Effect of type of ion and temperature on fines migration induced by mineral reactions during water injection into carbonate rocks

Abstract

Managed aquifer recharge is a water storage and recovery method. However, fines migration during water injection can significantly affect formation permeability. Several studies have analyzed fines migration in sandstone and soil samples, but few studies have investigated fines migration in carbonate rocks. In addition, the effect of neither temperature nor type of ion on fines migration has been investigated in carbonate rocks.Our experiments use filtered-deaired distilled water and pure salts to prepare the injection fluids. Rock samples are injected with 0.63 mol/L brine followed by four sequential injections of diluted brine: 0.21 mol/L, 0.1 mol/L, 0.05 mol/L, and 0 mol/L (distilled water). Pressure difference is recorded across the rock sample throughout each experimental run and used to calculate permeability. Effluent is collected to characterize produced fines and elements. pH and particle concentration measurements are collected frequently. Scanning electron microscope (SEM) images of inlet and outlet faces pre- and post-injection were taken to observe any changes.For the experimental runs performed at 25 °C, permeability decrease was 99.92% of the original permeability for seawater experimental run, 99.96% for NaCl brine experimental run, and nearly zero for CaCl2 brine experimental run. For CaCl2 brine experimental run, the only observed mineral reaction is mineral dissolution. For NaCl brine and seawater experimental runs, both mineral dissolution and cation exchange are observed, of which the latter appears to be the main mechanism for fines migration. Due to mineral dissolution, permeability increase is observed during 0.21 mol/L and 0.1 mol/L injection at high temperature. However, during distilled water injection, permeability decrease is found to be similar at both low and high temperatures.