Chemo-Mechanical Alterations During Geologic Carbon Sequestration in Sandstone: Experimental Observations

Abstract

CO 2 injectivity and storage capacity in sandstone may be impacted by fluid-rock interaction and resultant compaction during carbon sequestration. Although chemical, mineralogical and petrophysical changes are well characterized during fluid-rock interaction in CO 2 -rich systems, the coupling of CO 2 -driven alteration of sandstone with mechanical property changes is less known. Six flow-through experiments were conducted on Pennsylvanian Morrow B Sandstone cores from the Farnsworth Unit in West Texas, USA. CO 2 -rich brine flowed through core samples of poikilotopic calcite-and disseminated ankerite-siderite-cemented sandstone at flow rates that ranged from 0.01 to 0.1 ml/min at 71°C and 29.0 MPa pore fluid pressure. Fluid sample analysis performed by ICP-OES from experiments on both carbonate-cemented sandstones indicate that carbonate cement dissolution is likely the dominant chemical process. The permeability of the ankerite-siderite-cemented sandstone changed little from the reaction with carbonic acid, whereas the permeability of the calcite-cemented sandstone significantly increased by more than one order of magnitude (from 3.3×10 -18 to 7.8×10 -17 m 2 ). P-and S-wave velocities measured from pre-and post-experiment ultrasonic tests were used to estimate the changes in dynamic Young's and shear moduli. Furthermore, cylinder-splitting tests were conducted to measure the tensile strength of the altered post-experimental samples and compared to the control samples that only interacted with pure brine. All samples underwent slight decreases in Young's and shear moduli, and the cylinder-splitting tests suggest that mechanical degradation may be concentrated on the upstream end of the calcite-cemented sample. Our findings help in predicting chemo-mechanical changes at carbon sequestration sites where the reservoir lithology is carbonate-cemented sandstone.