Gas analysis of deep coalbed methane and its geological model for development in Linxing Block

Depth of coal seams in Linxing middle area of the east margin of Ordos is more than 1 000 m,which has reached the research field of deep CBM. Based on the actual production data,this paper discusses the gas bearing ca- pacity of deep coal seam,and refines the development geological model of deep coal seam in the area. The study shows that critical depth of the deep coal seam divided by the turning of gas content is about 2 000 m in the work area. Ad- sorption sensitivity of deep middle coal rank reservoirs is less sensitive to temperature than the pressure,so that critical depth of medium rank coal seams is relatively deeper than that of high rank coal seams. Deep coalbed gas is still main- ly adsorbed gas,and the existing isothermal adsorption testing method is easy to cause the misunderstanding of the pro- portion of free gas in deep coalbed methane. Due to the influence of temperature,the deep coal seam is relatively high in temporary storage ratio. Due to the influence of stress,the reservoir properties are poor. The gas wells generally have the characteristics of “quick gas seepage,difficult drainage pressure reduction and slow gas production increase”. The potential of deep coalbed methane is huge. The experience of gas well shows that rational and optimized development unit is the key to the single-well breakthrough in deep coal seams. The enriched development geological model associ- ated with Type A “source-reservoir” is a development model that is mainly considered in the breakthrough of deep seams.