Prospect Saskatchewan Saskatchewan Oil Sands New Exploration Targets in Northwestern Saskatchewan
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Prospect Saskatchewan Saskatchewan Oil Sands New Exploration Targets in Northwestern Saskatchewan INTRODUCTION Bitumen-saturated Lower Cretaceous Mannville 2013). Bituminous sands have also been reported in sandstones (oil sands) in the Simonson Lake area in glacial tills near Peter Pond Lake (Kupsch, 1954) and in northwestern Saskatchewan were first identified by Mannville sandstone outcrops along the Clearwater River exploration drill holes in the mid 1970s. Further extensive valley (Paterson et al., 1978; Kohlruss et al., 2010) drilling activity by Oilsands Quest from 2004 to 2008 (Figure 1). The model developed for the Simonson Lake resulted in the definition of a bitumen resource in area and information gleaned from the other two Townships 94 and 95, Ranges 24 and 25W3, bituminous shows can be used to help identify potential approximately 50 km north of the Clearwater River near new exploration targets in northwestern Saskatchewan. Simonson Lake (PR Newswire, 2010; Kohlruss et al., 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. 19 48 Issue No. 9 February 2014 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 Figure 3 – Schematic structural cross section through the south Athabasca bitumen deposit and into Saskatchewan. This northwestern Saskatchewan, Dina strata are composed of illustrates the effect of the Prairie Evaporite solution edge on fluvial sandstones, mudstones, and coals. The overlying Mannville sediments and the resulting roll-over trap (modified from Cummings Member (Figure 2), which is not present in the Ranger and Gingras, 2006). This cross section also illustrates the potential for stratigraphic bitumen trapping along the Mannville Simonson Lake area due to erosion, is represented by a Group subcrop edge, up-dip from the Athabasca deposit. This fining-upward sequence of interbedded sandstones and model would assume the Athabasca structural trap was filled to capacity and oil was able to “spill” past the trap and continue mudstones and its uppermost portions are equivalent to up-dip. the Wabiskaw Member located at the base of the Clearwater Formation (Christopher, 2003). Clearwater TRAPPING MECHANISMS FOR MANNVILLE Formation mudstone forms the “cap rock” for in situ oil GROUP BITUMEN RESERVOIRS sands enhanced oil recovery projects in Alberta and its absence in the Simonson Lake area complicates potential Two trapping mechanisms exist in the oil sands region of in situ recovery. In northwestern Saskatchewan, the Dina northwestern Saskatchewan and northeastern Alberta. directly overlies the sub-Cretaceous unconformity (Figure The northeasterly edge for most of the oil in the southern 2) which was developed on the Devonian Prairie half of the oil trend is coincident with the Prairie Evaporite breccia, or the Devonian carbonates of the Evaporite salt-solution edge (Figure 1). Vigrass (1968), Winnipegosis Formation, or on the carbonates or Ranger (2006), and Ranger and Gingras (2006) all mudstones of the Meadow Lake Formation (Paterson et suggest a regional structural trap was created in the al., 1978; Christopher, 1997; Christopher, 2003; Mannville Formation as it rolled over the Prairie Kohlruss, 2012; Kohlruss et al., 2013). Finally, Evaporite salt-solution edge and formed a significant Quaternary till and glacial lacustrine deposits anticlinal trap restricting most or all of the oil in the unconformably overlie the Mannville. 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 Figure 2 – Correlation of stratigraphic units in northeastern Alberta and northwestern Devonian rocks and sealed above by Saskatchewan. The Dina Member is equivalent to the lower portions of Alberta’s Mannville Group mudstones. For bitumen McMurray Formation and the uppermost portion of the Cummings Member is equivalent to the Wabiskaw Member located at the base of the Clearwater Formation. accumulations to occur east of the regional Depending on location relative to the Paleozoic sub-crop in these areas, Dina deposits Mannville structural trap associated with the can reside on the Prairie Evaporite breccia, or on Winnipegosis carbonates, or on Meadow Lake carbonates or mudstones. Prairie Evaporite solution edge, the structural 2 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. Figure 4 – Highly bitumen-saturated pebbly trough-crossbedded sandstone of the Mannville Group in northwestern Saskatchewan Post-Mannville Group erosion, including Quaternary (Simonson Lake area). Oilsands Quest OQI-W-27 glaciation, removed undetermined amounts of sediment 1AA/05-12-095-25W3, 201.71m (C05J037). which included the Cummings Member (Ranger, 2006; indicate bitumen was hosted east of the Prairie Evaporite Kohlruss, 2012; Kohlruss et al., 2013). Therefore the solution edge (Figure 1). Kupsch (1954) stated that the Dina is unconformably overlain by Quaternary glacial bitumen-saturated sand blocks in the glacial tills near lacustrine and glacial till deposits with no obvious “cap Peter Pond Lake likely came from the Fort McMurray rock” (Figure 3) (Kohlruss et al., 2010; Kohlruss, 2012; Athabasca oil sands outcrops, which is supported by Kohlruss et al., 2013). evidence of ice flow from that direction (Cofaigh et al., 2010), but ice flow from the northeast has also been Since the oil in the Simonson Lake area had degraded to mapped by the Saskatchewan Geological Survey bitumen prior to erosion of the Cummings, the bitumen (Hanson, Pers. comm., 2013); therefore, the potential for was “frozen” in place and did not leak away when the seal the bituminous-sand block originating in deposits to the was removed. northeast also exists. Regardless of the direction, the fragile nature of a bituminous sand block would suggest ECONOMIC POTENTIAL transportation was short and could imply the source of the bituminous block was likely still east of the Prairie The presence of bitumen in Mannville outcrops along the Evaporite salt-solution edge rather than from ~200 km Clearwater River valley and in the subsurface north of the away in the Athabasca River valley outcrop region, Clearwater River near Simonson Lake provides evidence regardless of ice-flow direction. that oil did indeed migrate beyond the present-day Prairie Evaporite solution edge and that further bitumen These known occurrences of bitumen in Saskatchewan