Fracture Extension Model Of Coalbed Methane Horizontal Well Staged Fracturing

Coalbed methane(CBM)horizontal well staged fracturing can increase the coalbed methane seepage channel,make a greater use of underground coal seam gas resources,substantially increase in the yield of a single well and better improve economic and industrial value of coalbed methane exploitation.But it is not very clear about fracture initiation mechanism and extension mechanism in the staged fracturing of coalbed methane horizontal wells,and there is no corresponding calculation model of crack initiation pressure,crack initiation angle and extension dimension at present.The thesis established a CBM horizontal wells piecewise fracturing around the wellbore stress distribution model with the comprehensive study of the induced stress caused by components of the initial stress field,the wellbore pressure,the fracturing fluid filtration effect and the cracks.the friction caused by perforation in the wall is also been considered.Based on this model have been derived a calculation model concerning fracturing pressure and initiation angle and analyzed the influence of perforation parameters,in-situ stress difference and coal rock mechanical properties on the initiation pressure of coal seam.In the aspect of fracture extension model,the concept of interfacial elastic plastic difference coefficient is introduced,and the three-dimensional model is established for the fracture extension of the horizontal well in the coal seam and programming using MATLAB.Through the example data validation,it is proved that the model of fracture extension in this thesis is very similar to the simulation results of Fracpro-PT software.In addition,the influence of physical property parameters,formation conditions and fracturing conditions on the extension of the fractures in the coal seam is analyzed which of a certain significance to on-site coal seam fracturing.