchewan can be subdivided into: 1) an upper member comprising chalky calcareous shale (First White Specks Member (1WS)); 2) a middle gas-prone member that coarsens upward and consists of muddy, very fine- to fine-grained siltstone and sandstone (Medicine Hat Member); and 3) a lower shale unit containing numerous bentonite beds that Gilboy (1996) informally referred to as the Govenlock member. Nielsen et al. (2003) formally defined the Niobrara Formation in Saskatchewan, adopting the earlier terminology for the upper members but defining a lower unit, the Verger Member, which Pedersen (2004) correlated to the lower sub-unit and the lower part of the middle sub-unit of the Govenlock. Correlation of Gilboy’s (1996) Govenlock through to Texaco Edgell 11/01-04-10-22W3, where Nielsen (2003) identified the Verger/Medicine Hat contact at 979.1 m, shows that at this point the Govenlock and the Verger become essentially the same stratigraphic interval.
Saskatchewan Geological Survey 1 Summary of Investigations 2006, Volume 1
N
Prince Albert
Saskatoon
25
C23 24 27 D’ 21 20 28 31 32 33 25 26 29 30 C’ 42 Moose Jaw Regina 40 41 15 39 Swift Current 38 17 18 19 B12 14 15 37 22 10 13 16 21 36 20 B’ 35 1 2 3 4 34 5 A 5 6 7 8 10 11 9 A’ 1 D 25 20 15 10 5 1 25 W3 l W2 0 50 100 150
Scale in kilometres Figure 1 - Map of Saskatchewan showing locations of stratigraphic cross-sections A-A', B-B', C-C', and D-D'.
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A A’ (D) 1 2 3 4 5 6 7 8 9 10 11
131/14-14-005-27W3/00 141/06-10-005-24W3/00 121/02-18-005-22W3/00 121/10-10-005-20W3/00 111/12-20-005-17W3/00 141/09-01-005-13W3/00 131/01-22-005-1 1W3/00 141/02-07-005-08W3/00 121/06-05-006-06W3/00 121/12-14-005-02W3/00 101/07-13-005-30W2/00 CUBE BA Y SHORE ASCOT ONYX COLGAS BR ET AL PINNACLE EASTBROOK CHEVRON WHITE CREEK HOME SCURR Y HOME SCURR Y INT. HELIUM MANKOT A EOG MCCORD 6-5-6-6 SOCONY SOHIO ELM HB MONT AGUE CYPRESS L 14-14-5-27 ROBSAR T 6-10-5-24 EASTEND 2-18-5-22 10-10-5-20 12-20-5-17 HILLANDALE 9-1-5-13 BRONCHO 1-22-5-1 1 2-7-5-8 KB +749.3 SPRINGS 12-14 7-13-5-30 KB +959.0 KB +972.5 KB +1044.5 KB +972.5 KB +891.4 KB +840.8 KB +956.8 KB +831.8 KB +847.3 KB +858.3 Sp G G Rt G Rt G Rt Rt Rt G Rt Rt G Rt G Rt G Rt G Rt Lea Park 500 600 500 600
700 600 600 Lea Park 500 500
700 700 600 700 600 700 800 Montana 700 Milk River 700 600 600 800 Milk River 800 1WS 700 800 700 800 t 900 Ha 800 800 Medicine Niobrara 700 700 900 900 ? Niobrara Govenlock 800 800 900 900 1000 Carlile Upper Colorado 900 Carlile 900 2WS 2WS 800 800
Gilboy (1996) well 1000
Figure 2 - Geophysical log stratigraphic cross-section A-A' showing relationships of the Carlile, Niobrara, Milk River, and Lea Park formations. Units in metres; 1WS, First White Specks; 2WS, Second White Specks.
