Safety Analysis Of Casing Load And Strength In Salt-Salted Rock Formation

The rock in the salt-salt stratum has typical rheological properties,and the plastic deformation of the surrounding rock causes the external load of the wellbore to change,threatening the strength and safety of the casing.Therefore,the analysis of casing load and strength safety in salt-salt rock formation provides a basis for casing program design and subsequent construction parameter control,which has practical significance.Considering the change of ground stress caused by the rheological properties of rock,a series damper is used to describe the rheological characteristics of the rock based on the traditional model of the western original body,and a new model that can reflect the rheological properties of the rock is constructed.The rheological constitutive equation of rock uses the mathematical limit method to judge the accuracy of the equation,and the finite difference method is used to simulate the ground stress to verify the equation.Based on the rheological constitutive equation,the additional stress of the casing in the salt-salt formation is obtained.Considering the dog's leg,temperature,pressure,fluid density and viscosity,the stress of the casing in the salt formation is analyzed under the injection condition.The equivalent stress of the casing before and after the rheological transformation is obtained,and the bearing capacity of the casing before and after the rheological transformation is analyzed.The three-dimensional finite element model of casing-cement ring-stratum is established,and the casing in the salt-salt formation is analyzed.The stress intensity safety,by changing the model characteristics and mechanical parameters,simulates the casing stress distribution law when the wellbore is defective.The results show that the calculated maximum and minimum geostress results of the rheological constitutive equation and the ground stress formula are 6%and 1.65%,respectively.The equivalent stress acting on the casing after the formation rheology averaged 13.94%higher than that before the rheology.The greater the elastic modulus of the cement ring,the higher the protection effect on the casing;the casing is prone to flattening when it is not centered;when the circumferential opening of the cement ring defect is 66°,the stress on the casing is the largest;The inner wall defect of the ring has a greater influence on the strength of the casing than the outer wall defect.This study provides a basis for the method of obtaining the critical load of the casing in the salt-salt formation and the strength safety analysis of the casing.