Quantitative Study of Oil Saturation Rebalancing for Horizontal Wells Production Enhancement- A Case Study from China

Abstract

To During the development and construction of a gas storage facility, the in-situ stress state of the reservoir undergoes dynamic cyclic variations due to natural gas injection and condensate production. Gas injection increases pore pressure within fractures, which may activate natural fractures or induce fault slip, thereby jeopardizing wellbore integrity and disrupting the secondary equilibrium of internal reservoir fluids. Four-dimensional geomechanical simulation can predict the stress distribution and evolution in the near-wellbore region. These simulation results can be applied as environmental loads to a three-dimensional static mechanical model, thereby enhancing gas storage safety and single-well deliverability. This study establishes a multi-porosity model incorporating matrix, natural fractures, and hydraulic fractures. Taking the YH Gas Storage facility in the Tarim Basin as the research subject, a numerical simulation approach is employed to optimize key production parameters, including total gas volume, gas injection rate, number of injection wells, and development cycles. A multi-parameter optimization methodology combining single-variable and multi-variable analyses is adopted. Subsequently, a four-dimensional geomechanical model accounting for faults and fractures is developed to investigate the temporal evolution of in-situ stress and rock displacement under the optimal gas injection scheme. Finally, based on finite element theory, a finite element model of the wellbore-reservoir-fault assembly is constructed. The results indicate that while the gas injection capacity of the 13 optimized wells is sufficient relative to the preliminary design of 17 injection/production wells, their gas production capacity carries certain risks. It is recommended that these 13 wells operate for 2–3 injection/production cycles to conduct an in-depth evaluation of capacity attainment. Should the 13 wells prove insufficient for production targets, two mitigation strategies are proposed: utilizing existing wells for production or drilling the four reserved infill wells. The designed daily peak-shaving capacity is 20.0×106m3/d with a working gas volume of 24.0×108m3 per year. The operating pressure range is 36.4-44.7 MPa, with an upper limit of 44.7 MPa. This study provides technical support for the long-term safe and stable operation of the YH Gas Storage facility and the high-deliverability development plan for horizontal wells.