There are large resources of heavy oil reservoir with high viscosity that cannot be produced by natural depletion. The main obstacle to produce from these large deposits of heavy oil and bitumen resources is the high viscosity of these oils. This large amount of oil can be produced considerably by thermal EOR (Enhanced Oil Recovery) methods. The Steam Assisted Gravity Drainage (SAGD) and Cyclic Steam Stimulation (CSS) process has been found as a promising EOR process to recover bitumen and heavy oils.
In this paper, the SAGD and CSS process were combined together to benefit advantages of both methods. When the wells are shut-in to soak, injectivity of steam during SAGD process will increase. So the chamber can extend more easily to drain the oil toward production wells. During this study, possibility and efficiency of this new method was assessed by simulation study using CMG STARS and sensitivity analysis was conducted to optimize the process. The production performance of this method is compared to conventional SAGD and CSS process.
Simulation results show that with the same steam injection rate, this new method has more oil recovery than conventional SAGD, due to better development of steam chamber into reservoir. Also as a result of lower steam-oil-ratio the production cost is reduced.
Steam Assisted Gravity Drainage (SAGD) and Cyclic Steam Stimulation (CSS) processes have been found as two efficient methods for heavy oil recovery. The Steam Assisted Gravity Drainage (SAGD) using gravity as driving force and a pair of horizontal wells for injection/production ensures both a stable displacement of steam and economical oil production rate . As shown in figure 1, SAGD requires two wellbores. One wellbore continuously injects steam and a second one continuously produces mobilized bitumen and condensed steam. Horizontal wells are used to enhance reservoir access and thus well productivity .