The Decisive Role of Microdispersion Formation in Improved Oil Recovery by Low-Salinity-Water Injection in Sandstone Formations

Abstract

Summary Efficiency of low–salinity–water injection primarily depends on oil/brine/rock interactions. Microdispersion formation (as the dominant interfacial interaction between oil and low–salinity water) is one of the mechanisms proposed for the reported additional oil recovery by low–salinity–water injection. Using similar rock and brines, here in this work, different crude–oil samples were selected to examine the relationship between crude–oil potency to form microdispersions and improved oil recovery (IOR) by low–salinity–water injection in sandstone cores. First, the potential of the crude–oil samples to form microdispersions was measured; next, coreflood tests were performed to evaluate the performance of low–salinity–water injection in tertiary mode. Sandstone core plugs taken from a whole reservoir core were used for the experiments. The tests started with spontaneous imbibition followed by forced imbibition of high–salinity brine. Low–salinity brine was then injected in tertiary mode. The oil–recovery profiles and compositions of the produced brine were measured to investigate the IOR benefits as well as the geochemical interactions. The results demonstrate that the ratio of the microdispersion quantity to bond water is the main factor controlling the effectiveness of low–salinity–water injection. In general, a monotonic trend was observed between incremental oil recovery and the microdispersion ratio of the different crude–oil samples. In addition, it can be inferred from the results that geochemical interactions (pH and ionic interactions) would be mainly controlled by the rock's initial wettability, and also that these processes could not affect the additional oil recovery by low-salinity-water injection. To further verify the observations of geochemical interactions, a novel experiment was designed and performed on a quartz substrate to investigate the ionic interactions on the film of water between an oil droplet and a flat quartz substrate, when the high–salinity brine was replaced with the low–salinity brine. The results of the flat–substrate test indicated that the water film beneath the oil could not interact with the surrounding brine, which is in line with the results of the core tests.