A Coupled Hydro‐Mechanical Modeling Framework to Concurrently Simulate Coal Seam Gas Induced Subsidence and Groundwater Impacts

Land subsidence has been extensively studied and modeled in the context of conventional petroleum or water extraction. New challenges arise to model subsidence caused by coal seam gas (CSG) depressurization. CSG‐induced subsidence is a result of multiple interrelated hydro‐mechanical processes that involve poroelastic compaction, desorption‐induced shrinkage, and two‐phase flow. This study proposes an innovative modeling framework to integrate newly developed techniques with existing methods to simulate CSG‐induced subsidence. The primary components of the framework include: (a) implementation of a pseudo‐two‐phase formulation to simulate pressure changes from CSG extraction; (b) dual‐domain representation of coal measures for lithological upscaling; (c) hydro‐mechanical coupling to account for poroelastic compaction and coal shrinkage; and (d) data assimilation to integrate InSAR, water production and groundwater levels. The framework is demonstrated by applying it to a typical CSG field in Australia. The results provide new insights into the spatial/temporal evolution of subsidence within CSG fields. Throughout the life of the case‐study CSG field, the maximum subsidence at well locations can vary from 45 to 235 mm, with a mean of about 110 mm depending on the hydro‐mechanical properties of coals and interburden. The subsidence during life cycles of CSG development can be divided into three stages including a growing stage, a stabilized stage and a recovery stage. The subsidence rate generally decreases exponentially until the maximum subsidence is reached. The proposed framework allows efficient modeling of CSG‐induced subsidence across local to regional scales, laying a foundation for subsequent farm‐scale assessment of the agro‐economic consequences of CSG‐induced subsidence.