Unlocking Bitumen in Thin and/or Lower Pressure Pay Using Cross SAGD (XSAGD)

Abstract

Abstract Cross SAGD (XSAGD) is similar to SAGD except that the horizontal injection wells are placed perpendicular to the horizontal production wells. Some completion restriction near the points where the wells cross can be included in the initial well completions or added later to limit short-circuiting of steam between the wells. The concept of XSAGD as applied in a 20-metrethick homogeneous sand was introduced in the November 2005 International Thermal Operations and Heavy Oil Symposium in Calgary, Alberta. Expanding beyond that presentation, this paper describes simulations showing that XSAGD offers advantages over SAGD for developing thin and/or low-pressured bitumen sands. By combining both gravity drainage and lateral displacement, XSAGD can accelerate recovery, reduce steam requirements and improve economic potential compared to SAGD. Simulation results are discussed comparing SAGD and XSAGD performance for pay thickness from 10 - 40 metres, for pressures ranging from 1,500 - 4,500 kPa, and for homogeneous and heterogeneous pay. Introduction An earlier study(1) describes how XSAGD combines lateral displacement with gravity drainage to accelerate bitumen recovery compared to the SAGD(2) concept in a 20-m homogeneous sand. Some form of completion restriction near where the injection and production wells cross is necessary to limit short-circuiting of the steam and to promote lateral displacement. This restriction could be added after initial communication is established between the wells or it could be built in from the beginning. The recovery acceleration for XSAGD is partially related to the increased drawdown that can be applied to the producing wells while still maintaining effective steam-trap control. This benefit is due to the lateral offset between the active sections of the completions and the tendency for steam to gravity-override before reaching the unrestricted sections of the producing wells. Overall, XSAGD accelerates bitumen recovery and lateral expansion of the steam chamber and reduces cumulative steam oil ratio (CSOR) compared to SAGD. However, XSAGD recovery factor (RF) generally is slightly lower than SAGD RF. The capital costs for wells, pads and facilities should be essentially the same for both processes even though the pad arrangement may be somewhat less flexible for XSAGD.