Numerical Simulation of Coalbed Methane Seepage in Pinnate Horizontal Well Based on Multi-Flow Coupling Model

Abstract: The motive of the study is to establish a seepage flow model of pinnate horizontal well in infinite reservoir according to the characteristics of 3D distribution of CBM pinnate horizontal well. Taking flow pressure drop along the main and branch boreholes into consideration, the fluid flow formulas of CBM pinnate horizontal well are proposed. The corresponding calculation program has been achieved based on C++ computer language to analyze the effects of branch symmetry, angle between main and branch boreholes, branch number on isobar distribution, inflow profiles of branch and main boreholes of CBM pinnate horizontal well. The results show that: the isobars present symmetry property by the main borehole when branches are symmetrical. At the same time, production per unit length of main borehole at branch node declines rapidly while the radial inflow curves of branch boreholes are almost the same. With the increasing of angle between branch and main boreholes, isobars transfer into trapezoid from slantwise triangle, meanwhile, the inflow rate of branch borehole increases gradually. Isobars transfer into irregular polygon with the increase of branch number. Moreover, the inflow rate of main and branch boreholes all decreases with the increasing of branch number.