Novel Insights into the Pore-Scale Mechanism of Low Salinity Water Injection and the Improvements on Oil Recovery

The long-held industry view that the Low Salinity Effect (LSE) depends mainly on rock-fluid interactions has led to failures and successes that can be explained by fluid-fluid interactions. Therefore, elevating our knowledge about the microscopic interactions occurring in the crude oil/brine/rock system appears to be of paramount importance. This paper chooses to outline various analytical tools in combination with a microfluidic instrument (Micromodel) to identify these interactions at simulated reservoir conditions for the first time (temperature and pressure of 50 °C and 2000 psi). In this study, six crude oil samples have undergone testing for microdispersion quantification and surface charge evaluation. Microdispersion is a term referring to the spontaneous formation of water clusters (in micrometer sizes) within the crude oil during low salinity water injection (LSWI), which will be elaborated in this study. Despite all samples showing the same trend regarding the negative surface charges, they showed an entirely different propensity toward formation of water microdispersion. The analysis of the oil/water interface by Fourier-transform infrared spectroscopy (FT-IR) led to the understanding that conjugated acidic compounds within the crude oil are the main compounds for the creation of water microdispersions. The Micromodel results revealed the predominant role of microdispersions in oil swelling and wettability alteration in a porous medium leading to an increase in the microscopic sweeping efficiency, thus leading to improved oil recovery. Also highlighted is the pivotal importance of water microdispersion as a screening method for oil reservoirs before waterflooding operation.