Evaluation of Closely Spaced Infill Wells in Unconventional Mature Coalbed Methane Field: A Simulation Approach

This study presents the work carried out to evaluate the effectiveness of closely spaced infill wells in enhancing recovery from a mature coal bed methane (CBM) field. The primary objective was to assess the potential for increasing gas production rates, accelerating reserve monetization, and improving the overall recovery efficiency in an unconventional reservoir setting. The authors utilized an integrated approach combining core-hole data, geological and geophysical models, historical production performance, and a history-matched dynamic reservoir model to support technical decisions. A finely gridded cellular model was developed for numerical simulation, enabling detailed history matching over the entire production period. This allowed for a reliable evaluation of the infill well impact on reservoir dynamics and the remaining reserves of offset wells originally developed with wider well spacing. The study was applied to a distinct area within a mature CBM field, using data sets available in the public domain. Simulation results showed a strong correlation with the actual pilot infill well performance, validating the methodology. Quantitative outcomes demonstrated the tangible benefits of the infill strategy: a 30% plus increase in peak field gas rate, a 12% plus gain in recovery factor, a 2-fold acceleration in average reservoir pressure depletion, and a 1.5 to 2 times faster recovery of project capital expenditure. These improvements directly translate to more efficient resource utilization and better project economics. The work demonstrates how the application of a simulation-based approach combined with real field data can guide infill drilling strategies in unconventional CBM reservoirs. It offers a technically robust, cost-effective method to optimize late-life field development, while adhering to sound reservoir management principles.