Experimental Investigation of the Geochemical Interactions between Supercritical CO₂ and Shale: Implications for CO₂ Storage in Gas-Bearing Shale Formations

Abstract

Interactions between injected CO2 and shale formation during the process of CO2 sequestration with enhancing shale gas recovery (CS-EGR) may alter the physical and chemical properties of the rock, affecting the efficiency of CO2 storage as well as CH4 production. To better understand these interaction-induced changes in shale properties, two shale samples selected from a marine Longmaxi formation and terrestrial Chang-7 member of the Yanchang formation were first reacted with supercritical CO2 (scCO2) in a laboratory batch reactor at 80 °C and 15 MPa with different time intervals, and then characterization methods were designed to access the geochemical changes including optical microscope (OM), X-ray diffraction (XRD), element analysis (EA), low-pressure gas adsorption (LPGA), and Fourier transform infrared spectroscopy (FTIR). The results indicate that the nanopore structure system of the two shale samples was significantly changed after scCO2–shale interaction due to the scCO2-induced extraction of hydrocarbons, chemical reactions in minerals, and the swelling effect in clay minerals as well as organic matter. However, after exposure to scCO2, the variation trend of pore structure parameters between the marine Longmaxi and terrestrial Chang-7 sample was quite different, which was related to the huge discrepancies in terms of mineralogy and geochemical properties between them. For marine Longmaxi sample, the pore surface area and pore volume obviously decreased after a relatively short period of scCO2 treatment, whereas an opposite trend was observed in a terrestrial Chang-7 sample after long-term scCO2 treatment. In addition, an obvious decrease in fractal dimensions for marine Longmaxi sample was also observed after scCO2 exposure, reflecting the degree of pore surface roughness, and pore structure complexity were reduced, whereas the terrestrial Chang-7 sample exhibited an opposite trend. The results contribute to the understanding of the potential factors for the pore-structure evolution during long-term CO2 storage and the possible effect on the CS-EGR process.

A review of CO2 storage in geological formations emphasizing modeling, monitoring and capacity estimation approaches

“…These equations (Eqs. 10, 11 and 13) represent the fundamental equations for the modeling of storage of CO 2 in porous media (DePaolo et al 2019;Nghiem et al 2004;Pan et al 2018a). These equations could be coupled with geochemical reactions, geomechanical modules and other relevant physical phenomena.…”

A Review on the Influence of CO2/Shale Interaction on Shale Properties: Implications of CCS in Shales

“…In the long-term, formation brine will dissolve the injected CO 2 and causes reactions with the shale rock, leading to mineral precipitation and dissolution which may affect the shale storage capacity [1,38]. The CO 2 /shale interaction is a key factor for the efficiency of CCS in shale formations; it can significantly alter the shale properties, which in return affect the rock geometry, fluid transportation, and storage capacity [39,40]. The presence of organic and inorganic components in a heterogeneous porous medium such as shale permits the injected CO 2 to interact with clay minerals and organic matter through chemical dissolution [39].…”

A Review of Gas Injection in Shale Reservoirs: Enhanced Oil/Gas Recovery Approaches and Greenhouse Gas Control

“…Gas adsorption-or desorption-induced swelling or shrinkage of shale can affect the pore structure and have an impact on gas transport in shale [74,75]. Recently, many studies focused on the change of physio-chemical properties of shale due to carbon dioxide (or other gases) injection.…”

“…Recently, many studies focused on the change of physio-chemical properties of shale due to carbon dioxide (or other gases) injection. The adsorption capacities of different gases [74][75][76][77][78], adsorption-induced swelling strain and swelling rate [77,79,80], gas diffusion in shale [76,81], and physical and chemical structure change [82] have been investigated in different studies.…”