A discussion on analytical and numerical modelling of the land subsidence induced by coal seam gas extraction

Abstract

Coal seam gas (CSG) is an increasingly important source of natural gas all over the world. Although the influence of conventional oil and gas extraction on surface subsidence has been widely recognized and studied, few studies are carried out on the surface subsidence in coal seam gas fields and its impact on surface infrastructure and the environment. This paper discusses modelling of the surface subsidence associated with coal seam gas production by applying both analytical and numerical methods. By comparison of results from the numerical model and two analytical models, i.e. the disc-shaped reservoir model and the uniaxial compaction model, the analytical solutions cannot describe the complex process of water and gas extraction and have the limitations to predict the surface subsidence, while the numerical model can be better used in prediction of subsidence. After applying the numerical model in numerical analysis, the deformation characteristics of coupled fluid flow, and the effects of permeability change of coal seam, associated overlying and underlying layers, and depressurization rates on surface subsidence are investigated. The results demonstrate that the proposed model can simulate the production of water and gas from coal seams and the associated surface subsidence.