Research On Methods Of Anti-channeling Of CO₂-flooding In Low-permeability Reservoirs

For low-permeability reservoirs with difficult water injection,CO₂ development is an effective method.CO₂ can reduce oil viscosity,expanse oil volμme,diffuse and reduce interfacial tension.If the reservoir pressure and temperature are high enough,the miscible flooding will be achieved.CO₂ flooding technology is applied to low-permeability fractured reservoirs,cracks are the main controlling factors,so it is necessary to conduct profile control and plugging.We studied the microsphere swelling ability and pressure resistance.The microsphere swelling experiment shows that the large-scale microsphere has the best swelling ability,followed by the micro-scale microspheres,and the nano-scale microspheres were the worst.The experimental results of microsphere pressure resistance show that the nano-scale microspheres have the best pressure-resistance performance,micron-scale microspheres are the second,and large-scale microspheres are the worst.We used the artificial fracture core as model to simulate the reservoir environment,the combined microspheres and gel foam as the deep profile control agent.The plugging experiment was used to determine the adaptability of different concentrations and different sizes of microspheres for different core permeability and different width of fracture.By the oil displacement experiment,it can be determined that CO₂ can expand the sweep efficiency.The plugging experiments show that the nano-sized microspheres are suitable for the width than 15μm,the micro-scale microspheres are suitable for for the width between 17.0-22.75μm,and the large-scale microspheres are suitable for the width between 22.75-50.09μm.Oil displacement experiments show that the secondary gas drive can increase the recovery rate of 22.5%-27%after injecting the microsphere.For wider cracks,a foam gel plugging agent was tried when the microsphere system was no longer suitable as a profile control agent.We studied the foam volμme,viscosity,half-life,plugging ability and oil displacement ability of the gel foam.The results show the foam volμme of the gel foam is 670 mL,the viscosity is 46254 mPa·s at 80℃,and the half-life at 80℃is 12 days.The gel foam plugging capacity is suitable for width of fracture more than 50μm,and the development of secondary CO₂ injection after plugging can increase oil recovery by 28%.