Integrated Geology and Geomechanics Modeling for Deep Coalbed Methane Reservoirs: Challenges, Strategies, and Novel Solutions

ABSTRACT: This study presents a geomechanically-informed hydraulic fracture modeling workflow applied to two horizontal wells in a deep coalbed methane (CBM) pad. Key rock mechanical properties, including Young's Modulus, Poisson's Ratio, and in-situ stresses, were incorporated into the hydraulic fracture model to capture reservoir heterogeneity. A 3D Discrete Fracture Network (DFN) was integrated to account for natural fractures. The model was calibrated using observed pumping pressures, with adjustments to perforation parameters to match the simulated values. The calibrated hydraulic fracture geometry for Well-1 showed a half-length of 120.39 m and a height of 12.40 m, while Well-2 exhibited a half-length of 137.11 m and a height of 13.24 m. The effective fracture lengths were reduced to 95.10 m and 108.32 m, respectively, due to production-induced stress and proppant embedment. The Embedded Discrete Fracture Model (EDFM) was used to couple the fracture model with the reservoir simulation for long-term production forecasts. Estimated Ultimate Recovery (EUR) over a 20-year period was predicted to be 3.75 × 107 m3 for Well-1 and 5.16 × 107 m3 for Well-2. Drained Rock Volume (DRV) analysis provided insights into reservoir depletion and optimized well spacing strategies. 1. INTRODUCTION China's deep coalbed methane (CBM) reserves represent a substantial energy resource with significant potential to meet the country's growing demand for clean energy. As of 2023, annual CBM production reached 11.7 billion cubic meters, highlighting the resource's importance in the national energy mix. Recent exploration breakthroughs in the East Erdos Basin have revealed the vast untapped potential of deep CBM reservoirs, positioning this unconventional resource for accelerated development (Ma et al., 2024; Jia et al., 2024). However, deep CBM reservoirs differ markedly from conventional shale or tight gas reservoirs, posing unique geological and geomechanical challenges (Liu et al., 2024). These differences necessitate the use of specialized hydraulic fracture simulation techniques to optimize production strategies and address the complexities inherent in these reservoirs (Wang et al., 2024).