Experimental Investigation of Low-Salinity Water Flooding in a Low-Permeability Oil Reservoir

Abstract

Low-salinity water (LSW) flooding has become a quite simple, effective, and economically feasible enhanced oil recovery (EOR) technology under the background of low oil price. The B425 block with a low permeability in Shengli oilfield, China, has achieved an excellent LSW flooding performance, but the main EOR mechanisms in the block are still not clear. Therefore, in order to investigate the LSW flooding mechanisms in the B425 block, a set of core-flooding experiments were conducted. The water contact angle on core slice and the zeta potential of rock particle were also measured. Then the main EOR mechanisms of LSW flooding in the block were discussed. The experimental results show that the LSW injection can indeed enhance the oil recovery in the low-permeability oil reservoir. Compared with the direct high salinity water (HSW) injection, direct LSW injection and HSW–MSW (medium salinity water)–LSW successive injection can increase the oil recovery factor by 10% and 29.52%, respectively (when the core permeability is about 0.5 md). The water wettability of rock can be strengthened when the LSW is injected. This can be demonstrated by the right shift of oil–water relative permeability curves, the increase of Ca2+ and Mg2+ concentrations in the produced water, and the reduction of both water contact angle and zeta potential of rock particles during core flooding or in the LSW environment. Clay particle migration was also observed during core flooding. It can be verified by the direct evidence of the produced water containing many clay particles and the indirect evidence of the identified abnormal increase in the displacement pressure. Overall, the EOR performance of LSW flooding in the B425 block is remarkable, which has brought great confidence for the low-permeability oil reservoirs to conduct the LSW flooding in China.