Effects of CO2/Rock/Formation Brine Parameters on CO2 Injectivity for Sequestration

Abstract

Summary The injection of carbon dioxide (CO2) into saline aquifers is highlighted as an effective technique to permanently secure anthropogenic gas produced from high CO2 gas fields in the Southeast Asia region. However, previous studies indicate that CO2 injectivity can be impaired primarily due to the interactions between CO2/brine/rock. In this paper, we investigate the effect of a CO2 injection scheme, rock permeability, brine type, and salinity on CO2 injectivity, which is presented by permeability alteration. A CO2 coreflood experiment and the characterization of the rock and effluent produced are presented. Furthermore, core samples with different permeabilities of the typical geological storage for sequestration were selected and analyzed using X-ray fluorescence (XRF), X-ray diffraction (XRD), and field-emission scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (FESEM-EDX). The cores were then saturated with synthetic brine composed of 6,000, 30,000 or 100,000 parts per million (ppm) of either sodium chloride (NaCl), potassium chloride (KCl), or calcium chloride (CaCl2). Subsequently, the core samples were injected by either supercritical CO2 (scCO2), CO2-saturated brine, or CO2-saturated brine followed by scCO2. The fines particles from the collected effluent were separated for further analysis. The results indicate that a CO2 injection scheme, injection flow rate, brine salinity, and initial rock permeability are the principal factors that contribute to the permeability alteration of the core samples. It was also found from FESEM-EDX analysis of the produced fines that the precipitated salt, silica grains, and kaolinite migrated during scCO2 injection, suggesting the dissolution and precipitation of minerals. This phenomenon led to the migration of particles, some of which plugged the pore spaces and reduced the permeability. Besides, the core saturated with CaCl2 brine was the only sample with improvement in permeability after the CO2 flooding experiment.