纹层页岩CO2复合压裂裂缝特征及穿层扩展规律OA

To investigate the fracture characteristics and layer-crossing propagation law of CO2-hybrid fracturing in laminated shale,CO2-hybrid fracturing experiments were conducted with the full-diameter Jiyang Sag Shale,and the Cohesive unit model was used to simulate the effect of pre-CO2 injection rate on layer-crossing propagation.The results show that:1)CO2 fracturing is easy to activate beddings and natural fractures,which provides conditions for the formation of complex cross fractures in subsequent hydraulic fracturing,and the fracture volume increased by 24.0%with doubled pre-CO2 injection rate;2)The low viscosity and high permeability of CO2 easily induce fractures to propagate along weak surfaces(beddings,natural fractures),mineral grain boundaries,and pore directions,resulting in the roughness of CO2 fracturing fractures about 50.0%higher than hydraulic fractures;3)With the increase of CO2 injection rate,the ability of fracture to pass through beddings is enhanced.At low CO2 injection rate,fracture propagation is dominated by bedding,while fracture propagation is dominated by in-situ stress at high injection rate.The research results provide the mechanism and theoretical understanding of the fracture propagation law of CO2-hybrid fracturing of shale oil reservoir in Jiyang Sag.Compared with conventional fracturing in the field,the stimulation volume of CO2-hybrid fracturing increased by 12.2%,capacity by 33%,and decline rate of oil production decreased by 6.8%.