| The characteristics of unconventional oil and gas resources,such as low porosity,low permeability and strong reservoir heterogeneity,make reservoir development difficult.Horizontal wells combined with hydraulic fracturing technology is the main means to achieve large-scale reservoir development and obtain productivity.Perforation is an important technology to communicate with reservoir and realize industrial oil flow in the process of hydraulic fracturing.The study of the influence of perforation parameters on breakdown pressure law and fracture propagation in the process of hydraulic fracturing in horizontal wells is of guiding significance for on-site construction to reduce breakdown pressure.In this thesis,with the help of three-dimensional discrete numerical simulation software,with breakdown pressure as the main content,the following aspects are studied and analyzed:(1)The stress distribution around the horizontal wellbore considering perforation is deduced by wellbore coordinate transformation,the analytical solution of single hole breakdown pressure is obtained,and the prediction model of hydraulic fracturing breakdown pressure of horizontal well is established.The numerical solution of the model is compared with the theoretical analytical solution by using the field parameters,and the error between the analytical solution and the numerical solution is less than 6%,indicating that the numerical simulation result is feasible.(2)Based on the three-dimensional discrete lattice method,the spiral perforation model of horizontal well is established,and the 0.5m perforation section of a single cluster is selected.By changing the parameters such as perforation density,initial azimuth angle and phase angle,the breakdown pressure law of spiral perforation is analyzed.The spiral perforation model of horizontal well is established,and the main factors affecting the breakdown pressure of spiral perforation are simulated.The calculation results show that there is a non-linear relationship between breakdown pressure and parameters,and the optimized parameters show that the breakdown pressure is lower when the perforation density of horizontal well is 12/m,the initial azimuth angle of perforation is 0°～30° and90°,and the phase angle is 90°～120°.(3)By using three-dimensional discrete numerical model,the differences in breakdown pressure and fracture propagation between oriented perforation and Tristim perforation model are analyzed and compared.The results show that the breakdown pressure of oriented perforation is 4.28% lower than that of spiral perforation,and the optimal azimuth angle of perforation is 0°～30° and 150°～180°.The breakdown pressure of Tristim perforation is 3.48% lower than that of spiral perforation,and 0°～30° azimuth is preferred.(4)The field segment cluster data are selected to establish a single-stage multicluster perforation model for large-size horizontal wells,and the effect of cluster spacing on breakdown pressure is studied.The numerical simulation results show that the smaller the cluster spacing in the single-stage three-cluster perforation model,the greater the influence of stress shadow on the middle perforation cluster.The fracture does not expand at all,and at the same time,the cracks on both sides bend greatly during the initiation,and the corresponding breakdown pressure is the highest.The stress shadow effect of two clusters of perforation in the middle of the single-stage four-cluster calculation model is more serious,considering that the main reason is the pressure drop caused by friction near the wellbore and uneven flow distribution,so the fracture expand is non-uniform. |
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