Influences of branch parameters on productivity of CBM pinnate horizontal well

Considering the variable mass pipe flow of the main and branch boreholes,the CBM pinnate horizontal well productivity prediction model was proposed based on 3D gas-water two-phase flow characteristics in the coal seam.The corresponding calculation program is written based on C++ programming language.At the same time,an actual CBM well is simulated as an example.The simulated results are verified by the monitoring data from the actual site.This paper studies the effects of branch symmetry,the locations of branch points,the angle between main and branch boreholes,branch length,and branch number on gas production per unit length of the CBM well.The comprehensive results demonstrate the high accuracy of the computation model,and its ability to meet the actual needs of the project.The characteristics of gas production per unit length along the main borehole is high on both ends and low in the middle,with local decline at the branch point locations,while the characteristic of gas production per unit length along the branch borehole is high at heel,low at toe and increases gradually in the middle.Gas production per unit length at branch locations along main borehole declines faster when branches are symmetrical than asymmetrical.As branch node moves from heel to toe along the main borehole,peak gas production per unit length also transforms from toe to heel.The angles of the main and branch boreholes have no effect on gas production.At the same time,gas production per unit length reduces as the branch length along main borehole increases.Gas production per unit length increases with the distance from branch node to heel end.Gas production per unit length increases with the increase of branch length and the angle between main and branch boreholes.However,it declines as the number of branches increase.