Geological characteristics and development optimization of coalbed methane inthe Taiyuan Formation of Gujiao Mining Area

Coalbed methane (CBM) resources in the deep Taiyuan Formation of the Qinshui Basin is significant,while the development is still not fully conducted. Through systematic analysis of the drilling,fracturing,drainage,and other test data of Gujiao Mining Area in southwest Qinshui Basin,the geological characteristics like coal thickness,gas content and physical property of coal in Taiyuan Formation is revealed,as well as the production characteristics like gas emerging pressure and drainage rules. Combining numerical simulations,the favorable development areas are divided,and the well pattern and well pattern design selection are proposed. The main coal seams in the study area have stable distribution,medium thickness of 5 m,moderate burial depth between 500-900 m,low ash and sulfur,strong gas generating capacity and high gas content of 11 m3/t. The coal seam has medium physical property,high gas saturation,high ratio of near reservoir and early time of gas occurrence,which has good development potential. The factors influencing the development of coalbed methane include the concentration of in-situ stress caused by tectonic movement,the difficulty of engineering reconstruction,the low gas pressure of main coal seams,the difficulty of gas desorption,the interstitial drainage during the development process,and the blockage of fractures or pore throats. Based on the resource abundance and gas pressure,the effect of coalbed methane production is simulated. When the reserve abundance reaches 0.4×108 m3/km2 and the gas pressure is greater than 1.8 MPa,the development effect is better and the predicted 20 a cumulative gas production reaches 957×104 m3. The optimum horizontal well criteria are horizontal length of 700 m,8 sections fracturing and 300 m well spacing. When the distance between the directional well and the horizontal well is 350 m,the development efficiency is the best. In the diamond pattern of directional wells,the short axis distance is 200 m,the long axis distance is 300 m,and the development effect is the best. The above-mentioned comprehensive analysis of the geological conditions for CBM development,combined with the integrated geology-engineering design,defines favorable areas and process options for subsequent development,providing geological support for efficient CBM development in the study area and similar areas.