Evaluation of production performance of selective simutaneous water alternating gas (SSWAG) and gas assisted gravity drainage (GAGD) in steeply dipping reservoir

Abstract

One known process that integrates combined gas and water injection is Selective Simultaneous Water Alternating Gas (SSWAG). SSWAG requires two wells for injecting water and gas separately. A gas injector is usually placed at the bottom of the formation while a water injector is placed at the top with another producer well on the other side of the reservoir opposite these two injectors. One process that utilizes gravity drainage is Gas Assisted Gravity Drainage (GAGD). GAGD consists of placing a horizontal producer near the bottom of the reservoir and injecting gas through existing vertical wells. Injected gas tends to flow to the top of the pay zone and expand in sideward and downward direction. The expansion of gas helps sweep the oil towards the horizontal producer. The study showed that recovery factor of SSWAG and GAGD, implemented in dipping reservoir, falls in range of 50% to 80%. The efficiency depends on design parameters. Oil production is enhanced through SSWAG by injecting gas at high rate together with water at low rate with shorter length of horizontal producer and deepest location of horizontal producer in the downdip side. Locations and lengths of injectors have minimal effect on oil recovery efficiency. For GAGD, oil production is enhanced by using high gas injection rate and longer producer. Gas injector should be located at shallowest depth while oil producer should be at the deepest depth. However, SSWAG might not be suitable to implement in dipping reservoir when compared with GAGD and DDP as it has poorer performance.