Multi-branch horizontal well hole docking pressure control extraction technology for close distance coal seam group

CHEN Liang; CHENG Zhiheng; LUO Xin; YU Hongyang; ZHANG Zherui; WANG Peng; WANG Xiangdong

doi:10.12438/cst.2025-0201

Abstract：In order to solve the problems of long extraction time of surface wells in the preparation area of close distance coal seam group and difficult connection of underground boreholes,which lead to the overall imbalance of mine extraction-excavation-mining and limited production capacity.Taking Shaqu well field in Lyuliang city,Shanxi province as an example,through theoretical analysis and data statist-ics,the geological structure of coalbed methane accumulation in the well field,the influence of hydrodynamic conditions,coalbed meth-ane reservoir characteristics and gas-bearing distribution are obtained.Based on the numerical simulation analysis of the extraction effect of multi-branch horizontal wells under different conditions,the reasonable parameters of branch shape,length,spacing,number and angle are determined.A three-dimensional mathematical model for the docking of multi-branch horizontal wells and downhole boreholes was es-tablished,and the analytical solutions of the relative distance and angle between the two were given.According to the drilling inclinomet-er,comprehensive mud logging to ensure wellbore trajectory control and precise drilling,combined with the downhole deep hole cement-ing process and device,the whole process of efficient docking of boreholes was established,and then the pressure-controlled extraction process of positive pressure first and negative pressure second was proposed.The complete set of device for high-pressure buffer tank and multi-stage gas-slag separation tank was developed,and its key parameters and working principle were clarified.At the same time,the comprehensive evaluation function of the application and transformation effect of the technology is constructed,and the three-dimensional dynamic evaluation index and critical value of safety,benefit and transformation from the preparation area to the production area are estab-lished.The results show that:①It is determined that the mixed pinnate and mixed branch wells are suitable for the preparation area and the production area respectively,the branch length is 300～400 m,the number of branches is 4～8,and the angle between the branch and the main branch is 30°.The positive pressure in the early stage of docking extraction is 0.5 MPa,and the negative pressure in the later stage is 20 kPa;②The daily output of single well in the test area of the fifth mining area reached 13 000 m3/d,which was 3.3 times that of conven-tional wells.The safety indexes in the area are reduced to below the critical value,and the No.3+4 and No.5 coal seams are synchronously eliminated.The drilling volume per ton of coal was reduced by 55%compared with the original,the πz in the preparation area and the con-version rate πs in the production area were 93%and 90%,respectively.The overall conversion rate was 83.7%,the production capacity of coalbed methane is increased by 4.65 million m3/a,and 0.5 million tons of high-quality coal are liberated simultaneously.