Supercritical CO2 fracking for enhanced shale gas recovery and CO2 sequestration: Results, status and future challenges

Supercritical carbon dioxide (ScCO2)-based fracturing technology associating with CO2 enhanced shale gas recovery is a promising technology to reduce the water consumption and could provide the potential for CO2 sequestration. Advancing the understanding of complex gas shale reservoir behavior in the presence of multiphase and multicomponent gases (ScCO2, gaseous CO2 and CH4 etc.) via laboratory experiments, theoretical model development and field validation studies is very important. In this paper, the progress of some key scientific problems such as the mechanism of ScCO2 drilling and completion, the ScCO2 fracturing technology, the competition adsorption behaviors of CO2 /CH4 in shale, the coupled multiphase and multicomponent CO2 /CH4 flow during the CO2 enhanced shale gas recovery process and the CO2 sequestration potential in shale formation were discussed. The results indicated that the ScCO2 jet has a stronger rock erosion ability and requires much lower threshold pressure than water jet. The fracture initiation pressure of ScCO2 is about 50% lower than that of hydraulic fracturing, and the volume of rock fractured by ScCO2 is several times larger than that of hydraulic fracturing. Field test shown that the shale gas production rate was significant increased by the ScCO2-based fracturing technology. Finally, the challenges of the technique will face and the further research is needed in the future is exposed. © The Author(s) 2019.