Optimization Model Of Quantitative Drainage System For CBM Vertical Wells In Zhengzhuang Block

The thesis studies on fracturing CBM vertical wells in Zhengzhuang Block of Qinshui Basin.On the basis of ascertaining the coalbed methane geological conditions,combined with the hydraulic fracturing and drainage data,the drainage type of the CBM vertical wells in study area could be classified into four types with the principal component analysis method.The production capacity is mainly controlled by the burial depth,groundwater fluid potential,permeability,gas content and fracturing construction factors.Combined with the permeability sensitivity test,the response surface method and the maximum likelihood function method were used to achieve an accurate calculation of the effective stress coefficient(ESCK)of coal permeability.The ESCK increases with the increasing of water saturation.Based on the unsteady-state method of gas-water relative permeability measurement and fractal geometry,an improved fractal model was proposed to fit the gas-water permeability under different confining pressures after performing a compressibility correction of the mercury intrusion volume.On the basis of the detailed description of desorption,the drainage process of CBM wells could be divided into initial drainage phase,rapid gas production phase and sensitive gas production phase.According to the production data,a dynamic analysis method for fracturing CBM vertical wells was built.The pressure drop law and desorption range of the reservoir during the initial drainage stage and gas-water two-phase flow stage were analyzed.The backstepping of effective permeability of reservoir was achieved,which was compared with the dynamic change of permeability obtained by the experimental theory.The key of drainage system setting is to control reservoir desorption capacity and seepage ability match each other.Based on the established dynamic analysis model of the drainage process,a stepwise quantitative formulating method for drainage system of the fracturing CBM vertical wells in the study area was proposed.The quantitative calculation of pressure drop rate at the bottom of the well during the drainage process was achieved,which provided a theoretical support for reasonable excavating CBM well productivity.