Coalbed Methane (CBM) Reservoir Characteristics And Control Mechanism In Weibei Area

Weibei area in the southeastern margin of the Ordos Basin, is one of the two coalbed methane(CBM) zones which have achieved large-scale commercial development. However, the forming conditions of the coal reservoir are very complex, while the structural conditions are even more complex, since this area locates on the edge of the basin. As a result, the reservoir has strong heterogeneity, which has brought great difficulties to CBM development in this area. In this thesis, Weibei CBM-rich region is considered as the study area, where geological research work were carried out from coal mining areas in Hancheng, Heyang and Chengcheng. Coal and rock samples were collected from more than 20 coal mines, which were used for kinds of tests and experiments, such as coal properties, coal composition, micro fractures, scanning electron microscope(SEM), isothermal gas adsorption, mercury porosimetry, porosity, permeability, X-ray CT scanning, and acoustic emission, etc. Based on geological data and CBM well testing data, CBM reservoir characteristics and control mechanisms in Weibei area were analyzed, which details are as follows:(1) Based on systematic study on characteristics of tectonic, sedimentology, hydrogeology, development and distribution of coal reservoir, geological characteristics of CBM-rich region in Weibei area are clarified. Geological control mechanisms of differential development of coal reservoirs are portrayed.(2) It reveals the CBM reservoir characteristics and geological control factors in Weibei area, through analysis on the characteristics of gas content, adsorption and desorption, fracture development, well logging response of CBM reservoir. A quantitative well logging model of reservoir properties is established.(3) The forming and evolution model of CBM reservoir is established, based on numerical simulations of burial history, thermal evolution history and hydrocarbon evolution history. It shows the forming and evolution characteristics of CBM reservoir, and its control mechanism on physical properties of coal reservoir.(4) Gas adsorption and desorption characteristics of coal reservoir under different temperatures are studied, by applying isothermal adsorption experiments under different temperatures. A comprehensive adsorption model under different temperatures and pressures of coal reservoir is established.(5) The control mechanisms of gas slippage, matrix shrinkage and effective stress effects on evolution of cracks and permeability of coal reservoir are demonstrated, based on coal permeability evolution experiments under different pressures. The models of coal permeability evolution under different pressures are established.