The Evolution of SAGD Technology At East Senlac

Abstract

Abstract Since 1996, EnCana Corporation has been advancing twinwell steam assisted gravity drainage (SAGD) technology at the Senlac Thermal Project in East Senlac, Saskatchewan, Canada. The latest development phase, Senlac Phase C, consists of two 750 m horizontal well pairs (C1 and C2) drilled in Section 11- 040–26W3. Start-up steaming operations were initiated in June, 2001, with injector-producer communication established six weeks later. Both pairs were ramping up to full oil production rates by late July, 2001. Oil production from the C1 well pair through the end of October, 2002 averaged 275 m3/d, with peak monthly rates exceeding 460 m3/d while operating under solvent- aided SAGD (SAP) conditions. Over the same 16-month period, oil production from the C2 well pair averaged 335 m3/d, with peak monthly rates exceeding 420 m3/d under conventional SAGD conditions. Cumulative steam-oil ratios for the C1 and C2 well pairs are 2.7 m3/m3 and 2.3 m3/m3, respectively. Project Description The Senlac Thermal Project, located 100 kilometres south-east of Lloydminster, Alberta, Canada, uses steam assisted gravity drainage (SAGD) technology(1) to recover 12 ° API heavy oil from the Dina/Cummings formation(2), a relatively thin unconsolidated channel sand buried 750 m deep. The channel is made up of highly- permeable oil-saturated sands, with some bottom water present in formation lows. A summary of reservoir properties is given in Table 1. The Senlac facility is a highly-integrated steam generating and oil treating battery. The steam plant is equipped with three 14.65 MW (50 mmBtu/hr) boilers capable of generating 2,000 m3/d of wet steam CWE (cold water equivalent). The wet steam is scrubbed, producing 1,550 m3/d of dry, injection quality steam. The oil treating plant consists of a gravity separator and an atmospheric flash unit for the separation of produced water and oil. The separation units run in series to clean oil production to sales specifications (below 0.5% BS&W). Sales oil is blended with diluent before pipeline transportation. Produced water is disposed into the Duperow formation, a thick carbonate that underlies the Dina/Cummings formation. Early Development Phases The first application of SAGD at Senlac(3–5) began in 1996 with Phase A, an area with 15 m of pay and no bottom water. Phase A initially consisted of three 500 m well pairs drilled with an interwell spacing of 135 m. Vertical spacing between production wells and injection wells averages 5 m. The Phase A wells, denoted A1, A2 and A3, were completed with wire-wrapped screens which produced considerable amounts of sand from the onset. In 1997, a 450 m long infill well pair, A4, was drilled between the A2 and A3 pairs, and completed with 0.457 mm (0.018 in.) keystone-cut slotted liners. This slot design showed improved sand control over the previous screen design. A picture outlining well locations is presented in Figure 1. Phase A has reached the economic limit of production, and all four well pairs are shut in. A summary of Phase A SAGD performance is presented in Table 2.