Wimborne Project

An Integrated Study of Beaverhill Lake Group


Summary:
Location: T21-43, R14W4-10W5
Strata: Beaverhill Lake
Year of Study: 1993


Introduction

The study area for this report extends from Twp 20, Rge14W4 in the southeast to Twp 43, Rge10W5 in the northwest. It was chosen to allow a thorough evaluation of the Wimborne/Twining area in the context of the larger regional framework of the Beaverhill Lake Basin in west central Alberta. The area includes the giant Swan Hills gas field at Caroline, as well as the transition from Caroline's classical style of Swan Hills build ups, that have been the traditional targets of the energy industry, to the regional carbonate bank style of deposition that characterises southern Alberta. The transition between these two depositional settings has been poorly understood until recently, due to an almost total lack of well control in the critical Cremona and Innisfail areas.

The Wimborne and Twining areas had been overlooked until several wells were released in late 1991. These wells - Mobil 7-32-32-28W4 and Unocal 6-2-34-26W4 - proved that Swan Hills buildups were present much further north than had previously been thought. The Unocal well indicates that these buildups were in pressure systems isolated from the regional carbonate bank to the south. Previous exploration in the area by Quintana, at 6?11-33-24w4, proved the presence of light oil in the area when a show of 41.2o A.P.l. oil was analysed from a drillstem test. The oil show came from an interval that is the equivalent of the producing Swan Hills interval at Caroline. Recognition of the oil show and the potential for isolated Swan Hills atolls to be found in the Wimborne area were the stimulus that resulted in this study.

The Swan Hills Formation in the study area has been divided into six cycles, the first three of which have been grouped for mapping purposes as the Light Brown Cycle. This interval exhibits consistently lighter matrix colour than other Swan Hills cycles. The top of the Swan Hills Light Brown Cycle is marked by an abrupt, diastemic break that can be traced across the study area wherever there is sufficient carbonate buildup. Based upon conodont samples taken from 15 wells in the study area and the intertonging of the basinal members of the Waterways Formation, the development of the Swan Hills Light Brown Cycle is believed to have originated during the equivalent of Christina time and ended during the during early to middle Moberly time. This time frame is also applicable to the producing interval at Caroline, where similar fauna, diastemic breaks, and bank to basinal shale transitions are found.

The primary differences between the Caroline area and the Wimborne area are twofold:

  1. Caroline has undergone extensive dolomitization and leaching of the organics as a result of Replacement Matrix Dolomitization (RMD), while at Wimborne the Swan Hills reservoir is limestone, and it is highly unlikely that a dolomite reservoir has developed in this area.
  2. Subsequent cycles of the Swan Hills Fm. prograde at Wimborne toward the northwest over the earliest, or oldest, basinal sediments of the Christina and Moberly Members of the Waterways Fm. These sediments were deposited as a combination of stillstand deposits and rapidly clinoforming argillaceous limestones or "shales" as they appear on gamma logs. To the west, a starved basin setting developed on the eastern flanks of the Caroline and Cremona carbonate banks. As the subsequent younger cycles of the Swan Hills were deposited in these areas they were confined to growing on the pre-existing carbonate buildups and typically backstep to the west with each younger cycle.
These differences can be related to:
  1. the maximum depth of burial, as related to temperature and pressure, and depositional facies of the Light Brown Cycle; and
  2. the paleogeographic setting, including probable wind and current directions, sediment supply and basin geometry. The net result is that Caroline is a relatively simple and highly prospective area that deserves further exploration to fully evaluate the hydrocarbon potential of the Light Brown Cycle. Although the Wimborne area is slightly more complex due to the offlapping younger cycles of the Swan Hills, it has excellent potential for trapping light oil.

For more information contact:

Leslie Sears
Petrel Robertson Consulting Ltd.
500, 736- 8th Avenue S.W.
Calgary, Alberta
T2P 1H4

Phone: (403) 218-1618
Fax: (403) 262-9135
lsears@petrelrob.com
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