Current research into the use of supercritical CO2 technology in shale gas exploitation

The use of supercritical CO2 for shale gas extraction is a promising new technology. This paper explores current research into this process, looking at analysis of the mechanism of CH4 displacement in nanoporous shale, the positive and negative effects accompanying its use for sequestration as well as organic extraction, the migration of elements and the swelling process, and the macro and micro control mechanisms involved in permeability enhancement in reservoirs. Fruitful directions for future research are also considered through comparison with hydraulic fracturing. The research findings indicate that ScCO2 fluid replacement can be used to increase gas production and seal up greenhouse gases as an effective, clean and safe method of shale gas exploitation. It is particularly effective for promoting the desorption of CH4 in shale reservoirs that have developed fine neck-wide body pores, and the subtle structural changes effected by ScCO2 fluid in sensitive minerals in reservoirs with a high brittle mineral content also have a positive effect on permeability and storage capacity. The adsorption process has been characterized as consisting of three stages: short-term shrinkage, slow swelling, and stability; an expansion equation has been proposed for CO2/CH4 that incorporates competitive adsorption, collision desorption, and impingement re-adsorption. ScCO2 fracturing has been found to be more effective than hydraulic fracturing for dense reservoirs and more effective at linking up pore-micro-fissure-fracture systems. (C) 2019 Published by Elsevier B.V. on behalf of China University of Mining & Technology.