EFFECT OF PH ON THE DOMINANT OIL RECOVERY MECHANISMS BY LOW SALINITY WATER

Abstract

Low-salinity waterflooding (LSWF) in carbonate formations can alter wettability to more favorable conditions and increase oil recovery. LSWF performance depends on various parameters, such as temperature, oil composition, formation water and imbibing fluid, mineralogy, and pH. The variation in pH value affects the performance of LSWF. However, several studies regarding the effect of pH on LSWF performance showed different and contradicting results. Therefore, this study is aimed to investigate the influence of the pH value of the imbibing brines on the performance of LSWF, along with the detection of the proposed mechanisms. In this thesis research, experimental studies such as ion chromatography analysis, contact angle measurement, coreflooding experiment, spontaneous imbibition test, pH measurements, and zeta-potential measurements have been conducted to investigate the effect of pH on the active mechanisms during LSW and find the optimal concentration of LSW solution. The study is to consider two cases, which include applications of LSW brines with initial pH values of <7 and >7. Wettability alteration by LSW has been achieved and compared between high and low pH cases. High pH brines acted more efficiently on the wettability alteration. The spontaneous imbibition test resulted in similar production by applying high and low pH brines. However, the recovery rate varied due to the order of activated mechanisms. An increase in pH value and calcium ions during spontaneous imbibition and contact angle measurements proved the presence of a rock dissolution mechanism. Conduction of coreflooding experiment with high pH brines showed 24% incremental recovery achieved due to alkali effect mechanism activation. The produced fluid form supports the activity of the formation of microemulsions mechanism. According to the results of ion chromatography analyses and zeta-potential measurements, mainly accepted mechanisms, such as multicomponent ionic exchange and expansion of the electrical double layer, have not been observed. The optimal LSW concentration was found to be a 2.3-times diluted seawater, which is a Caspian seawater salinity concentration