Energy mechanism of gas channeling channels in complex fracture networks for CO2 injection in ultra-low permeability reservoirs

The injection of CO2 into ultra-low permeability can enhance production as well as accomplish storage of carbon. However, the gas channeling phenomenon is serious and there is a lack of explanation of the energy mechanism. Based on the current state of CO2 gas channeling in the Y29-105 well group located in the Huang 3 block of Jiyuan Oilfield, this study utilises the ABAQUS finite element cohesion model to explore the mechanical evolution of the CO2 channel expansion process. And according to the size of the cross-flow channel, intra-fracture pressure, damage displacement and expansion pressure, it is divided into the unconnected stage, the inter-well connected stage and the well group connected stage. Furthermore, we also established energy judgment criteria for the expansion behaviour of gas channeling channels, including stopping at natural fractures, extending along natural fractures, and directly crossing natural fractures. Upon comparison with theoretical and experimental results, it was determined that the energy discrimination criterion is appropriate for expansion along natural fractures and cross natural fractures. It can be seen that our research results can offer energy mechanism support for preventing, controlling, and predicting large-scale CO2 injection in ultra-low permeability reservoirs.