Well Pattern Optimization Of Coalbed Methane With Complex Coal Bed Structure

The coalbed structure in the south of Sichuan and the north of Guizhou is complex,with characteristics such as bifurcation thinning and slope.The productivity difference of CBM development well pattern in these areas is obvious,which seriously affects the development effect of CBM reservoirs with complex structure.In this paper,the typical complex coalbed of Muai area in the south of Sichuan is taken as the research area.In addition,theoretical analysis,logging analysis,statistical analysis and numerical simulation are used to study the structural characteristics of complex coalbed in Muai,Sichuan area.Through the analysis of structural characteristics of the complex coalbed and the geophysical methods,the identification and characterization parameters of the complex coalbed structure are proposed,such as the complexity coefficient,the coal inclusion ratio,the coalbed inclination angle and the accumulated coalbed thickness.The characteristics of complex coalbed parameters of different productive wells were analyzed by the statistical method.In detail,the high productivity wells always have low coalbed complexity coefficient,small coal intercalation ratio,low dip angle,concentrated accumulated coalbed thickness and high lower limit value.The influence of various parameters on the development was studied.The structural parameters of the complex coalbed,which can affect the development of coalbed methane,are ranked according importance as follows: accumulated coalbed thickness,coalbed inclination,complexity coefficient and coal inclusion ratio.The optimization model of well spacing was established considering the characteristics of the reservoir controlled by the elliptical expansion of pressure around fracturing vertical well,the principle of equal resource control,economic limit and drilling demand.Based on the analysis of the pressure expansion characteristics of different combination relations between the direction of artificial fracture and the inclination of coalbed.An optimization model of well spacing in inclined coalbed is established based on the principle of equilibrium pressure drop.