B (D) B’ 12 13 14 15 16 17 18 19 20 21 22
101/15-12-010-27W3 131/1 1-33-010-24W3 111/01-04-010-22W3 141/01-16-01 1-17W3 131/13-23-012-15W3 141/09-20-012-13W3 141/07-04-012-09W3 121/06-02-012-08W3 101/07-12-01 1-05W3 131/10-35-01 1-03W3 101/13-27-01 1-28W2 AMUREX ALBERCAN OAK ET AL MAPLE TEXACO EDGELL RENAISSANCE PRIME ET AL LAC RENAISSANCE BRADY VANGUARD BRCL HODGEVILLE DORCHESTER SPC P ALMER SOCONY SOHIO MCCLOUD NO 1 15 CREEK 1 1 33 10 24 1-4-10-22 SIMMIE W 1-16-1 1-17 PELLETIER 13-23-12-15 WYMARK 9-20-12-13 7-4-12-9 6-2-12-8 GRAVELBOURG7-12-1 1-5 10 35 1 1 3 MOSSBANK NO 1 KB +890.6 KB +889.2 KB +1083.7 KB +883.5 KB +882.8 KB +906.5 KB +772.8 KB +726.3 KB +705.9 KB +750.1 KB +687.6 G Rt G Rt G Rt G Rt G Rt G Rt SP Rt G Rt SP Rt 500 Lea Park
500 500 600 600 500 500 500 Lea Park 800 Montana 600 700 600
Milk River 600 600 700 700 600 600 600 1WS
900 700 800 Hat 700
Milk River Medicine
Niobrara 700 ck 800 700 800 700 lo 700 Goven- ? 700 Niobrara 1000 800 900 800 Carlile Carlile Upper Colorado
2WS 800 900 900 2WS 900 800 800
800 100 1 Gilboy (1996) well Nielson (2003) well
Figure 3 - Geophysical log stratigraphic cross-section B-B' showing relationships of the Carlile, Niobrara, Milk River, and Lea Park formations. Units in metres; 1WS, First White Specks; 2WS, Second White Specks.
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C C’ (D’) 23 24 25 26 27 28 29 30 31 32 33 101/07-30-21-27W3/00 141/06-21-21-25W3/00 101/02-03-21-24W3/00 101/04-17-21-23W3/00 141/08-05-22-21W3/00 101/9-19-20-16W3/00 101/16-35-19-10W3/00 101/13-28-19-07W3/00 101/10-33-020-05W3/00 101/03-18-20-01W3/00 101/02-29-21-27W2/00 BAYSEL ET AL MENDHAM EOG LIEBENTHAL CDR S SCEPTRE RIO PRADO LEMSFORD PROFICO ABBEY NOR TH SOCONY MOBIL CABRI SOCONY MOBILARD CDR CAL DERBANK BANKENO ET AL CDR ESKBANK CEGO FINDLA TER 7-30-21-27 6-21-21-25 2-3-21-24 4-17-21-23 8-5-22-21 9-19-20-16 KENNETH 16-35-19-10 13-28-19-7 THUNDER CK 10-33-20-5 3-18-20-1 2-29-21-27 KB +713.2 KB +708.7 KB +705.0 KB +700.7 KB +684.3 KB +667.5 KB +720.5 KB +741.6 KB +656.7 KB +613.6 KB +600.8
Sp Rt G Rt G Rt Sp Rt G Rt G Rt G Rt G Rt G Rt G Rt Sp Rt 400 200
500 300 300 300 300
300 500 300 Lea Park 500
500 300 600 400 Lea Park 400 400 400 400 Montana 600 400 600 Milk River
600 400 700
1WS 500 500 500 500
500 cine Hat Medi- 700 500
? Milk River
Goven- 700 Niobrara lock Niobrara 700 Upper 500
Colorado 800 600
Carlile Carlile 600 600 600
600 2WS
800 600 2WS 800
Gilboy (1996) well 800
Figure 4 - Geophysical log stratigraphic cross-section C-C' showing relationships of the Carlile, Niobrara, Milk River, and Lea Park formations. Units in metres; 1WS, First White Specks; 2WS, Second White Specks.
