Perforating Pressure Pulsation And Dynamic Response Mechanism Of Tubing And Casing In High Pressure Deep Well

The reservoir pressure of high-pressure deep well over 5000 m depth is more than 70 MPa.Because of long contact time between the drilling fluid and the reservoir rocks,there often forms a contaminated zone with blocked pores and decreased permeability.Thus,it is required to use shaped high energy perforating cones to penetrate the contaminated zone.During perforation the detonating gas with high energy and high pressure would induce complex impact loads,which acting on the tubing and the casing may result in plastic bending or even smash of the tubing as well as damage of the casing.The detonating gas will crush the cone cover and form a metal jet with pressure up to Giga Pascal and speed higher than ten thousand of meter per second,which will penetrate the perforating gun and lead the gun expansion or even being stuck.The cost of this kind of unanticipated abandoned well is up to one hundred million Yuan.The existing underwater explosion theories for shallow water,low initial pressure and free boundary are insufficient to solve these problems under deep well with high initial pressure and narrow inner boundary.Therefore,according to the characteristics of perforation in high-pressure deep wells,the pressure pulsation of the perforating fluid and the dynamic response mechanism of tubing string are studied,which would guide the perforation design and operation to reduce some accidents,Which is of great significance to the perforation safety and the reduction of cost.(1)Study on detonating parameters and pressure pulsation law of perforating fluid in high pressure deep wellBy applying Mihelison equation and the average specific heat capacity method of detonating components,the maximum degree of realization coefficient of detonating is introduced to modify the detonating capacity,detonating heat and detonating temperature.By using maximum energy releasing principle and Kamelet method to analyze detonating pressure and velocity,a suitable detonating parameter analysis method for jet perforating explosives was established,and the analysis accuracy was improved.Considering the influence of high pressure and narrow casing boundary of perforating fluid on shock wave propagation,considering the interference of perforating jet array and considering the continuity of shock wave at phase change interface,the initial pressure analysis method of shock wave was formed based on Tait equation.Based on reflection principle,a method for analyzing the interface reflection parameters of casing and perforating fluid was established.By applying the superposition principle of direct wave and reflected wave,considering the interaction of initial wave,reflected wave and superposition wave,the pressure pulsation analysis method of shaped charge perforating fluid was established systematically,and the perforating pressure pulsation law was expounded.It is shown by calculation example that the pressure of reflected wave increases with the decrease of explosion distance,and the pressure of reflected wave is larger than that of incident wave.Taking the 16-hole /m perforation scheme as an example,the influence of four other perforating cones near the first perforating cone on the detonating shock wave of the first jet was bigger and should not be neglected,and the pressure attenuation time considering the jets interference was extended by 30 μs.(2)Analysis of the influence of superposition of perforating cones on the strength of perforating gun and perforated casingDuring perforating,perforating gun and casing will be penetrated by metal jets with pressure up to Giga Pascal and speed up to ten thousands of meters.Using Ls-dyna module of ANSYS software,the 3D model of perforating cone-perforating gun-casing was established.The improved ALE operator separation was applied.Each iteration was divided into two steps.First,the Lagrangian algorithm of the mesh moving with the matter was implemented,and then the Euler mapping algorithm of the mass,internal energy and momentum across the cell boundary was executed.Considering the fluid-structure interaction,the effects of detonating on energy,density,jet velocity,perforating gun and casing strength were analyzed.Numerical analyses show that the superposition among the perforating cones can greatly increase the perforating energy.The strong the interaction between perforating cones,the thorough the detonating is,which is of great benefit to increase the depth of perforations.When the interaction among three perforating cones were superimposed on each other,casing stress may exceed the yield strength of casing material,and the strength yielded ring was larger than that of single one with a width of 2.5 mm.After perforating,there is outer burr on perforating gun and inner burr on casing.If the gap between the outer wall of perforating gun and the inner wall of casing is less than the sum of the outer burr and the inner burr,the gun will be stuck.The minimum stress between holes of perforating gun was already exceeded the yield strength of gun material.Under the action of high detonating pressure,outward bulge will be generated and the so-called bulge gun will occur.(3)Analysis of residual strength of repetitively perforated casingApplication of deep penetration,large-aperture,high-density perforation may "regenerate" some abandoned wells.Repeated perforations reduce the strength of the casing,and if the strength is decreased too much,a large volume fracture cannot be performed.To this end,a three-dimensional finite element analysis model for perforated casing was established taking a renewable deep well as an example,considering three disadvantageous distributions of repeated perforations,namely axial,circumferential and helical tangency.The boundary element processing method was applied to deal with the problem of difficult convergence of hole tangency.The residual strength of the secondary perforated casing and the tertiary perforated casing were obtained.Numerical analyses show that the axial tangency of first and repeated perforated holes is the most unfavorable repeated perforation with the largest residual strength reduction.The residual strength of the secondary perforated casing is decreased by about 20%,and the residual strength of the tertiary perforated casing is decreased by about 30%.(4)Study on dynamic response mechanism of perforating tubing string under perforating pressure pulsation excitationBy applying the cantilever theory of vibration mechanics,the dynamic model of perforating tubing string exerted by perforating impact load was established,and the differential equations of longitudinal,transverse and torsional vibration of perforating tubing string were derived.The natural frequency,main mode and displacement dynamic response expressions of perforating tubing string vibration were obtained by using the separation variable method.Using AUTODYN module of ANSYS finite element analysis software,the finite element transient model was established.The Euler model was used to describe the solid wall boundary of casing and the elastic material tubing string.The Euler-Multimaterial model was used to describe the large deformation of perforating fluid and the solid liquid phase changing of perforating cones,the automatic perforating cones and the fluid-solid coupling.The pressure pulsation of perforating fluid and the dynamic response mechanism of perforating tubing string were studied.The plastically bended even broken perforating tubing string near packer was clarified.Taking P110 S tubing material which is commonly used in oilfield as an example,the mechanical properties of the tubing material under the impact of high strain rate were tested.The experiment results show that,under the strain rate of 500 s-1,the yield strength of the tubing material is 15.5% higher than that of the static measured value;corresponding to perforating tubing string vibration caused by dynamic load,the strength was decreased by 4.5%.Under the dynamic load of strain rate of 1000 s-1,the yield strength of the tubing material is 41.4% higher than the static value;corresponding to perforating tubing string vibration caused by perforating impact,the strength decreased by 8.6%.(5)Study on the perforating pressure and the vibration of perforating tubing string by measuring in high-pressure deep wellAn innovative downhole tester for perforating pressure and string vibration was developed to solve the technical problems of high frequency sampling and large range acceleration measurement under high temperature and high pressure.The tester was tripped into a depth of about 5000 m underground along with the perforating-testing string,and the pulsating pressure of perforating fluid and the vibration acceleration of perforating tubing string during perforating were continuously measured and recorded.The error of peak pressure of perforating fluid between measured value of theoretical analysis is less than 9.5%,while the error of upward axial acceleration is less than 6.0% and downward axial acceleration8.4%.This shows that it is feasible to simulate perforating and detonating analysis by Euler and Euler-Multimaterial coupling algorithm.