Study on Enhanced Oil Recovery Technology in Low Permeability Heterogeneous Reservoir by Water-Alternate-Gas of CO2 Flooding

Abstract

Abstract The common problems that water injection come across in low permeability heterogeneous oil reservoir are poor injectability, low production, high water cut and low oil recovery. The previous studies showed that Water-Alternate-Gas (WAG) of CO2 flooding could enhance oil recovery in low permeability oil reservoir effectively. However, the way to use effective technology to enhance oil recovery and net present value (NPV) in low permeability heterogeneous oil reservoir became a difficult point in WAG flooding. This paper introduces allocation of injection rates (AOIR), tapered Water-Alternate-Gas (TWAG) and AOIR-TWAG to study the feasibility of the technologies in enhancing oil recovery with numerical reservoir simulation base on the previous studies. The development effects of constant WAG in the reservoirs with different variation coefficients were contrasted. And the feasibility of the three technologies to enhance oil recovery was studied. The results show that the development effect of constant WAG flooding is better than that of continuous gas injection with the increasing of the variation coefficient. And the oil recoveries of the three technologies are better than that of the constant WAG flooding. However, only the NPV of the AOIR and AOIR-TWAG are better than that of constant WAG flooding. An actual oil reservoir model of Xinjiang oil field in China was used to check the feasibility of the two technologies. The results show that the oil recoveries and NPVs of the two technologies are better than that of constant WAG flooding. This result proves that the conclution of the reservoir conceptual model is reliable, and the technology could be suitable for other similar low permeability heterogeneous oil reservoirs.