Research On Wave Velocity Characteristics Of High Frequency Water Hammer Pressure Wave When Fracturing Pump Is Stopped

The location of hydraulic fractures in fracturing construction is a major requirement for hydraulic fracturing diagnosis.The fracturing diagnosis technology based on water hammer pressure wave is a new fracture diagnosis technology with low cost,simple operation and strong real-time performance.The water hammer pressure wave velocity is the key parameter of this technology.The slight change of the pressure wave velocity will cause a large error in the depth calculation.There are many factors affecting the pressure wave velocity.Therefore,it is of great significance to study the pressure wave velocity variation law in the wellbore in the pump-off section.In this paper,indoor pipeline experiments,ultrasonic grating experiments and numerical analysis methods are used to study the main controlling factors and variation laws of pressure wave velocity in the wellbore in the pump-stopping section.The content mainly includes:(1)The numerical model of pressure wave propagation is established,and the finite difference method is used to track the pressure wave surface to calculate the wave velocity.The numerical simulation results show that the pressure wave velocity increases with the increase of the elastic modulus of the liquid,and decreases with the increase of the liquid density,the liquid viscosity only has a great influence on the pressure wave value.The order of magnitude relationship between the velocity change and the pressure wave velocity is considered in the model,which is slightly smaller than the traditional analytical model.The error is about 17.45m/s,accounting for 1.18% of the analytical model results.(2)Set up indoor and outdoor experimental devices,and form a set of pressure wave velocity experimental analysis methods.Considering the pressure wave velocity experimental results and data stability,the optimal solution for this experiment is the combination of wavelet decomposition and cross-correlation in the dual-sensor method.Function method,for the sampling frequency of 10 k Hz in the experiment,the optimal wavelet basis function is db4 wavelet,and the optimal decomposition layer number is 10 layers.(3)Carrying out ultrasonic grating experiments show that: the change of fracturing displacement fluid type,concentration and salinity will affect the elastic modulus and density of the fluid,and then affect the pressure wave velocity.In the experiment under the same conditions,the pressure wave velocity in the guar gum displacement solution is the largest,followed by slick water,and the smallest in clear water.The pressure wave velocity increases linearly with the increase of liquid salinity.Based on the analysis of previous analytical models and indoor pipeline experiments,it is believed that the pipeline parameters and their stress conditions have a constraining effect on the change of the pressure wave velocity.large and reduced.In addition,the cross-sectional shape of the pipeline and the physical properties of the overlying rock also affect the pressure wave velocity.(4)Design and develop a set of pressure wave velocity calculation software.Based on the input liquid parameters,pipe parameters and construction parameters,the pressure wave velocity in the wellbore in the pump-off section can be calculated in real time,and the variation trend of the pressure wave velocity with different variables can be plotted.Calculate the depth of fluid inflow to the fracture.The field case analysis shows that the liquid system,concentration and system temperature have a greater impact on the pressure wave velocity during construction.In case 2,more accurate fracture fluid inlet depth and wellbore temperature were obtained through the downhole eagle eye equipment.The theoretical value of the pressure wave velocity was close to the actual value,and the error was small.