Simulation and Structural Parameter Optimization of Coalbed Methane Multi-branch Horizontal Well Production

Abstract The stimulation of coalbed methane (CBM) through multi-branch horizontal wells has been widely used in China. However, its effectiveness in high-order coal reservoirs in the Wenjiaba area of the Zhina Coalfield, Guizhou Province, requires further investigation. This paper develops a numerical model to evaluate CBM recovery and optimize wellbore structural parameters for the 16# coal seam. Firstly, CBM production, content, and gas pressure were selected for an integrated evaluation of extraction applicability. Then, an optimization study concerning structural parameters was conducted, such as branch length, branch angle, and branch spacing. Results show that multi-branch horizontal wells significantly enhance extraction efficiency of CBM. Notably, there is a negative correlation between the CBM content and the distance from the main branch well and this decrease rate exhibits attenuation over distance; A pronounced depressurization zone forms around these multi-branch wells; At greater distances along the wellbore, the CBM flow velocity diminishes leading to a relatively slower pressure relief rate, due to the frictional resistance. Optimizing branch length and angle significantly improves recovery performance.