Optimisation and application of well types for ground development of coalbed methane from no. 3 coal seam in shizhuang south block in Qinshui basin, Shanxi province, China

Determining the optimal well types for ground development of coalbed methane (CBM) is a significant premise from which to reduce construction risk during a project and improve CBM production efficiency. Based on Langmuir isotherm adsorption theory and Darcy's law, the research established mathematical models for productivity of vertical wells and stage-fractured horizontal wells, respectively. In combination with the economic evaluation model, the research proposed an optimisation method for CBM wells through productivity prediction, evaluation of comprehensive economic benefit, and well-type determination. Then, the method was verified based on practical reservoir conditions and CBM production of the developed wells in middle and south of Qinshui Basin (Shanxi Province, China). Meanwhile, charts of CBM production under influences of gas content and post-fracturing permeability using vertical wells and stage-fractured horizontal wells, respectively. The results indicate that, in the Shizhuang south block, when the gas content is less than 10 m(3)/t, CBM wells are not recommended; If the gas content is between 10 and 12 m(3)/t, stage-fractured horizontal wells can be constructed in areas where post-fracturing permeability can exceed 1.27 x 10(-3)mu m(2), faults and collapse columns were not developed, and hydrogeological conditions were not complicated; If the gas content is between 12 and 15 m(3)/t, stage-fractured horizontal wells can be constructed except in areas of mylonite coal; For reservoirs with gas contents between 15 and 18 m(3)/t, stage-fractured horizontal wells are preferred, and vertical wells can be considered in areas where post-fracturing permeability can exceed 0.91. 10 3 mu m(2), faults and collapse columns were not developed; In the case that the gas content exceeds 18 m(3)/t, both types of wells can be constructed, except in areas of mylonite coal. The results allow us to select a suitable method for selecting CBM well types under different reservoir conditions.