A Study on Phase State Characteristics During Multi-cycle Injection in the Collaborative Construction of Underground Gas Storage with Nanpu 1-5 Weak Volatile Reservoir

doi:10.11885/j.issn.1674-5086.2025.12.23.01

Abstract

Abstract: 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 reservoirs. 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.

Key words: weak volatile reservoir, collaborative gas storage construction, phase characteristics, multi-cycles of injection-production, EOR

CLC Number:

TE972

GAO Guangliang, MA Xiaoli, GU Xiao, JIANG Mingjie, LI Dan, LI Chun. A Study on Phase State Characteristics During Multi-cycle Injection in the Collaborative Construction of Underground Gas Storage with Nanpu 1-5 Weak Volatile Reservoir[J]. Journal of Southwest Petroleum University(Science & Technology Edition), 2026, 48(4): 71-80.

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