南堡1-5弱挥发性油藏协同建库多轮次注采相态特征研究OA

Compared with conventional underground gas storage construction in depleted gas reservoirs,fluid compositional migration and phase behavior changes are more complex during multi-cycle injection-production in weakly volatile oil reser-voirs.To reveal the phase-equilibrium evolution during cyclic injection-production,this study takes the Nanpu 1-5 weakly volatile oil reservoir as the target and establishes a phase-equilibrium experimental procedure and theoretical simulation model for multi-cycle injection-production.The variations in the composition,phase behavior,saturation,and recovery degree of produced and residual fluids were investigated.The results show that after five injection-production cycles,the oil saturation decreased by 2.4%,which is conducive to increasing gas storage space.The methane content of the produced gas increased from 93.8%to 95.3%,while CO2 and C2+components gradually decreased,indicating a weakening extraction effect of the injected gas.The C7+mole fraction of the residual oil increased by 9.2%;under the upper and lower pressure limits,the solution gas-oil ratio decreased from 185 and 88 m3/m3 to 78 and 35 m3/m3,respectively,and the oil formation volume factor decreased from 1.57 and 1.32 to 1.24 and 1.16,respectively,indicating gradual heavy-end enrichment of the residual oil.This study clarifies the relationships among compositional migration,phase behavior evolution,and gas storage space expansion,providing a basis for optimizing cyclic injection-production strategies in similar oil-reservoir-based underground gas storage projects.