Numerical Calculation And Software Development Of Hydraulic Fracturing In Coalbed Methane Wells

Coal resources in our country are abundant. In addition to release the pressure ofconventional sources, industrial exploitation of coal bed methane which is as aunconventional source can reduce the risk of coal mine exploitation and reduce the emissionsof methane which can cause atmospheric contamination. However, the permeability of coalreservoir and the production of single coal bed methane well is very low in our country. Toimprove the production of single coal bed methane well, the artificial fracture will be createdto connect the natural crack which can connect the coal bed methane reservoir and thewellbore to form a passage of high conductivity capacity by using hydraulic fracturingtechnology.This thesis surveyed and analyzed the geologic characteristics and fracturingcharacteristics，summarizing the initiation and propagation rule of the fracture crack of coalbed. The knowledge about related disciplines of synthesized fluid mechanics, rock mechanicsand fracture mechanics is combined with the model of fracture extension of conventionalfracturing extension, thus proposing the model applied for the predict of fracture extension.Two solution methods are put forward. Since the fracture toughness difference between coalbed and interlayer has insignificant influence on fracture geometry, we assume that the coalbed toughness is equal to interlayer toughness, and simplify the model solution method.Studies show that this method can meet the engineering requirements. Secondly, it simplifiedfracture volume change rate in equation of continuity and compared the operated result withbusiness software result based on the characteristics of the high filtration and low efficiencyof fracturing. The difference between these two methods is small when the filtrationcoefficient has a bigger value; when the filtration coefficient of the coal seam is bigger than0.0006m/min^0.5, the error of the algorithm can be neglected. In order to better predicttransportation of proppant in the coal seam cracks, set up transportation models that proppant in the simulation of three dimensional crack, and carry out numerical solution. By way ofincreasing on-way resistance to avoid considering the intricate pressure drop in cracks in coalseams, for example migration of fine coal, crack stretch and so on, the method can forecastfracturing construction pressure of some block in Qinshui Basin well.On the basis of the research above, software of CBM fracturing optimization design,using the algorithm based on the coal seam characteristics, was compiled with Visual Basic6.0. This software could simulate the geometry of hydraulic fracture in coalbed, predictdistribution of proppant in fracture and calculate frictional resistance of hydraulic fracture inCBM wells. In addition, through calculation of example, conclusions of related theory werereached and the effect on crack expansion, proppant migration and frictional resistance wasanalysis in quantities. To some extent, this software will be of important significance to CBMprophase fracturing design and site construction...