Study On Prediction Of Deep Coalbed Methane Production Capacity And Dynamic Change Law Of Reservoir Permeability In Linxing Block

China is rich in deep CBM(coalbed methane)resources and has great development potential.However,the deep coal reservoir is located in the complex environment of high temperature,high pressure and high in-situ stress.The productivity of deep CBM Wells is obviously different and the overall gas production effect is poor.Therefore,aiming at the linxing block,a typical deep CBM block in the eastern margin of ordos basin,this paper studied the geological conditions of coal reservoir,the prediction and dynamic analysis of coalbed methane well productivity,and the dynamic change law of reservoir properties.The details are as follows:1.The main coal seams in the study area are 4+5# coal and 8+9 # coal,which are developing steadily in the whole area.The burial depth of 4+5# coal is generally greater than 1600 m,The burial depth of 8+9# coal is generally greater than 1700 m,and can reach 2000 m in some areas.The depth of two sets of coal seams increases gradually from east to west,which belongs to deep coalbed methane Based on the summary and analysis of the temperature and pressure conditions of the deep coal reservoir,the coal quality characteristics,and the CBM adsorption capacity,the preliminary comparison of the two sets of main coal seam accumulation conditions is realized.Generally,the 8+9# coal seam of taiyuan formation has better resource potential than the 4+5# coal seam.2.Using Comet numerical simulation software,the productivity fitting and prediction of typical CBM Wells in linxing block were carried out.A-8 Wells,A-14 Wells gas production effect is good,A-1 well gas production effect is poorer.Preliminary comparison shows that the permeability of A-1 well is too low,resulting in its capacity cannot be fully utilized.This paper analyzed the dynamic characteristics of coalbed methane production,summarized the dynamic characteristics of deep coal reservoir development,and analyzed the production mode division and productivity evaluation.The CBM Wells in the study area are divided into three production modes: A,B and C.The different production modes have obvious differences in gas production peak,stable production time,curve fluctuation and other characteristics.According to the average daily gas output and maximum daily gas output,the CBM well productivity in the study area is divided into three categories and five subcategories.3.Through the establishment of the material balance equation,the study on the dynamic change law of reservoir physical properties during the development process is realized.In the A-8 well and A-14 well,the reservoir pressure drops greatly,and the gas is fully desorbed into the crack to participate in the two-phase seepage,while the pressure drops slightly in A-1 well,and the gas saturation in the crack is difficult to increase.The permeability of coal reservoir is affected by effective stress effect,matrix shrinkage effect and gas slippage effect,showing the trend that reduces first then bounces.Due to the low initial permeability,the reservoir pressure of well A-1 is difficult to decrease,and the permeability is always in the declining stage,further forming a negative feedback to inhibit the production increase.Linxing block is rich in coalbed methane resources,and the above research work further clarifies the coalbed methane resource potential and development trend in the research area.The research results not only provide theoretical basis for the release of deep CBM resource potential in linxing block,but also have reference significance for the exploration and development of other deep CBM block in China.