The Study Of Coalbed Methane Enrichment Rule And Productivity Analysis Of CBM Wells In The Tunlan Domain,Xishan Coalfield

This paper is based on the CBM geology and fracturing drainage data of Tunlan domain in the Gujiao area,Xishan coalfield,the identification of coal macerals,vitrinite reflectance,gas content,water chemistry detection,dynamic porosity and permeability,dynamic acoustic wave velocity,low-field NMR properties,and other test analysis of 17 coal block samples and 16 water samples collected from 16 coalbed methane wells,which were collected from the Nos.2 and 8 coal seams in the research area,were measured.Based on the basic geological exploration data and test results,the geological structure,sedimentary environment,hydrogeology,and physical properties of coal reservoirs in the Tunlan domain were studied,and the dominant factors that influence the richly integrated reservoir of CBM in the research area were basically clarified.Based on the study of the CBM enrichment rule and the quantitative evaluation of coal reservoirs,according to the data of coalbed methane wells,the principal elements affecting the production capacity of CBM wells were analyzed in combination with the engineering measures and drainage system adopted in the construction and drainage of coalbed gas wells,which provides a scientific basis for the comprehensive evaluation of CBM and the adjustment of the CBM development plan in the next step.The main research results and recognition are as follows:（1）The effects of geological structure,sedimentary environment,and hydrogeology on the coalbed methane enrichment in the research area were comprehensively analyzed.Through the systematically analysis of the tectonic evolution history and the geological conditions of enrichment and accumulation of CBM in the research area,the tectonic evolution was revealed to control the overall gas content distribution in the area.The tectonic shape,depth and hydrogeological conditions mainly determine the distribution of gas content in the coal seam.The ESCI parameters were used to quantitatively analyze the permeability and gas barrier properties of the direct top and bottom of the coal seam.The gas control mode of“gentle monoclinic-hydraulic plugging”and“coupling between tectonic conditions and hydrogeology”was proposed.（2）The porosity and permeability characteristics under the formation conditions were simulated and sonic logging and low-field NMR analysis techniques were used to finely characterize the fracture characteristics of coal reservoir pores.The porosity of coal was measured by low field nuclear magnetic resonance（NMR）,and the pore size distribution of coal was analyzed.The permeability of coal was calculated by Coates reservoir permeability calculation model.On this basis,according to T₂ relaxation spectrum of coal,the types of porosity and permeability in the area can be divided into three types.They are single peak and microporosity dominant type,two-peak and mesopores relatively undeveloped type and three-peak pore type.（3）The CBM well drainage curve in the research area was systematically analyzed and divided into five types of rising,decaying,multi-peak,wave-like,and stationary types according to the characteristics of gas wells’drainage curve.According to the complicated dynamic influence factors of CBM production,so we cannot formulate reasonable measures to increase production.The dynamic regularity of coal bed gas well was analyzed and the combination of coal seams with the best combination of effects is preferred.Based on the characteristics of coalbed methane production capacity in the domain,the relationship between the characteristics of gas production in CBM Wells and geological factors,engineering factors and drainage factors was analyzed,and the key geological factors of control capacity in the region were revealed.