Key Controlling Factors Comparison Between High And Low Rank CBM Reservoir Formation

It was proved by CBM geological researches and exploration & development that there were some obviously differences between high and low rank CBM reservoirs, including geological characters, reservoir formation evolution and development techniques. Comparison about key controlling factors of high-low rank CBM reservoir formation not only is an essential part of the CBM formation mechanism, but also has the great theoretical and practical significances to development and improving Chinese CBM basal geological theory and effective developing CBM resources.Based on the Chinese CBM geological characters, the analysis and researches mainly focus on the Qinshui basin, the Ordos basin and the Junggar basin here. Through the comparison of the geological characters and formation evolution of high-low rank CBM reservoir formation by means of the large number of tests and physical simulations, the differences of the coal reservoir physical property between high and low rank and the different affection of CBM concentration and accumulation by the conservation conditions were analyzed and discussed. It was firstly confirmed that the different rank coals express the different desorption characters and desorption speed. The different affections controlled by the coal reservoir physical property and CBM conservation condition were creatively clarified and the CBM formation models were firstly summed and built.As a result, it was proved that the low rank coal had the relative higher phase desorption speed and larger percentage of the earlier desorption volume. Moreover, with the coal seams uplift and the reservoir pressure decreasing, the high rank coal reservoir physical property becomes better and the CBM dissipating volume largely increases because of the expanding coal block and the open cleat system. Additional, the flowed groundwater could damage the high rank CBM accumulation. Oppositely, the slightly flowed groundwater may provide the essential condition of methane bacteria living, which was important to the secondary biogas supply of the low rank CBM reservoir formation. At last, the built CBM reservoir models includes the basin syncline model, margin monocline model and anticline model, et.