Impact of Low Salinity Flooding on Interfacial Properties between Oil/Brine/Calcite : Molecular Scale Investigation
Al Hosani, Mohamed
Chapman, Walter G.
Doctor of Philosophy
Low salinity water flooding (LSWF) has been recognized as a promising method for improving and sustaining oil production due to its cost-effectiveness and low environmental impact. It is believed that injecting water with ionic strength lower than that of the reservoir leads to signiﬁcant changes in the oil/water interfacial tension and ﬂuid/rock interfacial energy which enhances the oil displacement eﬃciency. The additional oil recovery from this method, in principle, relays on rock wettability alteration from oil-wet to water-wet condition. Despite the successful laboratory experiments and ﬁeld trails, several reports have been published claiming the failure of LSWF. However, because of the complex interactions between oil/water/rock sys- tem, the underlying mechanisms for the positive or negative impact of LSWF remain controversial and poorly understood. It has been hypothesized that forces developed within a water thin ﬁlm between the rock and the crude oil control the wettability alteration. These forces are directly related to the thermodynamic phenomenon known as disjoining pressure, which permits the release of crude oil from the rock surface. These forces can presumably be aﬀected by factors such as water chemistry, pH, and surface charge resulting in a change in the interfacial properties as well. Moreover, a few reports have suggested that liquid/liquid interfacial phenomena can cause the break-up of a continuous oil phase into small droplets while ﬂowing through rock pores particularly under the water-wet condition. Consequently, oil might be trapped in small pores media reducing the oil production during LSWF. Hence, in this thesis, as a first step toward understanding the problem, molecular dynamics simulation is used to (i) investigate the impact of potential determining ions (PDIs) at different ionic strengths on interfacial properties between oil/water/calcite system,(ii) understand the ﬂow behavior of fluid (water and oil) through calcium carbonate nano-pore, and (iii) finally, investigate the detachment of different oils from different calcium carbonate surfaces using low and high water salinities at reservoir condition. An important progress has been made in understanding the impact of PDIs on different major properties for oil/water/calcite system. These properties are essential factors that help to get fundamental insights on the mechanisms responsible for enhancing oil recovery during LSWF. Additionally, the molecular frameworks developed throughout the thesis have set the stage for MD simulations to improve the understanding on the mechanisms responsible for enhancing oil recovery during LSWF. In addition to that, the presented approaches can have potential application in predicting the enhanced oil recovery performance via nano-ﬂuid or surfactant injection in petroleum reservoirs.
Low salinity water flooding; Molecular dynamics simulations; Potential determining ions; oil snap-off.