Novel Insights into Low Salinity Water Flooding Enhanced Oil Recovery in Sandstone: The Clay Role Study

The ever-growing global energy demand and natural decline in oil production from mature oil fields over the last several decades have been the main incentives to search for methods to increase recovery efficiency. This paper quantifies the clay role and the important role of pH in the water flooding of low salinity water in sandstone with and without clays as a function of temperature. Four chromatography columns containing different amounts of sand, illite, and kaolinite (100% sand; 5% Illite, 95% sand; 5% kaolinite, 95% sand; 2.5% Illite, 2.5% kaolinite, 95% sand) were water flooded with various salinities at four different temperatures 25, 70, 90 and 120 °C. Effluent concentrations of Ca²⁺ and CH₃COO⁻, and pH were measured. The system was pre-aged for a week at 70 °C with 0.01 molar (M) sodium acetate to simulate the bonding of oil-bound carboxylic acids with the reservoir. Desorption of carboxylic groups from reservoir clay surfaces is thought to be an important control over low salinity EOR water injection and its extent should depend on pH. To quantify the impact of the presence of the clay, a clay-free sample was also used, the acetate release and Ca²⁺ desorption were in some cases higher than those observed in non-clay free samples. Typically, cores with higher clay content saw a great rise in pH, but the clay-free samples also saw a rise in pH, as great as that of the clay-containing cores.