In-situ fines migration and grains redistribution induced by mineral reactions – Implications for clogging during water injection in carbonate aquifers

Abstract

Water injection into an aquifer is generally motivated by one of three objectives: disposal, managed aquifer recharge (MAR), or aquifer storage and recovery (ASR). Any of these would be undermined if an injection well were to become clogged. This paper investigates whether mineral reactions can cause mobilization of fines and rock grains, and if so, how this would affect clogging. Injection experiments are performed on Edwards Brown (dolomite) and Indiana limestone core samples. X-ray Powder Diffraction analysis of the rocks shows that no clays are present. Filtered-deaired deionized water and pure salts are used to prepare the injection fluids. The core samples are subjected to four sequential injections of fluids: at salinities 44,580 mg/L (referred to as “seawater”), 14,860 mg/L, 7,430 mg/L, and 0 mg/L (deionized water). These salinities are selected to represent disposal, and less saline fluids to represent MAR and ASR projects. Pressure difference is recorded across the core sample at each stage and is used to calculate permeability. The effluent samples are collected to characterize produced fines and elements. The increase in the pH of the effluent samples suggest mineral reactions, which is supported by an increase in the concentration of chemical elements in the effluent samples. Scanning Electron Microscopy (SEM) images show pore enlargement due to dissolution and depict pore blockage due to fines migration, grains redistribution, and mineral precipitation. Mineral reactions dissolved the grain's surface and intergranular cement, releasing silicate fines and rock grains, which in turn reduce the permeability of the rock by 68 % to 99.9 %.