The optimization of rubber core structures in rotary blowout preventers (RBOPs) to enhance sealing performance and fatigue life under cyclic stress is crucial for improving safety in oil and gas drilling operations. Researchers have undertaken a comprehensive study that addresses the performance of the conical rubber core in RBOPs, particularly in underbalanced drilling scenarios, where the mechanical stresses are significantly heightened due to the alternating passage of the drill pipe body and its joints.
As oil and gas exploration ventures into deeper and more complex geological formations, the integrity of blowout preventers is increasingly tested. The rubber core serves as a vital sealing component in these systems, responsible for preventing hazardous wellhead fluid overflow. However, due to repeated operational cycles and the associated fatigue, these rubber components are highly susceptible to failure. To mitigate potential blowout risks, researchers, including Lianglin Guo and Zhiqiang Huang, have focused on extending the life and improving the sealing performance of these rubber cores through structural optimization techniques.
The study employs various investigative methods, including finite element analysis and experimental assessments, to analyze the stress distributions within the rubber core during operations. By determining the material parameters through uniaxial tension and compression tests, the team was able to fit their findings to the Yeoh constitutive model, effectively expressing the stress-strain relationship characteristic of rubber under operational conditions.
In their dynamic sealing simulations, researchers discovered that the inner cylindrical surface of the rubber core bore the brunt of stress during operation, especially during transitional phrases when the drill pipe body and joint alternated. Initial tests indicated a peak stress value of 22.98 MPa and a stress amplitude of 5.14 MPa — figures that highlight the significant risk of fatigue cracking, which could compromise the sealing effectiveness of the core.
To systematically improve the sealing performance, a Plackett-Burman design methodology was employed to screen structural parameters affecting sealing pressures. The analysis revealed three critical parameters: cone angle, contraction angle, and inner diameter. This insight led to targeted sensitivity analysis, which solidified the need for comprehensive structural optimization to enhance performance durability.
The optimal structural design proposed includes a cone angle of 27.7°, a contraction angle of 68.2°, and an inner diameter of 82.1 mm. Post-optimization simulations indicated a reduction in peak Mises stress by 3.64 MPa and a decrease in stress amplitude by 39%. This reflects a substantial improvement, significantly lowering the risks associated with fatigue failure.
Notably, the verification of the study's predictions indicated a measurement error of only 0.42 MPa, further validating the effectiveness of their structural optimization model. As the authors of the article emphasized, "The peak value of Mises stress was reduced by 3.64 MPa, the amplitude of Mises stress was reduced by 39%, which validated the response surface prediction model." This finding underscores the promise of optimizing rubber core structures as a pathway to enhancing the safety of drilling operations.
As the oil and gas industry continues to explore deeper and more challenging environments, ensuring the reliability of drilling equipment becomes paramount. The research highlights the need for rigorous testing and optimization of critical components such as the rubber core in rotary blowout preventers. Preventing well control failures not only safeguards the equipment and economy but also protects the environment from disastrous spills and losses. Future research avenues may delve deeper into refining material properties or investigating multi-faceted interactions in rubber components to push the limits of operational safety further.
Through innovative application of statistical design methodologies and finite element modeling, this research sets a precedent for the enhancement of industrial safety standards in drilling processes, demonstrating a proactive approach to addressing the challenges posed by modern drilling operations.
