Failure Mechanism And Experimental Study On Bonding Performance Of Set (Steel) Pipe-cement Stone Ring Interface

Interface cementation has always been a very popular research topic.Many scholars have done a lot of research on the failure mechanism of interface cementation.At the same time,the failure of interface cementation is the most difficult problem to control in engineering.In this paper,based on the background of sealing integrity in cementing engineering,theoretical analysis,experimental exploration and numerical simulation of cementing failure are carried out with casing-cement sheath interface cementation as the test object.There are two main aspects to study: one is from the radial interface cementation failure theory and the longitudinal interface cementation failure theory;the other is from the pure cementation strength,the diameter(normal)interface cementation failure and the longitudinal interface cementation failure mode without the normal force under the influence of other factors;the third is from the casing-cement annulus longitudinal cementation surface.Failure is numerically simulated.The main research contents are as follows:(1)The interfacial cementation failure is analyzed theoretically from the diameter(normal)to the longitudinal direction,and the failure principle of casing-cement-stone radial interfacial cementation is analyzed by using the thick-walled cylinder theory.The failure mechanics model of longitudinal cementation surface of sleeve(steel)pipe-cement-stone ring is established through the relevant interfacial shear failure theory.(2)Three small tests are carried out to investigate the interface cementation failure in two levels.Because the radial cementation failure of sleeve-cement-stone ring interface can't be studied directly in laboratory tests,the radial(normal)cementation failure is studied by direct tension test and four-point bending beam bending test.The results show that the bending test of four-point bending beam is better than the direct tension test.In the extension test,the bending test specimens of four-point bending beams belong to the pure bending section in the middle of load,and the interfacial fracture strength is the failure strength of interfacial bonding.In addition,the test results show that the interfacial bonding strength of bending beams is larger than the actual value.(3)Through the longitudinal cementing failure test of sleeve-cement sheath interface,three typical failure modes of interface cementing are presented in the test process.The first failure mode of interface cementation is that when the failure strength of interface cementation has not been reached,the cement-stone ring is destroyed first;the second is that after the failure of interface cementation is completed,the cement-stone ring is intact,the sleeve and the cement-stone ring slip relatively,and there is a certain amount of friction force,which verifies the sleeve-cement-stone ring interface established by the failure mechanics model of other two-phase interface cementation.Longitudinal cementation failure mechanics model;the third is that the interfacial cementation force is particularly large,and when the peak cementation load is reached,the interfacial cementation failure and the cement-stone ring are destroyed simultaneously.According to the three failure modes mentioned above,the results show that the strength values are as follows: the third interfacial cementation failure strength is more than the second interfacial cementation failure,as well as the first interfacial cementation failure.At the same time,it is pointed out that in order to ensure the success rate of the test,it is necessary to carry out the longitudinal cementing failure experiment of the sleeve(steel)pipe-cement-stone ring interface.(4)In order to further verify the integrity and accuracy of the test,it is better to combine the tests and carry out the numerical simulation of the failure of the longitudinal interface cementation of the sleeve(steel)pipe-cement stone ring.When the diameter(normal)force is not defined,the established mechanical model and the experimental research results show that the degree of coincidence is high,which verifies the perfect combination of the correctness of the mechanical model and the experimental implementation.