Prospect SaskatchewanSaskatchewan Oil Sands New Exploration Targets in Northwestern Saskatchewan

Issue No. 9 February 201419 48

Figure 1 – Map showing the locations of the Athabasca bitumen deposits, Cold Lake heavy oil deposits in Alberta, Lloydminster heavy oil deposits in Alberta and Saskatchewan, and three known bitumen occurrences in Saskatchewan (indicated by red stars); modified from Ranger and Gingras (2006) and Christopher (2003). Through most of the area, the Prairie Evaporite solution edge restricted the majority of the migrating oil from continuing up-dip to the northeast further into Saskatchewan. In the northernmost portion of the Athabasca deposit in Alberta and Saskatchewan, however, the oil bypassed the present-day Prairie Evaporite solution edge, continued up-dip to the northeast and was trapped stratigraphically. Similar stratigraphic traps may exist in discrete sandstone-filled incised valleys up-dip from the Athabasca and Cold Lake deposits south of Simonson Lake area.

INTRODUCTION

Bitumen-saturated Lower Cretaceous Mannville sandstones (oil sands) in the Simonson Lake area in northwestern Saskatchewan were first identified by exploration drill holes in the mid 1970s. Further extensive drilling activity by Oilsands Quest from 2004 to 2008 resulted in the definition of a bitumen resource in Townships 94 and 95, Ranges 24 and 25W3, approximately 50 km north of the Clearwater River near Simonson Lake (PR Newswire, 2010; Kohlruss et al.,

2013). Bituminous sands have also been reported in glacial tills near Peter Pond Lake (Kupsch, 1954) and in Mannville sandstone outcrops along the Clearwater River valley (Paterson et al., 1978; Kohlruss et al., 2010) (Figure 1). The model developed for the Simonson Lake area and information gleaned from the other two bituminous shows can be used to help identify potential new exploration targets in northwestern Saskatchewan.

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GENERAL STRATIGRAPHY

The heavy oil and bitumen deposits in eastern Alberta and western Saskatchewan are hosted within Cretaceous Mannville Group sediments. The Mannville Group consists of a lower Cantuar Formation and an upper Pense Formation. The Cantuar Formation is divided into seven members, which are, from lower to upper: Dina, Cummings, Lloydminster, Rex, General Petroleums, Sparky, and Waseca (Figure 2). The Pense Formation is comprised of the lower McClaren Member and the upper Colony Member. The Dina Member, which is the only unit of the Mannville Group preserved in the Simonson Lake area, is equivalent to the lower portions of Alberta’s main bitumen reservoir, the McMurray Formation. In northwestern Saskatchewan, Dina strata are composed of fluvial sandstones, mudstones, and coals. The overlying Cummings Member (Figure 2), which is not present in the Simonson Lake area due to erosion, is represented by a fining-upward sequence of interbedded sandstones and mudstones and its uppermost portions are equivalent to the Wabiskaw Member located at the base of the Clearwater Formation (Christopher, 2003). Clearwater Formation mudstone forms the “cap rock” for in situ oil sands enhanced oil recovery projects in Alberta and its absence in the Simonson Lake area complicates potential in situ recovery. In northwestern Saskatchewan, the Dina directly overlies the sub-Cretaceous unconformity (Figure 2) which was developed on the Devonian Prairie Evaporite breccia, or the Devonian carbonates of the Winnipegosis Formation, or on the carbonates or mudstones of the Meadow Lake Formation (Paterson et al., 1978; Christopher, 1997; Christopher, 2003; Kohlruss, 2012; Kohlruss et al., 2013). Finally, Quaternary till and glacial lacustrine deposits unconformably overlie the Mannville.

Figure 2 – Correlation of stratigraphic units in northeastern Alberta and northwestern Saskatchewan. The Dina Member is equivalent to the lower portions of Alberta’s McMurray Formation and the uppermost portion of the Cummings Member is equivalent to the Wabiskaw Member located at the base of the Clearwater Formation. Depending on location relative to the Paleozoic sub-crop in these areas, Dina deposits can reside on the Prairie Evaporite breccia, or on Winnipegosis carbonates, or on Meadow Lake carbonates or mudstones.

Figure 3 – Schematic structural cross section through the south Athabasca bitumen deposit and into Saskatchewan. This illustrates the effect of the Prairie Evaporite solution edge on Mannville sediments and the resulting roll-over trap (modified from Ranger and Gingras, 2006). This cross section also illustrates the potential for stratigraphic bitumen trapping along the Mannville Group subcrop edge, up-dip from the Athabasca deposit. This model would assume the Athabasca structural trap was filled to capacity and oil was able to “spill” past the trap and continue up-dip.

