The visual simulation of hydraulic crack width in coal rock and the analysis of influencing factors

To observe and study the geometry of hydraulic fractures directly in coal rock,a hydraulic fracturing simulation experiment was done using the large-scale triaxial fracturing test system in a laboratory.And the MATLAB software was used to simulate the geometry of fractures to obtain the images of cracks.The images of cracks indicate that the width of cracks is suitable for the PKN model.When the cracks are open,a new model was built to get a new equation of the width.Then a Spline Interpolation method was employed to get a fitted value.The comparison show that the fitted value is close to the theoretical value that we get from the new equation.Finally,the relationships between the width of cracks and the factors (permeability,the width of natural fissure,adsorption deformation,temperature) were analyzed and deducted,which indicates the width of hydraulic cracks will decrease with the increasing value of permeability,the width of natural fissure and adsorption deformation respectively.