PRODUCTION PERFORMANCE COMPARISON BETWEEN WATER ALTERNATING GAS AND DOUBLE DISPLACEMENT PROCESS

Abstract

Water alternating gas process (WAG) and double displacement process (DDP) are two effective methods to recover oil in the reservoir as they combine the advantages of water and gas injection. In this study, reservoirs with different dip-angles are constructed by the reservoir simulation software. The effects of different operating parameters are investigated for WAG with up-dip and down-dip injection and DDP by using barrel of oil equivalent (BOE) as an indicator. Low water cut criteria, high water injection rate, moderate gas injection rate, and shorter injection durations of water and gas are considered to be beneficial for the two types of WAG. Moreover, the increase of water to gas injection duration ratio enhances the oil production performance in a non-dipping reservoir while this ratio does not have a significant effect for an inclined reservoir. We can improve the performance of DDP by using low water cut stopping criteria for water flooding and injecting water and gas at high rates. The best performance process for all reservoirs is WAG. Although DDP yields higher oil recovery factor than WAG, it consumes much larger amount of gas which results in lower BOE. The optimum production processes for a non-dipping reservoir, a 15º dipping reservoir, and a 30º dipping reservoir are (1) WAG with up-dip injection by eight vertical wells, (2) WAG with down-dip injection by two horizontal wells, and (3) WAG with up-dip injection by a vertical well up-dip and a horizontal well down-dip. Sensitivity analysis shows that the higher horizontal permeability results in the higher oil recovery factor in an inclined reservoir. The increase of kv/kh ratio improves the oil production whereas the decrease of kv/kh ratio requires much more amount of injected gas due to the earlier breakthrough. For the three-phase relative permeability correlation, ECLIPSE default model gives more oil recovery factor than Stone 1 and Stone 2 models. We can produce oil from the thinner reservoir in shorter time but not always with more efficiency. Light oil containing large amount of solution gas is easy for production.