TRAPPING MECHANISMS FOR MANNVILLE GROUP BITUMEN RESERVOIRS

Two trapping mechanisms exist in the oil sands region of northwestern Saskatchewan and northeastern Alberta. The northeasterly edge for most of the oil in the southern half of the oil trend is coincident with the Prairie Evaporite salt-solution edge (Figure 1). Vigrass (1968), Ranger (2006), and Ranger and Gingras (2006) all suggest a regional structural trap was created in the Mannville Formation as it rolled over the Prairie Evaporite salt-solution edge and formed a significant anticlinal trap restricting most or all of the oil in the southern portion of the Athabasca bitumen deposit from

migrating further up-dip towards the northeast into Saskatchewan (Figures 1 and 3).

The northernmost portions of the Athabasca deposit, which includes the area north of the Clearwater River outcrops (Figure 1), is not trapped by structural roll-over, but rather by the stratigraphic trapping of oil where permeable Mannville Group sediments have back-filled incised valleys, subsequently on-lapping underlying impermeable Devonian rocks and sealed above by Mannville Group mudstones. For bitumen accumulations to occur east of the regional Mannville structural trap associated with the Prairie Evaporite solution edge, the structural

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roll-over trap was either an incomplete structural barrier and oil leaked through the seal and/or through cross-faults resulting in oil migration beyond the solution edge or, despite being an effective barrier, the hydrocarbon column was large enough to overfill the regional structural trap beyond its spill-point which allowed oil to continue migrating up-dip into Saskatchewan (Figures 1 and 3). Another possibility is that the timing of salt dissolution in the northeast postdates oil migration and thus no structural trap existed and instead oil was trapped stratigraphically in this region (Ranger, 2006).

In the Simonson Lake area, bitumen is hosted in the Dina Member which directly overlies the sub-Cretaceous unconformity and is preserved primarily within a discrete, linear (perpendicular to strike) paleo-topographic low formed on the sub-Cretaceous unconformity. This has been interpreted as an incised- valley system filled first with a veneer of lowstand fluvial sandstones (Figure 4) and then backfilled by transgressive fluvial sandstones, mudstones, and coal (Kohlruss, 2012; Kohlruss et al., 2013). As the transgression continued, it is assumed that, as elsewhere in the Western Canada Sedimentary Basin, the fluvial sediments were then covered by estuarine sandstones and mudstones, followed by deposition of marine mudstones of the upper Cummings Member. The Cummings would have been the upper seal for oil trapped in this area. Post-Mannville Group erosion, including Quaternary glaciation, removed undetermined amounts of sediment which included the Cummings Member (Ranger, 2006; Kohlruss, 2012; Kohlruss et al., 2013). Therefore the Dina is unconformably overlain by Quaternary glacial lacustrine and glacial till deposits with no obvious “cap rock” (Figure 3) (Kohlruss et al., 2010; Kohlruss, 2012; Kohlruss et al., 2013).

Since the oil in the Simonson Lake area had degraded to bitumen prior to erosion of the Cummings, the bitumen was “frozen” in place and did not leak away when the seal was removed.

ECONOMIC POTENTIAL

The presence of bitumen in Mannville outcrops along the Clearwater River valley and in the subsurface north of the Clearwater River near Simonson Lake provides evidence that oil did indeed migrate beyond the present-day Prairie Evaporite solution edge and that further bitumen resources may exist outside of Saskatchewan’s currently defined areas (Figure 1). Furthermore, bituminous sands found in glacial till near Peter Pond Lake may also

indicate bitumen was hosted east of the Prairie Evaporite solution edge (Figure 1). Kupsch (1954) stated that the bitumen-saturated sand blocks in the glacial tills near Peter Pond Lake likely came from the Fort McMurray Athabasca oil sands outcrops, which is supported by evidence of ice flow from that direction (Cofaigh et al., 2010), but ice flow from the northeast has also been mapped by the Saskatchewan Geological Survey (Hanson, Pers. comm., 2013); therefore, the potential for the bituminous-sand block originating in deposits to the northeast also exists. Regardless of the direction, the fragile nature of a bituminous sand block would suggest transportation was short and could imply the source of the bituminous block was likely still east of the Prairie Evaporite salt-solution edge rather than from ~200 km away in the Athabasca River valley outcrop region, regardless of ice-flow direction.

These known occurrences of bitumen in Saskatchewan demonstrate the potential along the oil-migration pathway for additional stratigraphic traps, similar to Simonson Lake, and possibly for structural traps related

Figure 4 – Highly bitumen-saturated pebbly trough-crossbedded sandstone of the Mannville Group in northwestern Saskatchewan (Simonson Lake area). Oilsands Quest OQI-W-27 1AA/05-12-095-25W3, 201.71m (C05J037).

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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 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. For more information or to receive additional copies, please E-mail Dan Kohlruss at dan.kohlruss@gov.sk.ca.

