Steam—CO 2 drive experiments using horizontal and vertical wells

Abstract

Research into the application of a simultaneous steam—CO 2 drive process and the examination of vertical and horizontal injection—production well configurations was conducted in a physical model of 1/12th of an inverted regular seven-spot pattern to determine the recovery performance of 12.4°API heavy oil. Three groups of well configurations were mainly investigated: a vertical injection and production wells scheme (group 1), a vertical injection and horizontal production wells scheme (groups 2A and 2B), and a horizontal injection and production wells scheme (groups 3C and 3D). A total of 17 experiments of which having five steam-alone and twelve steam—CO 2 processes were conducted for the above well configurations. In steam-alone tests, the vertical injector and horizontal producer scheme (group 2B) supplied a higher recovery than that of the others. The oil recovery was 33.6% of original oil in place (OOIP) in group 2B compared to 7.8% of OOIP for the vertical injection and production wells scheme (group 1) at 1 pore volume (PV) of steam injected. The lowest ultimate recovery was obtained from the horizontal injector—horizontal producer well configuration (group 3C). For steam—CO 2 tests, oil recoveries were 58.3% and 25.3% of OOIP for a CO 2/steam ratio of 14.2 dm 3/l in group 2A and the horizontal injector and producer (group 3C) with a CO 2/steam ratio of 13.4 dm 3/l, respectively. The co-injection of CO 2 with steam increased the ultimate oil recovery and the production rate over steam alone. The recovery efficiency of horizontal injector—horizontal producer (group 3C) was also the lowest one, but vertical injector—horizontal producer (group 2A) gave the best performance when compared to other tests. When steam-alone and steam—CO 2 tests were compared, the oil recovery increased with increasing CO 2/steam ratio till an optimum value was reached, after which a diminishing effect was observed. The optimum CO 2/steam ratio for maximising oil recovery was ∼ 14 dm 3/l for all well configurations. Therefore the value of CO 2/steam ratio was one of the important factors which affected the performance of the process. The other factor which influenced the oil recovery was the well type of injector and/or producer whether it is horizontal or vertical. The distance between the wells also affected the efficiency of the process. The primary mechanisms for the mobilisation of oil were viscosity reduction, steam distillation, stripping and gas drive effect of CO 2.