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

Abstract

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.

Debunking the Impact of Salinity on Crude Oil/Water Interfacial Tension

“…50−53 It was observed during LSWI that polar species of crude oil such as asphaltenes and naphthenic acids can promote the formation of microdispersion leading to wettability alteration accordingly. 9,43,44,54,55 Therefore, studying the oil/water interface of crude oil samples with different physicochemical properties and improving our knowledge about the main responsible surface-active materials at the interface are extremely important.…”

“…The studies conducted by Sanyal et al , showed that the polar species of crude oil (asphaltenes molecules with various polycyclic aromatic rings) and the ions in injection water would influence the performance of LSWI. However, the LSE on the oil recovery has been shown not only for rocks composing of other clay minerals (i.e., chlorite, illite, and muscovite) but also for sandstone rocks free of clay minerals. − It was observed during LSWI that polar species of crude oil such as asphaltenes and naphthenic acids can promote the formation of microdispersion leading to wettability alteration accordingly. ,,,, Therefore, studying the oil/water interface of crude oil samples with different physicochemical properties and improving our knowledge about the main responsible surface-active materials at the interface are extremely important.…”

Adsorption of Polar Species at Crude Oil–Water Interfaces: the Chemoelastic Behavior

“…In particular, the interfacial properties of crude oil have received significant attention over the past decades because of their relevance to oil recovery, transport, and processing. − For example, most oil extraction processes are based on injecting water-based liquids, called brines, into the porous oil reservoir. The efficiency of this process, known as waterflooding, is generally understood as an interplay between viscous and interfacial forces, and it has been shown that it can be enhanced by tuning the chemical composition of the brine, for example, by reducing its salinity or by selectively increasing the concentration of certain divalent ionic species. − However, despite intense research in this field, the underlying mechanisms that lead to improved oil recovery are still debated. − Moreover, the complex rheology of the interfacial films dictates the stability of oil/water emulsions, with implications in oil transport, processing, and final quality. , …”

Direct Insight into the Cause and Time Evaluation of Spontaneous Emulsification of Water in Crude Oil during Low Salinity Waterflooding Using Microfluidic Model

“…They found out that water-in-oil dispersions led to oil swelling and wettability alteration. They concluded that crude oils’ tendency to form microdispersions could be an essential screening method for oil reservoirs before waterflooding . The swelling of the oil droplets during LSW injection has been confirmed by some other reserachers .…”