Study On Formulation And Evaluation Of Temperature And Salt Resistant System For CO₂ Flooding Mobility Control

For the gas channeling flow of CO₂ flooding reservoirs,many methods have been proposed to control CO₂ mobility process at home and abroad:the water-alternating-gas（WAG）process,CO₂ viscosifier,CO₂ foams and cross-linked gel.The cross-linked gel was used as research object.Cross-linked polymer solutions were injected into the ground,then it can effectively block CO₂ gas channeling after high-temperature gelation.Polyacrylamide gel system was used to develop the SDC-1 CO₂ mobility control system which optimized MK-type organic-inorganic compound crosslinker.The optimal formulation was determined to be 1%polyacrylamide+2%K-type crosslinker+0.2%M-type crosslinker+0.1%thiourea.The influence factors,viscoelasticity and micro-morphology of the system were studied by means of visual code method,rheometer measurement,environmental scanning electron microscopy,spectral analysis and displacement test.The results show that a large number of spherical and branch structures can be formed by the combined use of M-type and K-type cross-linking agents.It can effectively improve the temperature and salt resistance of SDC-1 system which can endure 90 days,also the gelation time is 12 h under 115℃,2×10⁴ mg/L.The storage modulus G′of the system is mainly affected by the addition amount of the M-type crosslinking agent.Nano-SiO₂ is mainly adsorbed on the branch structure of the system,thereby enhancing the strength of the gel system.SDC-1 control CO₂ mobility system has good injectability:base fluid viscosity retention rate after shearing reaches 80.5%and can form strong gel.Breakthrough pressure gradient up to 12.3 MPa/m,and the blocking rate up to 95.67%after long-term erosion of CO₂.SDC-1 system has good temperature and salt resistance and plugging effect.It can be applied to CO₂ gas flooding reservoirs to prevent gas stagnation problems.