Variation of pore-network, mechanical and hydrological characteristics of sandstone specimens through CO2-enriched brine injection

The main goal of this study was to capture the variations in pore-network, mechanical and hydrological characteristics of two different sandstone specimens subjected to CO2-enriched brine injection. The first sandstone specimen (S1) was from Allegheny National Forest, Northwestern Pennsylvania and the second one was a Triassic Pecos sandstone (S2) from Barstow (TX) quarry. Core-flooding experiments were performed under different overburden stresses and pore pressure conditions to determine the permeability of sandstone specimens to brine and CO2 -enriched brine. Subsequently, variations in porosity, pore-size distribution and surface gas permeability were evaluated. In addition, changes in mechanical characteristics of the specimens were investigated through isotropic compression, multi-stage elastic, and cyclic tests. Evaluation of the permeability evolution revealed significant permeability enhancement during CO2-enriched brine injection, where the S2 specimen's permeability was increased up to 3 times and permeability of S1 increased by two orders of magnitude. The porosity of S1 and S2 specimens increased by 3.60% and 2.87% and the pore connectivity enhanced by 72.1% and 23.2%, respectively. Furthermore, following CO2-enriched brine injection, the average surface gas permeability of S1 and S2 specimens increased by similar to 12.6 and similar to 4.5 times, respectively. In addition, we observed that the mechanical weakening in both specimens caused by mineral dissolution. More specifically, during the CP of 40 MPa, the average Young's modulus decreased by 31.3% and 15.3% for S1 and S2 specimens, respectively. Also, the average bulk modulus of S1 and S2 specimens decreased by 26.8% and 22.7%, respectively. On the other hand, increasing the expansion tendency was reflected in increasing the Poisson's ratio, where the average Poisson's ratio increased by 19.5% and 25.3% for S1 and S2 specimens, respectively. However, conducting additional experiments on sandstones with various mineralogies are required to confirm the repeatability and statistical significance of the obtained results. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This study investigated the variations in pore-network, mechanical, and hydrological characteristics of two different sandstone specimens subjected to CO2-enriched brine injection. The results showed significant permeability enhancement, increased porosity, enhanced pore connectivity, and increased surface gas permeability during CO2-enriched brine injection. Additionally, changes in mechanical characteristics of the specimens were observed, with mineral dissolution causing mechanical weakening in both specimens. Conducting further experiments on sandstones with different mineralogies is necessary to confirm the repeatability and statistical significance of the obtained results.