Geological Characteristics And Favorable Areas Optimization Of Coalbed Methane In Qiyuan Mining Area,north Qinshui Basin

Qiyuan mining area is located in the north of Qinshui Basin.Based on the data of production wells and parameter wells in the study area,combined with the regional geological structure properties,this paper expounds the heterogeneity characteristics of coal reservoir development in detail.Based on the drilling,fracturing,drainage and other engineering construction parameters of coalbed methane wells,the engineering properties of coalbed methane wells are evaluated.Based on the development characteristics of coal reservoir and engineering attributes of coalbed methane well,the favorable areas suitable for coalbed methane development are divided to guide the later development of coalbed methane.The target coal seams in the study area are No.9 and No.15 coal seams of Taiyuan formation,which are relatively stable.The buried depth of coal seam is shallow,ranging from600 m to 1000 m.The average thickness of No.9 coal seam is 2.9 m,the average thickness of No.15 coal seam is 3.3 m,and the gas content is 13.5 M 3/ The average gas saturation of No.9 coal is 68.97%,and that of No.15 coal is 77.39%.The gas saturation of No.9 coal is high,the gas production potential is large,and the recoverability is good,which is conducive to the commercial development of coalbed methane.Good gas production can be obtained through fracturing or other suitable stimulation measures and processes.Coalbed methane wells in the area adopt the secondary well bore structure,and the drilling adopts the low viscosity and low solid polymer mud system as the circulating medium to meet the operation requirements,but there are some problems such as poor drilling efficiency and low ROP.The fracturing operation in the area is relatively smooth as a whole,with an average sand addition of 48.91m3,an average sand ratio of 12.87% and a discharge rate of 7.66m3/min in No.15 coal seam.However,as the roof and floor of the coal seam are mostly limestone and siltstone,there is a risk of pressure penetration or communication.From the past drainage history,the gas production of single well is generally low,but there are also high-yield wells.A reasonable drainage system is conducive to the stable and balanced production of coalbed methane.According to the characteristics of coal reservoir heterogeneity,combined with the engineering properties of CBM drilling,fracturing and drainage,the favorable areas for CBM development are divided.It is considered that the northwest and southeast of the study area are the most favorable areas for CBM development,followed by the central area,and the northeast and southwest areas are poorer.