Technology and application of staged fracturing in coalbed methane horizontal well of soft and hard coal composite coal seam

Aiming at the problems of low efficiency of coalbed methane extraction in soft and hard coal composite seam and uneven extraction in coal seam longitudinal section,etc,In order to achieve rapid and overall efficient extraction of CBM over a large area. Taking the No. 3 coal seam in Zhaozhuang field of Qinshui basin as an example,this paper ana- lyzes the layered characteristics of soft-hard coal,optimize the local hard coal segment in the composite coal seam. and puts forward the new idea of exploiting CBM through noncementing staged fracturing horizontal wells in layered soft- hard coal seam. On the basis of fracture propagation pattern of fracturing on horizontal wells in layered soft-hard coal seam,the technical measures for the development of CBM by noncementing staged fracturing horizontal wells are investigated. The results show that there are obvious layers of soft and hard coal in No. 3 coal seam. and obvious characteris- tics of natural gamma and resistivity logging response in soft-hard coal. Horizontal well in hard coal fracturing can form a complex and irregular vertical fracture,which is easy to expand and extend along the roof strata with strong brittle- ness. Hydraulic fracturing can break both hard and soft coal seam,and can improve the fracturing effect of soft and hard coal seam. The location of horizontal wells in hard coal and fracturing construction discharge have an influence on the effect of fracture expansion,the influence degree of fracturing discharge is large and the horizontal well position is small. In view of this characteristic,four key technologies for the successful development of CBM by horizontal wells of staged fracturing are formed:① Optimization technology of perforation and fracturing section in horizontal well;② Pipeline transmission large displacement hydraulic jet anti-channeling technology;③ Technology of slug type water carrying sand fracturing with “large displacement,large scale and medium sand ratio”;④ Fine drainage and mining technology for simultaneous production of gas and water well separately. The practice proves that this technology can greatly increase the output of horizontal well of coalbed methane,break through the technical bottleneck of low yield of soft and hard coal composite coal seam,and provide a technical way for coalbed methane extraction and gas disaster control of soft and hard coal composite coal seam.