Structural Stress Around Perforated Well And It's Fracture Geometrical Characteristic

In the process of SRV(stimulated reservoir volume)fracturing of unconventional oil and gas resources,the distribution of stress in the near wellbore region is very complex due to the influence of reservoir lithology,wellbore structure,in-situ stress,pore fluid and the distribution of natural fractures.On the other hand,the fracture patterns are various in the near wellbore region owing to the nonlinear mechanical characteristics of reservoir.Based on the continuum damage and fracture mechanics,and considering the complex geometry and nonlinear material characteristic of near wellbore region,a nonlinear rock deformation and damage mechanics model is construct in this paper.Numerical simulation is used to study the distribution of near wellbore stress and fracture geometrical characteristic.Combined with the large triaxial rock mechanics test system,the effect of perforation on fracture geometrical in the near wellbore region is analyzed.The main research work including:(1)Based on elastic-plastic damage constitutive model of rock,the characteristics of deformation and fracture damage of near wellbore is studied.Damage evolution is controlled by cumulative plastic strain.The wellbore structure stress and formation damage process are analyzed.(2)The ABAQUS software is used to establish 3D finite element model about wellbore structure.Dynamic evolution of initial stress and rupture morphology in near wellbore region are studied.Different perforating methods are compared with in-plane perforation.The influence of the parameters of the perforation(the angle between the jet and the hole)on the stress distribution and the initial fracture shape of the near wellbore are analyzed.(3)Based on the element coupling of pore pressure and the birth-death element technology,the process of near wellbore fracture and hydraulic fracture propagation is studied.(4)A 2D hydraulic fracture propagation model of near wellbore is established.With a user-defined subroutine,the fracturing fluid on the fracture surface and the sensitivity of the permeability about rock stress are considered.At the same time,the effects of pumping rate,viscosity of fracturing fluid and reservoir properties on near wellbore hydraulic fracture propagation morphology are also researched.In fractured reservoir,the effects of approximation angle and strength of natural fracture on hydraulic fracture opening displacement and propagation distance are studied.(5)Based on the large triaxial rock mechanics test system,the hydraulic fracturing physical simulation test of vertical well were carried out.Through the recording data of fracture pressure and the fracture morphology scanning pictures of fracture section.The effects of in-plane perforation parameters on initial breakdown pressure and hydraulic fracture morphology are studied.Finally,the physical testing data are compared with the numerical simulation results.