Research and application of the prediction method for CBM enrichment area of low rank coal

The exploration of low rank coal coalbed methane(CBM) faces the problems of low resource exploration rate and low single well production. And medium and low rank coal CBM exploration is still in the primary stage. In order to improve the predition accuracy of the low rank coal CBM enrichment area, the laboratory test data of 652 coal samples from 56 wells in Hancheng, Jincheng Baode, Ji'ergalangtu Qinshui Basin, Huainan, Huaibei and other places were collected to compare the relationship between gas content and elastic parameters of high, medium and low rank coal samples. The results indicated that the correlation between coal seam gas content and elastic parameters of different coal rank is consistent. And density is more sensitive to the changes of gas content of low rank coal than that of medium and high rank coal. It is considered that low coal-rank CBM reservoirs have the basis for identification using geophysical methods. On this basis, the 3D seismic data of the Ji'ergalangtu depression was selected and the pre-stack elastic modulus parameter inversion method was applied to predict its coal-bed methane enrichment area in the Ⅳ coal group of the Lower Cretaceous Saihantala Formation with a total area of 101 km², which provides a high-quality construction area for the next development. The coincidence rate between the predicted results and gas content test results was 83.3%, which further proved that it was feasible to detect the low rank coal CBM enrichment area by prestack elastic parameters inversion of relative change. The research results have certain guiding significance for the exploration and development of low rank coal CBM.