Reservoir Characterization of the Wabiskaw B in the Kirby Area, Alberta, Canada

Abstract

Summary An integrated geological and engineering framework of the Kirby Wabiskaw B reservoir has permitted a retrospective analysis of two steam flood pilots that failed to achieve commercial success. The analysis identified four factors that negatively impacted the pilots and which would need to be addressed prior to future steam floods. The factors are: Laterally extensive calcite cemented horizons, interbedded mudstones, pore plugging kaolinite and clay diagenesis upon contact with steam. Introduction Beginning in the late 1990's, and continuing to 2005, significant debate has raged in Alberta on the advisability of permitting the depletion of gas overlying immobile bitumen. Unlike conventional oil recovery, depletion of a gas cap does not directly affect reservoir drive for bitumen. In a steam flood, the overlying gas creates a pressure blanket that prevents steam escaping from the bitumen zone. Owners of the bitumen rights assert that the bitumen represents the greater asset to the Province of Alberta and that gas production should not be permitted until such time as the bitumen is recovered. In general, it has been accepted that a minimum of 10 metres of bitumen pay is required for thermal recovery. The authors were commissioned to conduct a widespread and detailed examination of the bitumen deposits in the Kirby area to map regions of exploitable bitumen and, by extension, where the gas may be produced in those regions of thin, non-exploitable bitumen. Over 1000 well were evaluated in the study with bitumen, gas, and water thicknesses mapped and hydrocarbon saturations determined. Cores from over 40 wells where described in detail with 16 thin sections collected from 4 of these wells. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were performed on 7 samples to determine clay types and distribution within the reservoir. Isotopic analysis was undertaken on 5 samples of calcite cements to determine stable isotope (carbon and oxygen) composition. Our work compliments the more extensive petrographic, SEM and XRD work of Dekker et al1, Beckie and McIntosh2, and Shier3. Our stable isotope investigation of calcite cements augments the work of Shier3. Analysis of permeability and bitumen saturation of cored wells within Townships 73–74 Range 8W4M and from two steam pilots in section 29–73–7W4M and section 1–73–6W4M was also undertaken. These analyses were compared with bitumen saturations and permeabilities from core in the Hilda Lake Clearwater SAGD pilot (Township 64 Range 3W4M). Engineering appraisal was undertaken on the two pilot sites (IHOP and PHOP Fig. 1) in the Wabiskaw B Formation and at the Cold Lake and Hilda Lake sites in the Clearwater Formation (Townships 64–65 Range 3 W4M). The result was a refined geological framework which permitted a retrospective understanding of the two Wabiskaw B steam flood pilots that, while each having in excess of 20 metres of bitumen pay, failed to achieve commercially viable production rates. This paper examines the geological and engineering evidence on macro, meso, micro and molecular levels, each of which contributes to the explanation of the performance of the pilots. The Wabiskaw B reservoir, within the Kirby area of Alberta (Townships 71–75 Ranges 3–10), occurs between the Cold Lake thermal recovery projects to the south and the Athabasca bitumen mining projects to the north (Fig. 1)The Wabiskaw B is a significant bitumen resource with total pay of over 30 metres in the thickest part of the reservoir. Viscosity of the bitumen varies from 30,000 to 82,300 mPa necessitating thermal recovery techniques. Upon first examination, the log characteristics appear comparable to the successfully steam flooded Cold Lake Clearwater reservoir in Townships 64 - 65, Range 3W4M (Fig. 2).