According to the tubing string failure statistics in the oilfield, fatigue crack of tubing joint thread in high temperature high pressure (HTHP) ultradeep gas wells remains a problem because it can cause tubing strength degradation, tubing fracture failure, well workover, and even well abandonment. In order to obtain a better understanding of tubing thread fatigue and quantify the fatigue life of tubing joint thread in HTHP ultradeep wells, experimental study, elastic–plastic mechanical simulation, and multi-axial fatigue calculation are carried out in this paper. Based on the similarity theory, the vibration mechanical testing device of the tubing string is designed, and the multi-axial load of the tubing joint thread in the actual working condition is obtained. Meanwhile, tubing joint BX1 thread model is established with ansys software, and the stress distribution of tubing joint thread is analyzed on the boundary condition acquired from experiments of vibration test of tubing string. Finally, according to the multi-axial fatigue theory, the fatigue life prediction value of the tubing thread made of Super 13Cr110 and Super 15Cr125 is compared and analyzed. The work presented in this paper can provide theoretical method and technological basis for the study on the frequent failure mechanism of tubing joint thread in HTHP ultradeep gas wells.

To avoid the failure of mandrel-type casing hanger, this article provides a new type of metal sealing structure, and the sealing is achieved through plastic flow of soft metal and elastic deformation of matrix. A finite element analysis model for sealing performance of mandrel-type hanger is established to study the deformation and contact pressure of sealing cone. Among the four sealing structures studied in this article, the elliptic surface is the optimal. It is suggested to design smaller equal cone angle of inner cone angle (β) and outer cone angle (α) in the limited space as far as possible so as to obtain larger average contact pressure. These findings can provide references for the structural design of the seal area of the mandrel-type hanger. The sealing test results show that the sealing curve turns to be a straight line under water pressure and air pressure of 140 MPa. The results of theoretical study and laboratory experiment show that the sealing structure of full-metal multilevel conical elliptical surface is reliable and can meet the sealing requirements of the oil field wellhead device under limit working condition of 140 MPa.

It has been widely acknowledged that traditional packers will lose their elastic performance in the context of long periods of operation due to plastic deformation. This paper will introduce a swellable packer that can reduce the failure cases of production effectively. The deformation of the packer rubber in different media and temperatures has been analyzed. The pressure test of several packer rubber under different media is carried out in this paper. The reasonable expansion clearance between the rubber tube and the well wall is obtained by strength calculation to ensure the sealing reliability of the packer. Finally, the thermomechanical coupling calculation of the packer with different structural sizes is carried out. Experiments at different temperatures show that the higher saline concentration is associated with a lower expansion rate and a larger expansion rate in clear water. At the same time, the expansion of volume in clear water increases. In addition, the higher the external temperature is, the larger the temperature gradient is. When the temperature of the outer ring is between 100°C and 140°C, the internal temperature rises to 37°C under the thermomechanical coupling effect.