Integrity Analysis Of Premium Connection Based On Finite Element Method

With the development of petroleum exploration technology and increase of high temperature, high pressure and ultra deep well, the service environment of tubing become worse. The connections of tubing are the weakest position, and failures such as leaking, dropping out, breakage always occurred there. According to the reference, leakages of tubing, abnormal annulus pressure of tubing and casing, even failure of the well integrity always appears in the oil field. So, the sealing and connection ability of premium connections should be focused on.Many methods were adopted to analyze the integrity of the premium connection. The analytical method is complicated and ignores the variation of contact stress along the tooth surface, the result is not accurate. The failure of thread occurs instantaneously, and the time-varying strain can not be sampled correspondingly, so there are also some limitations of full scale test method. Two-dimensional finite element models of premium connections, where the connections were simplified as an axisymmetric model, can not be used to analyze the circumferential stress. Therefore, three-dimensional finite element models of the premium connections were established in Abaqus, the process of making up was simulated to analyze the stresses when the torque are minimum, optimum and maximum. Also, the stresses of the premium connections exerted by axial force, internal pressure and the bending moment were analyzed.Some conclusions could be drawn from above research. The best sealing and connection ability of premium connections can be obtained when the torque is the optimum torque. Compared with only internal pressure, the sealing ability of the premium connections is better when both internal and external pressure existing, no matter the axial load is tensile load or compression load. In pressure test, without damaging the structure of the premium connection, the pressure should be controlled smaller than the burst strength,90% is recommended. The stress of premium connection is uniform when there are bending moments, which seriously influence the sealing of the premium connections. The results can be used to establish the relationship between the sealing ability and connection ability of premium connection and torque, axial load, pressure, bending moment. Also, based on the research, a large range of torque sensor with fast loading structure was manufactured, which effectively solve the problem of torque calibration and the torque control error.