The Stress Distribution And Damage Around Definite Plane Perforating Well

Horizontal well perforation technology is widely used in the low permeability oil and gas field exploitation as a new technology. Insight into the fracture control mechanism and relationship between the influence factors and hydraulic fracture extension has important theoretical and engineering value to perfect the relevant technology.Influenced by the reservoir rock properties, the distribution features of the in situ stress, the wellbore structure, the natural fracture and the fluid and so on, the stress distribution around wellbore is complicated. The stress distribution and damage of wellbore with the variation of definite plane perforation parameters is studied in this paper based on the numerical analysis and experimental simulation method. The main work includes:1. Considering the complexity of the nature rock properties, a calculation model of the mathematics of the reservoir pressure about hydraulic crack fracture form and crack angle is established by simplifying and assuming the rock conditions. And the influence of the tectonic stress distribution on the fracture initiation and the propagation morphology are studied.2. Through the numerical simulation method, the influence of horizontal well perforation parameters (perforation phase angle and azimuth angle) on surrounding rock stress distribution is quantitative analyzed. It provides the basis to calculate the horizontal wellbore initiation fracture pressure, crack fracture azimuth, and the optimization of perforating parameters.The studies show that the initiation fracture pressure increases gradually with the increase of the phase angle because of stress superposition weakened between the perforating holes. The control of crack propagation direction is stronger in that the influence of the increased perforating surface area. Under the condition of phase angle fixed, the initiation fracture pressure of surrounding rock shows increasing trend after reducing first when azimuth angle increases gradually. The initiation fracture pressure of surrounding rock is minimal when azimuth angle for 25°.3. Based on the elastoplastic damage model to describe strata rock damage around wellbore, the influence of the perforation phase angle and azimuth angle on the morphology of surrounding rock damage fracture is analyzed.Researches show that the crack of surrounding rock appears first at the middle of the perforation hole under different stress distribution conditions. And the crack locates at the root of the perforation hole. With the process of liquid injection, the crack propagates deflecting to form a fracture face joint with the cracks of the holes on the other sides that is vertical with the axis of the wellbore. With the increase of perforation phase angle, the surface damage distribution area of three perforation holes is decreasing gradually. This is because the stress superposition between perforating holes weakened with the increase of perforation hole phase angle. With the increase of azimuth angle, the wellbore wall rock damage shows a trend of decrease after the increase firstly.4. Through large size true tri-axial rock mechanics test system, a vertical surface perforating hydraulic fracturing physical simulation experiment is carried out. The impact of perforation parameters on initial fracture pressure of reservoir and the fracture morphology are analyzed by comparing the determinate fracture perforating pressure and fracture scanning section with the results of numerical simulation.Researches show that the stress interference between the perforation hole is bigger with small phase angle, and it causes the increase of the complexity and initiation fracture pressure and the deflecting crack propagation. With the increase of perforation phase angle the influence of the horizontal maximum principal stress on both sides of the perforating holes increases gradually. With the process of liquid injection,the tensile damage of the perforating surrounding rock decreased gradually. The crack appears first at the middle perforation hole and extend, forming a smoother fracture with a decreased crack pressure.Compared with the 30° phase angle, the initiation fracture pressure of 60° phase angle is reduced by 4.2 MPa.