D (A) (B) (C) D’
9 34 35 36 20 37 38 39 40 41 42 31 121/06-05-006-06W3/00 141/10-30-007-06W3 101/07-09-009-06W3/00 101/08-21-010-06W3/00 101/07-12-01 1-05W3/00 101/11-06-012-05W3/00 101/06-13-014-06W3/00 101/12-22-016-06W3/00 101/09-20-017-06W3/00 101/04-16-018-06W3/00 101/04-33-018-06W3/00 101/10-33-020-05W3/00 EOG MCCORD 6-5-6-6 EOG MEYRONNE 10-30-7-6 A ROYER NO 7-9-9-6 UOHL ARBUTHNOT 8-21-10-6 DORCHESTER SPC GRA VELBOURG DORCHESTER SOCONY MOBIL HB TW CHAPLIN L 9-20-17-6 H B TIDE W ATER CHAPLIN H B TIDE W ATER CHAPLIN BANKENO ET AL THUNDER KB +749.3 KB +751.7 KB +753.5 KB +765.4 GRAVELBOURG 7-12-1 1-5 11-6-12-5W3 SHAMROCK 6-13-14-6 DROXFORD 12-22-16-6 KB +675.1 LAKE NO 2 LAKE NO 3 CK 10-33-20-5 KB +705.9 KB +722.4 KB +736.1 KB +690.4 KB +736.4 KB +746.8 KB +656.7 G Rt G Rt G Rt G Rt G Rt Sp Rt G Rt G Rt G Rt G Rt Sp Rt G Rt 400
400 400 400 400 400 400 500 500 500 500 500 500 500 Lea Park Lea Park 500 500 500 500 500 600 600 600 600 600
600 600 Montana 600 600 600 600 Milk River 600
700 700 700 700 700 Milk River 700 700
Nio- 700 700 700 700 brara 700
800 Niobrara
800 800 800 Upper Colorado 800 Carlile Carlile 800 2WS 2WS 800 800
800 2WS 800 800
800 Figure 5 - Geophysical log stratigraphic cross-section D-D' showing relationships of the Carlile, Niobrara, Milk River, and Lea Park formations. Units in metres; 2WS, Second White Specks.
Saskatchewan Geological Survey 4 Summary of Investigations 2006, Volume 1 The First White Specks Member is differentiated on geophysical logs from the overlying Milk River Formation and from the underlying Medicine Hat Member on geophysical logs by an increase in gamma count and a corresponding decrease in resistivity. These sediments are dark grey calcareous mudstones with numerous calcareous white specks, most likely coccoliths and comminuted shell fragments. Inoceramus and fish scales are abundant. The First White Specks Member is generally very finely laminated and nonbioturbated and has intervals where the rock takes on a flaky appearance. Pedersen (2004) noted that in southwesternmost Saskatchewan silty beds are present. The silty member was not evident on geophysical well logs within the study area; its absence is most likely due to the large distance from the Sweetgrass Arch, which has been perceived to have been the sediment source for the Niobrara (Neilson and Schröder-Adams, 1999). The contact between the overlying Milk River and First White Specks is not cored in the study area and so their exact relationship is unknown. The Medicine Hat Member is the major gas-producing interval within the Niobrara and has been the focus of several previous studies (Hancock and Glass, 1968; Kendall and Simpson, 1974; Simpson, 1981a, 1981b; Gilboy, 1989; Nielsen, 2003; Nielsen et al., 2003). Numerous cores of the Medicine Hat exist and most display three coarsening-upward sequences of fine-grained sandstones intercalated with mudstones (Simpson, 1981b). Bioturbation is extensive, and Neilson et al. (2003) report several chert-pebble surfaces within the Medicine Hat Member of Alberta and Saskatchewan. The contact with the overlying First White Specks is identified by a sharp deflection on the geophysical logs and is observable in several core samples. The Medicine Hat is thickest in the southwest and thins northward and eastward. The Govenlock Member, as defined by Gilboy (1996), is identified on a resistivity shoulder beneath the Medicine Hat Member where the Niobrara becomes muddier. The lower interval (Verger Member; Nielsen, 2003) characteristically contains several bentonite beds which thin and decrease in number toward the northeast.
The Niobrara shows a relatively abrupt northeastward thinning. It is thickest (147 m) in the most southwesterly well, of the study area (well 1, Cube Bay Shore 14-14-5-27W3, Figure 2) and thins to less than 16 m in one of the northeastern wells, Bankeno et al Thunder Creek 10-33-20-5W3 (well 31 in Figures 4 and 5). The rapid tapering of the Niobrara is a result of truncation on a pre-Milk River erosional surface leading to a loss of the First White Specks east of Rge 8W3 along Tp 5, east of Rge 9W3 along Tp 12, and east of Rge 20W3 along Tp 21. The Medicine Hat and Govenlock members also thin northeastwards, independently of the sub Milk River contact. Examination of the Christopher et al. (this volume) cross-section A-A' along Tp 5 shows that the eastward attenuation of the Niobrara Formation renders it virtually indistinguishable from the underlying Carlile Formation and, as such, vestigial remnants of the Niobrara, if present, are incorporated into the Carlile east of Rge 15W2M along Tp 5. Christopher et al. (this volume) also note that in well Imperial Findlater 16-04-021-25W2, just to the east of this paper’s cross-section C-C', the Niobrara is absent. This absence is supported by core evidence.
