Analysis on well type structure and optimization of associated drilling technology of CBM horizontal wells

Horizontal well is the key technology for the efficient development of CBM.In order to optimize the horizontal well types and related drilling technology and increase the production of CBM wells，based on the basic development principles of coalbed methane drainage and pressure reduction gas production of CBM development，the basic optimization principle of CBM horizontal well was put forward，the advantages and disadvantages of all types of CBM horizontal well were studied，and an optimized drilling process methods was proposed for efficient horizontal well types.The results show that the optimization of well types and drilling processes should follow the following principals such as facilitating water drainage and depressurization，increasing the gas-production area，boosting the stability of borehole and cutting down the cost.V-type wells，L-type wells were compared with other well types，sharing or eliminating vertical wells，which greatly reduced costs；.from multi-branch wells to single wells，casing and screen completions were achieved，and horizontal wellbore support was achieved..With the variation from multi-branch to stimulated single branch type，a large gas production area was maintained.L type well will be the promising type in the future，but due to the poor drainage technology of L-type horizontal wells，V-type horizontal wells were the most efficient and suitable horizontal well type at present.It is an effective technology for coal mine gas drainage，which can be promoted on a large scale..The drilling process was changed from three to two，and a large ϕ444.5 mm drill bit was adopted，resulting the diameter of horizontal borehole increase from 139.7 mm to 339.7 mm，which improved the gas production greatly.Through the straightslope cementing technology，the completion of the horizontal coal seam without cementing and sieve tube and casing completion was achieved，which laid the foundation for protecting and improving the reservoir permeability in the horizontal section.This process technology was used in the southern Qinshui Basin and the eastern margin of Ordos Basin，and better results were obtained.