CBM Reservoir Characteristics And The Pattern Of Gas Accumulation In The Badaowan Formation Of The Southern Junggar Basin,northwest China

This paper is based on the study of coal bed gas geology in the Southern Junggar Basin.More than ten coal mines and some coalbed methane(CBM)well were reached to collect the coal samples.Many kinds of experiments were carried out,such as coal quality analysis,maceral analysis,scanning electron microscopy(SEM),isothermal adsorption experiment,mercury injection experiment and liquid nitrogen absorption/desorption experiment.Combining the geological data with CBM well logging data and test data,the physical and gas characteristics of CBM reservoir and their control mechanism are analyzed.The main results are as follows:(1)The CBM geological characteristics in the area are clarified through researching tectonic geological feature,stratigraphic sedimentation characteristics,hydrogeological feature and distribution characteristics of coal reservoir.(2)The effect of pore morphology and structural characteristics on permeability was studied by SEM,mercury injection experiment and liquid nitrogen absorption/desorption experiments.The pore radius distribution and morphological characteristics of seepage pores and adsorption pores are revealed through the fractal analyzing.With the damage degree of coal structure increasing,the specific surface area,pore volume and fractal dimension all show increasing trend,the pore structure complexity increases.(3)The numerical simulation of buried evolution,thermal history and hydrocarbon generation history are carried out.It established the forming and evolution model of coal reservoir,and revealed the control mechanism of physical property and gas property during reservoir forming and evolution.(4)Various gas content prediction models are compared,such as the Kim method,the Langmuir adsorption method and geophysical logging methods.The measured gas content data were used for inversion and verification,a gas content prediction model which is suitable for this study area is constructed and optimized.(5)The gas bearing characteristic,enrichment rules and main controlling factors of hydrocarbon accumulation in CBM reservoir are analyzed systematically.The integrated gas accumulation model of CBM in the Southern Junggar Basin is constructed under the control of multiple factors such as tectonic conditions,buried depth and roof lithology of coal seam.The most important controlling factors of CBM enrichment are folds and faults.The gas content of the Southern Junggar Basin is in the order of syncline > surrounding reverse fault > slope of syncline > slope of anticline > central of reverse fault,if only geological structure features are considered.