Extensive Experimental Study of Low-Salinity Waterflooding Using Hele-Shaw Cell: A Focus on Gravity and Mobility Ratio Effects

Abstract

Recently, low-salinity waterflooding (LSWF) has garnered attention as a promising enhanced oil recovery (EOR) method. LSWF implies the injection of a modified-composition brine into oil reservoirs with a promising potential of enhancing the oil recovery. In this study, two-dimensional visualization of oil displacement mechanism during LSWF is performed in a Hele-Shaw cell. A set of comprehensive experiments is conducted to investigate the areal sweep efficiency between different oils and brines as a function of various parameters. The movement in the Hele-Shaw cell is considered similar to two-dimensional flow in porous medium. Various parameters (ionic strength, injection rate, gravity, and mobility ratio) were extensively studied. The effect of ionic strength was studied between seawater (SW) and 1%diluted-seawater (1%dSW). It was indicated that the dilution of SW to 1%dSW has resulted in a lower areal sweep efficiency. This observation suggests the less dominant impact of oil-water interactions during LSWF. The effect of injection rate was studied for low, intermediate, and high flow rates and the results showed a clear increase in oil recovery with the increase of the injection rate. The effect of gravity was studied at different degrees of inclination angles up to 15°. It was clearly observed that the increase of the inclination angle has resulted in a lower areal sweep efficiency. These results showed that the effect of gravity can have a significant impact on the areal sweep efficiency; moreover, it showed a more profound effect on water fingering at the breakthrough. Light and waxy oils were used in this study, which generated varying mobility ratios with different injected brines. The analyzed images illustrated a lower oil recovery at a higher mobility ratio, as it was clearly observed that the injected brines achieved better areal sweep efficiency displacing the light oil as compared to the waxy oil. Most LSWF studies rely on coreflooding experiments to evaluate the performance of the process. Due to the complexity of the interactions between oil/brine/rock, the mechanisms of this process are not yet fully understood. Investigating the LSWF process in the absence of the rock can provide further explanation of the fluid-fluid (brine-oil) interactions. The gravity effect in this type of experiment was generally ignored and including it in this study makes its findings more representative of inclined oil-bearing formations.