Buckling of composite Cable: Simulation and physical testing of buckling of the composite cable inintervention operations within a production tubing
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Recent advances in drilling technology have enabled wells reaching up to 10 km and beyond. Conventional intervention technology has limitations when reaching into the high deviated and long horizontal sections of these extended reach wells. This thesis presents a new type of material and technique that has been introduced to intervention applications the latest years - the composite intervention cable. The composite cable is lighter than the conventional steel wireline and has a higher strength, stiffness and electrical current transfer capability. One of the main benefits of the composite intervention cable is the high stiffness of the composite material, allowing a surface injector head to push the cable into the well and thereby eliminate the necessity of a well tractor. However, pushing the composite cable into the high deviated and long horizontal wells will cause helical buckling and lock-up. Axial oscillations and vibration can effectively reduce the friction forces that arise between the locked cable and the inner wall of the production pipe. Analyzing and testing the use of a vibration tool together with the composite intervention cable are therefore one of the main objectives of the thesis. To investigate the forces and stress involved in pushing the composite cable into a well and to further test the concept of using a vibration tool, a practical test model has been built. The results were used to address the advantages and limitations of the cable and the vibration tool and to utilize comparison with the simulation results. The test results show that the reach of the composite cable is limited by the friction forces that arise between the compressed cable and the inner wall of the production tubing. Therefore, lock-up should be set as the dimensional maximum axial force that could be applied to the cable. Further it is proven that axial vibration reduces the friction force between a locked cable and the inner wall of the production pipe. This permits a higher axial force to be transmitted through the system before lock-up again is reached. However, it is unlikely that the vibration tool alone is suffiecient to implement the use of a injector head to push the cable and PLT into the challenging highly deviated and horizointal wells. An advance in vibration technology and further development of well-tractors and injector heads could implement the composite intervention cable to help increase the recovery rate and further follow up latest advance in extended reach drilling, even into complex ultra-long wells.