Improving the Performance of Classic SAGD With Offsetting Vertical Producers

Abstract Both theoretical knowledge and field use of ‘Classic1’ SAGD' have greatly expanded over the last 15 years. During that period only a few modifications of ‘Classic’ SAGD have been proposed. The most successful was use of vertical injectors at Sceptre (now CNRL) North Tangleflags and Strike (now Husky) Bolney. Laterally staggered injectors and producers and perpendicular injectors and producers have been proposed, but have not been successfully field tested. This paper discusses field observations and numerical simulation studies indicating that properly placed vertical production wells can capture a significant amount of oil that is not produced by Classic' SAGD development. These vertical wells could also first be used for steam injection high in the pay, CSS low in the pay, or temperature observation purpose; adding further enhancement to the performance of nearby ‘Classic’ SAGD pairs. Horizontal wells could also be placed to access oil that is ‘missed’ because it is below and beneath ‘Classic’ SAGD pairs, but practical aspects involving drilling, completing, and producing horizontal wells in a non-uniformly heated and depleted environment suggest vertical wells are a better choice. Recent History of SAGD Usage ‘Classic’ SAGD ‘Classic’ SAGD is currently the most discussed and most proposed steam-based exploitation process in Canada. An excellent summary was published in 2001 by the inventor of the process, Dr. Roger Butler(1). Other recent publications have discussed a variety of topics about ‘Classic’ SAGD including: screening criteria(2,3), steam chest containment(4), co-injection of solvents(5,6), optimum pressure regime(7), producer inflow problems(8), effect of solution gas(9), and late life strategies(10). Prior Proposed Spatial Alterations from ‘Classic’ SAGD The literature also contains descriptions of processes for several well orientations altered from the ‘Classic’ SAGD configuration. The most advanced alteration is use of vertical injectors and horizontal producers(11–15). The most successful field project to date using this configuration has been Sceptre (now CNRL) North Tangleflags(16). Another spatial variation from ‘Classic’ SAGD is addition of horizontal CSS wells(17). This configuration contains a horizontal CSS well at the same depth as the SAGD producers, and located in the middle of a ‘typical’ SAGD well spacing, so about 50 meters away from each of the offsetting pairs. Placement of the ‘infill’ horizontal wells at the same depth as the SAGD producers likely leaves unswept oil below that depth, and possibly creates another opportunity for addition of vertical producers. To date only numerical simulation and physical modeling have been conducted, but those results suggest improved energy efficiency and productivity compared to ‘Classic’ SAGD. A third variation of well orientation is Cross-SAGD or XSAGD(18). For XSAGD the injectors are placed above the producers, but perpendicular to them. The objective is to obtain more rapid global sweep of the reservoir between the injectors and producers (i.e. to accelerate oil recovery), and according to numerical simulation of an idealized reservoir this will occur. XSAGD is not designed to access or mobilize the oil located beneath and between the producers that is the target of the vertical wells proposed in this study, and

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