Research On Mechanism Of Casing Damage Of Perforating Hole In Oil Reservoir

The main purpose of the perforation is to open the reservoir,establish the connection between the reservoir and the wellbore,and allow the fluid in the reservoir to enter the wellbore.At present,the commonly used perforating method in the development of oilfield water injection is spiral perforation,that is,spiral perforation along the axial direction of the casing.For unconventional reservoirs,in order to reduce the hydraulic fracturing initiation pressure and artificially control the near-wellbore fracture morphology,it is proposed that The new perforating process-sizing perforation.At present,the effect of the process on the strength of the casing is less studied.This paper studies the effect of the fixed-surface perforation on the strength of the casing and provides a theoretical basis for the perforation of unconventional reservoirs.In order to study the effect of rock on the strength of perforated casing,this paper combines the rock mechanics,elasto-plastic mechanics,damage mechanics and seepage mechanics based on fluid-structure interaction theory to establish a stress-coupling model for formation-cement ring-perforated casing.,Degradation is compared with the naked cannula and the API standard,which verifies the feasibility of numerical simulation.It is found that the ability of the cannula to withstand internal pressure is increased by 1.48-2.16 times while considering the constraints of the formation.Therefore,in the analysis of perforating casing strength under pressure,the influence of the formation on the strength of the casing after cementing can not be ignored,and the constraint of the formation on the casing must be considered.According to the verification calculation of casing damaged wells in Daqing Oilfield,casing deformation rate was calculated and the accuracy of the model and analysis method was proved.Based on this,the effects of spiral perforation and perforation on the internal pressure and external compressive load of the casing under different conditions of fracturing and oil production were studied.The different casing sizes and perforation parameters were analyzed.The effect of post-hole casing strength.For the same perforation parameters,the spiral perforating and the perforating sleeve strength were compared,and the perforation parameters satisfying the strength of spiral perforation were satisfied.Calculations show that under the same parameters,the smaller the inner diameter of the casing and the thicker the wall thickness of the casing,the higher the residual strength of the casing subjected to the internal pressure and the external extrusion load;In the fracturing condition,when the spiral perforation phase angle is 45° or the included angle between the perforation perforations is 30°,the casing can withstand the strongest internal pressure.Under oil production conditions,the spiral perforation azimuth angle is 45°,and the perforation perforation eye angle is 60°.After the perforation,the casing bears the maximumresidual strength of the external extrusion load.With the same casing size and perforation parameters,the perforation process of perforation makes the strength of the casing after perforation decrease more,but the strength of the casing equivalent to the spiral perforation can be achieved by reducing the perforation diameter or controlling the included angle of the perforation.The results of the above research provide theoretical basis for field application of the perforation technology in unconventional reservoirs,and have good application value for improving the fracturing effect.