Investigation on the micro-flow mechanism of enhanced oil recovery by low-salinity water flooding in carbonate reservoir

Low-salinity water flooding has become a significant way to develop carbonate reservoirs in recent years. Clarifying the micro-flow mechanism of low-salinity water flooding (LSWF) on enhanced oil recovery (EOR) becomes the focus of this issue. In this paper, firstly, we conducted a series of experiments to prove that LSWF can improve the recovery of carbonate reservoirs. And then, a new relative permeability model and water content calculation model are established considering interface micro-forces and capillary pressure. The result shows that the present model has good agreement with the experimental results, which can characterize the micro-displacement mechanism of LSWF. The recovery rate can be increased by 9% compared with the formation water flooding (FWF). Under low-salinity conditions, the wettability of rock surface is changed by the chemical reaction of divalent ions (Ca2+, Mg2+, SO42-), which shows more hydrophilic. And the optimal salinity of the brine range from 1400 mg/L to 3200 mg/L. Besides, LSWF can reduce the residual oil saturation, which is the macro cause for EOR. This study has provided a quick and reasonable guide to know the micro-flow mechanism of LSWF and theoretical basis for development of carbonate reservoirs by LSWF.