Radial heterogeneity evaluation of coalbed methane reservoirs and its application

Compared to conventional natural gas reservoirs, CBM(coalbed methane) reservoirs are susceptible to the multi-period tectonic effect that strengthens the heterogeneity of reservoirs and then influences the distribution of CBM, so it's difficult to predict the CBM productivity. First of all, in contrast to the NMR T2 spectrum, the porosity spectrum of micro-electric imaging logging could be successfully applied to study the micro-porosity distribution. Based on this, it is optimized to apply the Lorenz curve method to derive a variation coefficient to characterize the heterogeneity of the area by comparison of the advantages and disadvantages of the statistical method, Dykstra-Parsons empirical formula method and Lorenz curve method. According to the degree of heterogeneity and the internal structure features, the main productive layers can be divided into layer-block structure and block structure. Finally, the CBM content is evaluated in accordance with the structure classification, further providing reference for the productivity forecast.