Numerical simulation and sensitivity analysis of gravity-assisted tertiary gas-injection processes

Corefloods and field investigations confirm that a large amount of incremental tertiary oil can be recovered from dipping waterdrive reservoirs using gravity-assisted tertiary gas-injection processes. These processes include the double-displacement process (DDP) and the second-contact water-displacement (SCWD) process. The DDP consists of injecting gas into waterflooded oil zones. The SCWD process consists of submitting these gasflooded zones to a new water-displacement process. Reservoir simulations performed with an adaptive-implicit simulator were applied to investigate the macroscopic mechanisms of the two processes. The effects of several important parameters on the performance of the DDP were studied to optimize the oil production of the process. Moreover, the SCWD process was simulated to investigate its feasibility. The results show that both processes are efficient methods for recovering the residual oil to water. A good representation of the laboratory results was obtained through the simulations. It was confirmed that oil-film flow plays a very important role in achieving high recovery efficiencies in the DDP. In the SCWD process, trapped gas reduces the possibility of the residual oil being trapped in the center of pores in the secondary water invasion. Consequently, residual oil can be recovered quickly by a second waterflood. Therefore, the SCWD process is suitable for application in situations in which the source of gas is not sufficient, and where the formation has a high irreducible gas saturation.