Effect of temperature on mineral reactions and fines migration during low-salinity water injection into Berea sandstone

Abstract

Recent experiments on sandstone rocks found more fines migration at higher temperature. They attributed this to temperature-dependent zeta potential. However, temperature also affects mineral reactions. The present study investigates the effect of temperature on both fines migration and mineral reactions. Two sets of single-phase injection experiments are performed using Berea sandstone sister plugs. In one set of experiments, solutions of NaCl brine are injected at a constant temperature of 25 ◦C, 50 ◦C, or 70 ◦C. In the other set, solutions of CaCl2 brine are injected at a constant temperature of 25 ◦C or 50 ◦C. All plugs are subjected to five sequential injections of the designated brine at salinities 0.684 mol/L, 0.171 mol/L, 0.043 mol/L, 0.0085 mol/L, and 0 mol/L. Permeability at each injection stage is calculated from pressure difference across the core. When NaCl brine is used, the percentage of permeability decrease is found to be 99% at 25 ◦C, 90% at 50 ◦C, and 40% at 70 ◦C. The lower permeability decrease at high temperature is found to be accompanied by a smaller concentration of produced fines. Comparison of scanning electron microscope images taken before and at the end of each experiment shows pore enlargement due to mineral reaction at high temperature, which further explains the lower permeability decrease. Ionic concentrations of Ca2+and Mg2+in the produced water are found to be greater at higher temperature, due to higher reaction rate. With CaCl2 brine, a 7% permeability decrease is observed at 25 ◦C, whereas a 20% permeability increase is observed at 50 ◦C. The observed fines concentration and increase in Ca2+ion production are found to be lower than with NaCl brine, which is attributed to ion exchange between Na+and Ca2+with NaCl brine. Temperature affects both (1) permeability increase due to pore enlargement caused by mineral reactions, and (2) permeability decrease due to fines migration.