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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 analyzes 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 characteristics 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 brittleness. 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. [ABSTRACT FROM AUTHOR]

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 bore-holes, 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. [ABSTRACT FROM AUTHOR]