Fracturing Technology of Coalbed Methane in Qinshui Basin

Abstract Coalbed methane (CBM) reservoir with Lower Young's Modulus, higher Poisson's ratio, and lower permeability is different from conventional sandstone reservoir in composition, structure, tectonic and mechanical property, therefore, the fracturing technique and mechanism are much more different. Qinshui Basin located in the southeast of Shanxi Province is of simple synclinorium structure, less of faults, and it has up to 10 layers of coal seams, total thickness 1.2–23.6m and the maximum 6.5m. By far, No.3 and No.15 coal seam of Qinshui Basin have been developed for CBM production, depth from 600m to 900m, and the rank of the coal are mainly meager-lean coal and anthracite. No.3 coal seam of Shanxi Formation is 0.53–7.84m thick, gas content 11.94m3 / t on average, mainly semi-bright coal and semi-dull coal, reservoir pressure gradient 0.7149MPa/100m on average, well-testing permeability 1.589mD on average, Langmuir volume 39.03m3/t on average, Langmuir pressure 2.902 MPa. No.15 coal seam of Taiyuan Formation is 0.6– 9.9m thick, gas content 12.45m3/t on average, mainly bright coal and semi-bright coal, reservoir pressure gradient 0.7727MPa/100m on average, well-testing permeability 1.14mD on average, Langmuir volume 40.91m3/t, Langmuir pressure 2.5417 MPa. Through optimizing the fracturing designs, evaluating fracturing fluid systems and implementing control measures, a set of ‘network fracturing’ treatments with casing injection, high displacement and activated water fracturing fluid as key techniques were developed and applied successfully for coalbed methane in Qinshui Basin with the rate of success more than 95%. The study also showed that the multi-fracture treatment by plugging perforation with plastic ball can be used in separate layer treatment of coalbed methane reservoir. Furthermore, variable injection rate and slug injection of proppant can also be used to achieve the purpose of controlling extension of fractures. In five years,1264 layers (at 1096 wells) were treated by using this fracturing technology in QinShui Basin, and the gas production rate is over 2000 m3/d in 60% fracturing wells.