The Engineering Characteristics Of Coalbed Methane And Its Production Control In Binchang Area

China has abundant low-rank coalbed methane resources with low degree of exploration and development,low-rank coalbed methane wellproduction controlis still in its groping stage.Based on coal sample test resultscombined with dynamic production analysis,production data and drilling engineering references,this work investigated pore fissure system,accumulation feature,production characteristics and production control method,gas reservoir development model with gas reservoir engineering critical factors inBinchang area,providing the basis for the development of coalbed methane resources in this area.On the basis of integrated use of multiple modern tests and theories,this work studied the entire pore-fracture system in Binchang area.Results show that the coal samplesare characterized by equilibrium pore diameter distribution,dominatedby well-connected pores with the pore shape asink-bottled,cylindrical and parallel plate pores.NMRrevealed an average total porosity of 12.3%,mesopore and macropore ratio averaged 55.7%,which make it favorable for methane adsorption,desorption and diffusion.Further research has been done on the sedimentation,tectonic evolution and structural feature,hydrology geological condition,coal seam roof and floor sealing performance,and the relationship between the gas content distributionand the above four factors.Based on the analysis of actual production data,the productionfeatures of low rank CBM Wells were analyzed.The differences in the dynamic change of permeability,the matrix shrinkage effect on gas production,drilling fluid damage mechanism,desorption time and pressure drop spaceresult indistinct production charateristicsof high-rank and low-rankCBM Wells."Six stages" control method was proposed,based on the weak stress sensitivity of coal reservoirpermeability,strong matrix shrinkage effect on gas production,small amount of coal powder andthe analysis of existing production wells.Gas production and recovery factor of vertical wells,U well and multi-branch horizontal wells were compared through reservoir simulation.The results show that multi-branch horizontal well is the proper way to develop thecoalseam gas,and the optimal multi-branch horizontal well structure is 200-300 m branch spacing,with the angle between the branch and the main legas 60 degrees,dendritic or herringbone multi-branch horizontal well withonly one differnce in branch arrangement can produce the same amount of gas as well aswellbore stability.In addition,the correlation between 12 geological andengineering factors and the peak gas ratewere examined using the grey theory.