Coalbed methane gas content and its geological controls: Research based on seismic-geological integrated method

Abstract

Gas content is a crucial indicator in the process of coalbed methane (CBM) exploration and development. However, the strong heterogeneity of CBM reservoirs makes it difficult to predict gas content by conventional geological methods. In this paper, we proposed a seismic-geological integrated method that is based on main controlling factors to predict coalbed gas content. The first step is to construct parameters such as deformation residual, fault density, net-to-gross ratio, and coal thickness to quantitatively analyze the effect of geological factors on gas content. Results show that tectonic deformation, fault systems, burial depth, and the sandstone content of the sequence after coal accumulation are key factors controlling the gas content, whereas coal thickness is weakly correlated with the gas content. Then, the degree of tectonic deformation and displacement were quantitatively calculated on the basis of 3D seismic interpretation, and the spatial distribution of sedimentary bodies and coal thickness was acquired by seismic sedimentology and facies-controlled inversion. Finally, a weighted fusion method was proposed to construct a multivariate linear model to quantitatively predict the gas content. The relative error of gas content predicted by the integrated method is 10.2%–28.4%, indicating that this new method is applicable and feasible. In addition, according to the combination of gas controlling factors, the CBM enrichment scenarios in the study area were divided into three types, in which the deep-buried, local concave, muddy roof regions are most favorable for CBM accumulation (Type Ⅲ, located in the southeast and north parts of the study area). This study provides a new way for block-scale CBM enrichment prediction under complex geological conditions.