A Review of Coupled Geo-Chemo-Mechanical Impacts of CO2-Shale Interaction on Enhanced Shale Gas Recovery

Abstract

Shale is an important geological media for carbon capture utilization and storage. On one hand it can be regarded as impermeable caprock to prevent CO2 migration from reservoir, and on the other hand it can be also treated as natural gas and CO2 storage reservoir. CO2-shale reactions within caprock can interfere the rock integrity so as to bring threatens to the long-term carbon storage safety and stability, however this interaction can also improve rock conductivity to enhance shale gas recovery for the organic-rich shale. This article presents a review of the current state of knowledge regarding CO2 and shale interactions and their potential impacts on shale properties and groundwater quality in the context of CO2 enhanced shale gas recovery. The characterization of gas shale and CO2, which is critical to the occurring of different interactions between CO2 and shale, is firstly summarized. The major interaction mechanisms between CO2 and shale including CO2-shale-water geochemical reactions, CO2 adsorption induced clay swelling and organic matter extraction with supercritical CO2 and their impact on rock porosity, permeability, mechanical properties, gas adsorption capacity and groundwater quality are surveyed. Finally, the open questions in the field are emphasized and new research needs are highlighted.