Development practice of deep soft coal CBM in Qinshui Basin

The development of coalbed methane in China is mainly concentrated in areas with coal seam depth less than 1 200 m,and no substantial breakthrough has been made in deep coalbed methane with burial depth greater than 1 500 m. In view of the problems of poor stability of deep soft coal shaft and difficult fracturing reconstruction, a series of technical breakthroughs have been carried out on the development of deep soft coal bed methane in Qinshui Basin. The results show that in the drilling process,the drilling fluid system of “KCl polymer + borehole strengthening agent” can effectively control the relative borehole diameter expansion rate of coal seam. Use 16 m3 / min to 18 m3 / min ultra-large displacement,high liquid volume and high sand volume smooth casing fracturing technology,combined with resistance reducing agent to reduce construction friction. The proportion of fine sand,medium sand and coarse sand is 15%,70% and 15%. The amount of sand added to the total sand carrying liquid volume ratio has been gradually increased since 3%, increase by 1% each time, which can realize the full transformation of deep soft coal. The maximum dynamic half length of the fracture reaches 322. 51 m, greatly increasing the control area of a single well,and the effect of gas drainage and production is good.