Analysis on potential geological mining model of deep coalbedmethane in Linxing Block

The deep coalbed methane resources in the central part of Linxing which lies in the eastern margin of Ordos Basin are potentially abundant. Based on the geological evaluation of coalbed methaneand the effect of single well test in this area, this paper describes the gas and water output characteristics of the deep coalbed methane well, and then analyzes the geological factors affecting the productivity of single wells. This paper focuses on the geological factors controlling the production of deep coalbed methane wells in terms of crack distribution and stress characteristics. Then, it describes the matching relationship of multi-type gas layer (tight gas layer and coalbed methane) of coal-based gas to discuss the potential recoverable geological models of deep coalbed methane in the area.The research shows that:①The potential of coalbed methane resources in the block is relatively large, with characteristics of thick coal seam, high gas content, good coal quality, good sealing of coal rock roof and bottom, and water retaining environment. But, high stress,poor porosity and permeability are the main geological factors that restrict the exploitation of coalbed methane in the area.② Due to the large coal seam stress in the deep coal seam, it is difficult to effectively fracture the coal seam with the single-pressure coal seam mode dominated by conventional clean water fracturing in vertical wells and the production effect is poor. The development effect of deep coalbed methane can be improved by the mode of “double pressure sand bed poor gas layer and main mining coalbed methane”. The gas production curve of the vertical well is still dominated by the typical form of coalbed methane, and it has the characteristics of “quick gas production in a single well, high water production, easy stress sensitivity and slow increase in gas production”.③ The micro-fracture development zone of the coal-bearing strata is the potential area for the single-well breakthrough in deep coal seams.Based on the existing experience of gas well development in Linxing Block, two potential geological mining models have been explored. Among them, the type Ⅰ geological mining model of “endogenous and external storage type” is the realistic and feasible geological mode for the mining of deep coal seams in the region.The type Ⅱ of “endogenous external storage type” geological mining model and the “endogenous internal storage” type Ⅰ geological mining model are potential replacement modes for the later mining of deep coalbed methane.