Prediction of CBM sweet spots via matching trace decomposition-based fluid activity factor

The exploration and development of CBM is one of the hotspots in the exploration of unconventional oil and gas resources in China, and a lot of breakthrough on CBM exploration and development have been made in recent years. However, it is difficult to identify CBM with strong coal seam heterogeneity and adsorption state, and it is of great importance to use the lateral advantage of seismic data to predict the sweet spots of CBM reservoirs in case of scarce drilling data and insuffisant use of post-stack seismic data. Conventional post-stack seismic inversion method can identify the coal seams, but cannot predict the gas-bearing property of coal seams. However, the fluid activity factor based on seismic attenuation theory can effectively characterize the permeability of the reservoir and recognize the gas-bearing coal. In this paper, we propose to use the fluid activity as a sign of hydrocarbon content. First, the matching pursuit method was applied for seismic wavefield separation. Then, the fluid activity factor was calculated after building the relationship between the gas-bearing coal and seismic attenuation. Based on the above steps, we can obtain the high-precision distribution of CBM sweet spots. This method is faithful to seismic data and can be applied without the limitations of structural and sequential interpretation, thus can objectively reflect the gas-bearing situation. Theoretic model test and the application of coalbed gas exploration in Qinshui basin prove the effectiveness and feasibility of the proposed method.