Comparative analysis of gas/water fracturing crack extension based on fracture fractality
In order to explore the difference between the initiation and propagation of gas/hydraulic fractures,water and N2 fracturing experiments with sandstone and shale cores were designed and carried out,and the influence of fluid flow laws and fracture fractal effects on breakdown pressure and fracture morphology were analyzed on.The following experimental results were obtained:l)The flow rate is negatively correlated with the ratio of the N2 flow radius to the clear water flow radius(RN/Rw)under the same injection pressure;however,the injection pressure is positively correlated with RN/Rw at the same flow rate.2)Under the same rock particle size,the fractal dimension difference of the gas/liquid hydraulic fractures is negatively correlated with the ratios of the tensile strength of the rocks under the gas/liquid hydraulic fractures(σtg/σtl);however,the smaller the σtg/σtl gradually increases until it is constant with the particle size increase.The following conclusions were drawn according to the analysis results:1)The flow radius of gas is much higher than that of liquid based on the low viscosity and high compressibility of gas,which strengthens the influence on pore pressure;2)The gas intrusion size in fractures is much smaller than that of liquid,and the fractal dimension of gas fracturing fractures is larger,which reduces the tensile strength of the rock.So,the fractal dimension of fractures should be considered in fracturing,especially in gas fracturing,to reduce the calculated value of breakdown pressure.
万方数据
维普