Summary

Reservoir: Unconsolidated sandstones in the Mannville Group, Dina Member.

Trap: Structural and stratigraphic.

Seal: Marine mudstones in the Mannville Group, Cummings Member.

Oil Source: Jurassic Fernie Group shales, Devonian-Mississippian Exshaw Formation.

REFERENCESChristopher, J.E. (1997): Evolution of the Lower Cretaceous Mannville sedimentary basin in Saskatchewan; in Pemberton, S.G. and James, D.P. (eds.), Petroleum Geology of the Cretaceous Mannville Group, Western Canada, Can. Soc. Petrol. Geol., Mem. 18, p191-210.

(2003): Jura-Cretaceous Success Formation and Lower Cretaceous Mannville Group of Saskatchewan: Sask. Industry and Resources, Report 223, CD-ROM.

Cofaigh, C.O., Evans, D.J.A., and Smith, I.R. (2010): Large-scale reorganization and sedimentation of terrestrial ice streams during late Wisconsinan Laurentide Ice Sheet deglaciation; Geol. Soc. Amer. Bull., v122, no5/6, p743-756.

Kohlruss, D. (2012): Stratigraphic architecture and facies analysis of the Lower Cretaceous Dina Member of the Mannville Group in northwest Saskatchewan; unpubl. M.Sc. thesis, Univ. Regina, Regina, 186p.

Kohlruss, D., Marsh, A., Jensen, G., Pedersen, P., and Chi, G. (2010): Lower Cretaceous Mannville Group sandstones in the Clearwater River valley, northwestern Saskatchewan; preliminary observations, bitumen sampling, and mapping; in Summary of Investigations 2010, Volume 1, Saskatchewan Geological Survey, Sask. Ministry of Energy and Resources, Misc. Rep. 2010-4.1, Paper A-1, 13p, URL <http://economy.gov.sk.ca/SOI2012V1_A1>

Figure 5 – Exploration model for potential reservoir sandstone plays. Utilizing the Simonson Lake area as a model for exploration, the bitumen in the Dina Member could be preserved in other locations along the subcrop region in narrow discrete incised valleys with lowstand and transgressive fill.

to salt dissolution. Using the Simonson Lake area as a model, any stratigraphic traps along the Mannville subcrop region would likely be found as discrete linear incised valleys filled with Dina or Cummings Member sandstones, and could be capped with Cummings Member mudstones (Figure 5). Therefore, any oil that bypassed the structural roll-over trap further down-dip may have been trapped up-dip, within these linear sandstone bodies that pinch-out below Cummings Member mudstones and above Devonian strata (Figure 5). Unfortunately, these targets would have been subjected to the same erosional events that affected the Simonson Lake area making preservation of potential reservoir rocks and cap rock dependent upon the amount of post-Mannville erosion that occurred, especially during the Quaternary glaciation.

Kohlruss, D., Pedersen, P.K., and Chi, G. (2013): Structure and isopach mapping of the Lower Cretaceous Dina Member of the Mannville Group of northwestern Saskatchewan; in Summary of Investigations 2012, Volume 1, Saskatchewan Geological Survey, Sask. Ministry of the Economy, Misc. Rep. 2012-4.1, Paper A-5, 12p., URL <http://economy.gov.sk.ca/SOI2012V1_A5>.

Kupsch, W.O. (1954): Bituminous Sands in Till of the Peter Pond Lake Area; Sask. Dep. Miner. Resour., Rep. 12, 32p.

Paterson, D.F., Kendall, A.C., and Christopher, J.E. (1978), The Sedimentary Geology of the La Loche Area, Saskatchewan NTS Sheet 74C; Sask. Dep. Miner. Resour., Rep. 201, 38p.

PR Newswire (2010): Oilsands Quest Provides Bitumen Resource Estimate Update (June 7, 2010); URL <http://www.prnewswire.com/news-releases/oilsands-quest-provides- bitumen-resource-estimate-update-97930894.html>, accessed 28 Jan 14.

Ranger, M.J. (2006), The northeastern sector of the Lower Cretaceous Athabasca oil-sands basin: facies and fluids; in Gilboy, C.F. and Whittaker, S.G. (eds.), Saskatchewan and Northern Plains Oil and Gas Symposium 2006, Sask. Geol. Soc. Spec., Publ. No. 19, p249-256.

Ranger, M.J. and Gingras, M.K. (2006), Geology of the Athabasca Oil Sands, Field Guide & Overview, Field Excursion to the Outcrops and Mine Sites of the Fort McMurray Area; 5th edition, Can. Soc. Petrol. Geol. 120p.

Vigrass, L.W. (1968): Geology of Canadian Heavy Oil Sands: AAPG Bull., v52, no10, p1984-1999.