Structural Design and Parametric Study on Novel Carbon Fiber‐Reinforced Bismaleimide Composite Tubing and Its Embedded Joint for Shallow Wellbores

In this study, taking the service requirements of an 8000 m, 150°C, and 100 MPa ultra‐deep wellbore as the theoretical design target, a novel carbon fiber‐reinforced bismaleimide (CFRB) composite tubing was designed by using Classical Lamination Theory and the Tsai‐Wu failure criterion. The fiber winding angle, ply ratio, and number of layers were determined while ensuring manufacturability. The final tubing with a laminate structure of [±85°/±20°/±85°] 11 was determined via finite element analysis (FEA) to withstand combined axial tension of 660 kN and internal pressure of 110 MPa. However, the experimentally measured mechanical properties of the final tubing product reveal that the allowable external collapse load and internal pressure should be limited to 16 kN and 30 MPa, respectively, restricting its applicable well depth to within 1090 m. A P110 metal joint with both threaded and embedded connection capabilities was designed and fabricated to facilitate the installation of the developed CFRB tubing into the in‐service P110 tubing system. Equivalent stress‐strain analysis and tensile tests demonstrate that the P110 embedded joint exhibits reliable connectivity and excellent mechanical properties when coupled with the CFRB tubing, with the maximum tensile force of 843 kN at the connection between the two components.