Dynamic Response Of String Under Perforating Pulse Load

Large amount of energy is released when charges explode during perforating operation,part of which is for perforation to form an oil and gas tunnel between the wellbore and formation.And the other part generates shock wave that is released in the wellbore,which causes strong shock and vibration on string.The heavy impulse load is a main factor for string bending,deformation,fracture and even well accidents.So the dynamic response of downhole string under pulse load has been a critical issue closely related to oil and gas wells normal operation.Aiming at this aspect,the paper has conducted the following work:1.According to the charge explosion properties and the structural features of the string,corresponding theoretical analysis on shock wave,stress wave was made and the propagation rules of detonation wave and stress wave in the string was obtained.2.Considering external load,the structure of the string itself and wellbore,operation parameters and other factors,using the infinitesimal body analysis method to analyze the pipe string static buckling behavior in three dimensional curved wells.Also dynamic bulking theoretical analysis of the string under shocking load was made.3.The ANSYS/LS-DYNA software was used to dynamically simulate perforating process in horizontal well.The fluid-structure coupled large deformation problems during the perforating jet formation,movement and penetration are analyzed by using ALE algorithm.Eventually the variation curve of shock wave with time was extracted.Then a orthogonal test was designed to analyze the five factors of perforating charge loading dose,perforating initial pressure,casing thickness,packer position,formation elastic modulus impacting on the peak value of perforating pulse load.4.The ANSYS/LS-DYNA software was used to simulate the perforated string dynamic response under pulse load in horizontal well.Then the displacement,velocity,deformation and stress changes with the time was extracted when the string was shocked.5.The string was divided into space beam elements to get a finite element model of the nonlinear contact between string and wellbore by introducing bidirectional spring elements in every unit node.Simulation was done to analyze the dynamic response of the string in horizontal wells under pulse load and get the distribution curves of the radial displacement,contact force,frictional resistance and axial force of the string along with the well depth.Then a orthogonal test was designed to analyze the four factors of perforating pulse peak load,pipe diameter,pipe string collapsing strength,impact time influence the maximum stress of tubing string.