An adnavce compositional analysis investigation on the role of crude oil-brine interface reactions on the performance of low salinity water injection

We present a systematic study and examination of the structure of oil/water interface during low salinity water injection (LSWI) through a series of advanced experimental methods. This research will clarify the potential role of different surface-active materials within the crude oil phase, such as asphaltenes and acidic materials, on the low salinity water performance in oil reservoirs. In this study, the microdispersion formation is elaborated as the main mechanism responsible for LSWI regardless of the reservoir rock type. Fourier Transform Infrared (FT-IR) spectroscopy, and Fourier Transform Ion Cyclotron Resonance mass spectroscopy (FT-ICR) were used to detect delicate compositional changes taking place at the oil/water interface as a result of LSWI. Also, Karl Fischer titration (KFT) was performed to understand the mechanism of LSWI and to measure the amount of water microdispersion formed within the crude oil samples. The results show that microdispersion formation, which is elevated dramatically in lower brine salinities compared with higher salinities, is the main mechanism of additional oil recovery by LSWI. It is demonstrated that significant compositional changes take place for crude oil when it comes into contact with low salinity water (LSW) which leads to formation of microdispersion. The acidic materials within the crude oil diffuse into the oil/water interface and react with water molecules. The reactions between acidic materials and water molecules is significantly enhanced when crude oil is in contact with LSW than HSW and this results in formation of water microdispersion in lower brine salinities. The structure of these surface-active materials is studied through FT-ICR MS under negative electrospray ionization (NESI) mode which shows the non-aromatic monoacids are responsible in LSE. We show that the increase in concentration of monoacids at the oil/water interface and the subsequent microdispersion formation during LSWI takes place regardless of the rock effects and they occur as a result of interactions between crude oil and water. Moreover, the oil/water interface in LSWI is saturated with monoacids with 18 carbon number, while the interfacial molecules are constituting of the heavy aromatic hydrocarbon in higher brine salinities. This behavior is explained by solvophobic effect at the oil/water interface at higher brine salinities. The results of this study represent an important step toward understanding the mechanism responsible for the LSE. The knowledge will help the oil and gas industry in the task of evaluating and ranking oil reservoirs for enhanced oil recovery by low salinity water injection.