Numerical Simulation On Gas-water Flow During The Development Of Coalbed Methane In The Zhengzhuang Block

The southern part of the Qinshui Basin is one of the most successful areas for the commercial development of coalbed methane in China.Among them,the exploration and development of coalbed methane in the ZhengZhuang block is relatively high,but in the actual development process,the proportion of high-yield wells for coalbed methane wells is generally low,and a large number of them appear.In order to analyze the causes of such problems,this paper will combine numerical simulation methods and actual field data to study the influencing factors and control mechanisms of coalbed methane drainage and production capacity.Quantitative analysis of the factors affecting the gas production of coalbed methane wells in the ZhengZhuang block.Based on the statistics of evaluation wells in the block and development wells in the five well areas,the overall geological conditions of the coal seam depth,thickness,stress,porosity,etc.in the ZhengZhuang block and the output of the CBM wells were analyzed,and the output of the CBM wells was obtained.The influencing factors are mainly controlled by the gas content.According to the water production rate in different well areas,it is concluded that Zheng 1,Zheng 2 and the Eastern Area have higher water production rates.It indicates the possibility of external water supply.Based on the effective stress principle and matrix shrinkage effect,the coal rock deformation control equation is established.Based on the effective stress principle,the mechanism shrinkage effect,and the gas slip effect,the coal seam two-phase dynamic porosity and permeability equations are established.Based on the material balance principle,the coal rock mass is combined.The deformation control equation establishes a Multiphysics field coupled model of coal-bed two-phase seepage,and is verified by actual evaluation well test data.The result shows that the model can be used for the whole process of single-phase and two-phase flow of the coal-bed gas well.The established models simulate the dynamic changes of coal reservoir pressure,porosity,permeability,water saturation under different Young's modulus,different initial permeability,different critical desorption pressure,different drainage systems and well gas production.It is obtained that the initial permeability is a direct influencing factor of gas production.The critical desorption pressure has a greater control on gas production,and the control of coalbed methane production by different Young's modulus is relatively limited.The high-pressure drop rate in the two-phase process has positively helped the early daily gas production of CBM wells,but once the wellbore flow pressure no longer changes,the daily gas production will rapidly decay.Therefore,the high-pressure drop rate is not conducive to the stable production of the CBM well as a measure of early drainage and pressure reduction.A three-stage change in the pressure drop expansion rate was found,which was more pronounced at high Young's modulus,low permeability,and high drainage rate.