3. Carlile Formation The Carlile Formation has been recognized informally in Saskatchewan since Gilboy (1989) correlated the non- calcareous shales underlying the Niobrara with Carlile shales in the U.S.A. (Rice, 1981). Nielsen (2003) identified a composite type section at Deer Creek in the Sweetgrass Hills in Montana. The Carlile is defined as the non- calcareous mudstones, siltstones and shales, occasionally capped by sandstones (Gilboy, 1996), that lie between carbonates of the Second White Specks Formation and clastic rocks of the overlying Niobrara Formation. The formation is recognizable on logs as a muted funnel-shaped unit on the resistivity curve, with a large increase in resistivity at the top compared to the resistivity of the overlying bentonite-rich Govenlock. Although the literature describes the non-calcareous nature of these sediments (Gilboy, 1993, 1996; Nielsen, 2003; Pedersen, 2004), the Renaissance Wymark 9-20-12-13W3 core suggests otherwise (well number 17, Figure 3). Gilboy (1996) subdivided the Carlile into three units, of which part of the uppermost unit is cored in Renaissance Wymark 9-20-12-13W3. The core can be broken into three sub-units (Figure 6) as follows:
Renaissance Wymark 9-20-12-13W3 (843.0 to 861.0 m cored)
Carlile Formation
Upper Sub-unit:
843.0 to 844.6 m Marlstone, dark grey, very calcareous, with frequent thin 1 to 2 cm thick beds with higher calcite content. Total calcareous content increases downward to 844.6 m. Specks of very fine shell fragments and possible coccoliths. Scattered millimetre-thick laminae of carbonaceous
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141/09-20-012-13W3/00 Upper sub-unit Renaissance Wymark 9-20-12-13 844.68 to 844.80 m
KB 906.5 m Carbonate interval
600
Lea Park Upper sub-unit 845.78 to 845.94 m laminated
marlstone
700
Milk River
Upper and Middle sub-unit 849.85 to 800 849.96 m contact point at
Niobrara 849.94 m
Carlile Middle sub-unit 900 2WS 851.20 to 851.30 m bioturbated silty shale
Lower sub-unit 856.20 to 856.35 m dark grey shale
Figure 6 - Geophysical log and core photographs of the uppermost Carlile Formation in Renaissance Wymark 9-20-12-13W3 (well 17). Three distinct lithological sub-units are recognized. 2WS, Second White Specks.
Saskatchewan Geological Survey 6 Summary of Investigations 2006, Volume 1 black shale. Blue-grey bentonite (2 cm thick) with visible biotite flakes at 843.2 m. Minor Inoceramus fragments. Gradational contact into: 844.5 to 844.74 m Limestone, dense, medium grained, argillaceous. Gradational contact into: 844.74 to 849.94 m Marlstone, dark grey, very calcareous, with thin 1 to 2 cm thick beds of dark grey carbonaceous shale. Total calcareous content decreases downward to 849.94 m. Scattered specks of very fine shell fragments and possible coccoliths. Towards base, percentage of specks decreases and specks occur only in thin (millimetre-thick) laminae. Occasional pyrite crystals. Starved sediment ripple at 849.23 m. Sharp contact at:
Middle Sub-unit:
849.94 to 849.96 m 2 cm-thick conglomerate of shell debris, possible black chert, fish scales and fragments. Calcite-rich zone. 849.96 to 855.54 m Medium grey noncalcareous silty shale, weakly to moderately bioturbated, with 1 to 3 cm- thick muddy siltstone intervals. Moderately bioturbated shales are siltier. Very rare shell fragments concentrated in thin 1 to 2 mm-thick laminae. Gradational contact into:
Lower Sub-unit:
855.54 to 857.85 m Medium to dark grey non-calcareous blocky shale, with thin (<1 cm thick) discontinuous silty intervals. 857.85 to 861 m Lost core. The contact (not cored) between the overlying Niobrara and the Carlile appears sharp on geophysical logs. No core of this contact is available in the study area. Gilboy (1993) interpreted the top of the Carlile as unconformable with the overlying Niobrara based on correlations north of Tp 25, and also noted anomalous thinning and thickening in the 5-21W3 area. Similarly, Nielsen et al. (2003) also suggest the presence of erosional irregularities. Cross-sections A-A′, B-B′ and D-D′ (Figures 2, 3, and 5, respectively) show minor regional variations in the thickness of the Carlile, with more pronounced eastward thinning observed in the most northerly cross-section C-C' (Figure 4) where the easternmost Carlile is about half as thick as it is in the westernmost well.
