Geometry Parameter Designing Of Hydraulic Fracturing In Coalbed Methane Wells

With the development of world economy, the contradiction between supply and demand of energy increases day by day. As the substitution of conventional petroleum resources, the exploitation and utilization of coalbed methane (CBM) draws more and more attention. In despite of the fact that the resource of CBM in our country is very abundant, ranking the second in the world, low permeability and pressure coefficient of CBM reservoir results in low production. Considerable economic benefit of CBM exploiting needs implementing stimulation measures, and hydraulic fracturing is a feasible way. Therefore, adjusting the geometric parameter of artificial fracture to be optimum and creating a high diverting capacity crack which connects the CBM reservoir with the wellbore is significant.On the basis of abundant investigation and research of CBM fracturing data, this paper analyzes and summaries the geologic feature and coal seam fracturing behavior, and then puts forward the coal seam geo-stress forecast model. Besides, considering the structure feature and the complexity of coal seams, this thesis does the basic theory research of crack propagation and establishes CBM well fracturing geometric model and comes up with the corresponding solutions, involving the knowledge of fluid mechanics, linear-elastic fracture mechanics, rock mechanics and computing mathematics. At last, a software of hydraulic fracturing on CBM well is made up. By the use of the software, this paper makes the field design for Well Pu1-2 in QinShui Basin. Meanwhile, in order to describe the effects on fracture geometry distribution, factor analysis is carried out. Field design shows that for coal seam fracturing which has shallow location and high filtration, large pumping rate is needed. In addition, factor analysis demonstrates that in some degree, filter loss will reduce the geometry size of the crack in all three direction. Elastic modulus and Poisson ratio has the same impact on the crack geometry, but the degree of that is different. The former is larger. Enlarging the differential stress between barrier layer and coal seam is in favor of obtaining long wide crack. Large pumping rate can make the crack longer and wider, but height control is necessary. What's more, for coal seam fracturing, artificially increasing differential stress between barrier layer and coal seam and adopting large rate is in favor of high flow conductivity artificial fracture.