4. Summary The Niobrara thins abruptly in a northeasterly direction as a result of an unconformity at or near the base of the overlying Milk River. The Medicine Hat Member appears to thin independently of the sub–Milk River contact. Although the Carlile is somewhat variable in thickness, it shows no real appreciable west to east changes in the wells chosen for the cross sections along Tps 5 and 11, but thins northward as evidenced in cross-section D-D'.
The preliminary cross sections generated for this study show significantly different relationships between the Milk River, Niobrara, and Carlile than those previously established. Further work is currently underway to gain a more complete understanding of the Upper Colorado Subgroup.
5. Acknowledgments The authors thank Dr. J. Christopher for his valuable guidance, patience, and readiness to share his vast wealth of geological knowledge. Megan Opseth and Millie Conlan are thanked for their help with the painstaking task of drafting the cross sections. Andrew Nimegeers’ editorial comments have greatly improved this paper.
6. References Gilboy, C.F. (1989): Upper Cretaceous stratigraphic cross-sections (Fish-scale sandstone to Milk River Formation ) in S.E. Alberta, S.W. Saskatchewan and N. Montana; with Summary of Investigations 1989, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 89-4. ______(1993): The Carlile Shale equivalent (Upper Cretaceous) in southwestern Saskatchewan: A wireline- log study; with Summary of Investigations 1993, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 93-4.
Saskatchewan Geological Survey 7 Summary of Investigations 2006, Volume 1 ______(1996): Detailed log-based stratigraphic of the Colorado Group and Milk River strata (Cretaceous), southwestern Saskatchewan; in Summary of Investigations 1996, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 96-4, p133-135. Hancock, W.P. and Glass, D.J. (1968): Medicine Hat Gas Field, Alberta and Saskatchewan; in: Beebe, B.W. (ed.), Natural Gases of North America, Volume 1, AAPG, Mem. 7, p731-735. Kendall, A. and Simpson, F. (1974): Calcite layers in the uppermost Medicine Hat Sandstone (Upper Cretaceous) of southwestern Saskatchewan; Bull. Can. Petrol. Geol., v22, p34-41. Marsh, A. and Heinneman, K. (2005): Stratigraphic and Hydrogeologic Framework of Western Saskatchewan, URL
Pedersen, P.K. (2004): Shallow gas research project in southeastern Saskatchewan: Revised lithostratigraphy of the Colorado Group and reservoir architecture of the Belle Fourche and Second White Specks in the Senate Pool; in Summary of Investigations 2004, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2004-4.1, CD-ROM, Paper A-16, 15p.
Rice, D.D. (1981): Subsurface cross section from southeastern Alberta, Canada to Bowdoin Dome area, north central Montana showing correlation of Cretaceous rocks and shallow, gas productive zones in low- permeability reservoirs; U.S. Geol. Surv., Oil and Gas Investigations, Chart OC-112.
Simpson, F (1981a): Lithologic Descriptions of selected core sections from the Colorado and Montana Groups (Middle Albian to Campanian) of Saskatchewan; Sask. Miner. Resour., Rep. 233, 72p.
______(1981b): Low-permeability gas reservoirs in marine Cretaceous sandstones of Saskatchewan II. Well- log analysis of Medicine Hat Sandstone (Santonian) of southwestern Saskatchewan and southeastern Alberta; in Summary of Investigations 1981, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 81-4, p149-153.
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