Research on the sealing performance and lubrication characteristics of combined seal rings under extreme downhole completion production conditions

Purpose As the core execution unit of intelligent well completion systems, the flow control valve’s sealing structure faces multiple challenges under extreme drilling conditions. This study aims to focus on a combined seal ring, comprehensively using finite element analysis and thermal elastohydrodynamic lubrication (TEHL) theory to investigate the sealing performance and lubrication characteristics under extreme conditions. Design/methodology/approach First, the influence of fluid pressure and sliding wear on Mises stress and the contact stress of the primary sealing surface is analyzed based on finite element methods. Second, a mixed TEHL model is established and numerical calculations are performed to reveal the sealing performance and lubrication characteristics in the sealing region. Findings The results indicate that as fluid pressure increases, the contact pressure on the primary sealing surface rises significantly, the net leakage rate decreases, but the friction force increases linearly. Sliding wear reduces the interfacial contact stress and increases oil film thickness, leading to increased seal leakage and decreased friction. The sealing interface remains in a mixed lubrication state throughout, with the sealing conformity during the downstroke being superior to that of the upstroke. The region of minimum film thickness is prone to heat accumulation and lubrication deterioration. Research limitations/implications The limitations of this study are as follows: First, the finite element analysis only considered fluid pressure and sliding wear, without incorporating time-dependent effects such as temperature variation and stress relaxation. Second, the wear model adopted a constant wear coefficient, failing to reflect the dynamic evolution of the wear process. Finally, the experimental validation was conducted only within a low-pressure range of 0–4 MPa, which does not fully cover extreme high-pressure drilling conditions. Practical implications Enhance the reliability and service life of downhole flow control valve seals: reveal the contradiction that increasing pressure suppresses leakage but aggravates friction and wear, providing a balance point for sealing structure optimization; clarify the pattern that wear increases leakage while reducing friction, supporting wear-compensation design; the thermal-elastohydrodynamic model enables multi-field coupled analysis, predicts leakage and wear under high-temperature and high-pressure conditions, guides the material selection and structural design of seal rings and reduces drilling operation failure rates and maintenance costs. Social implications The research outcomes can enhance the sealing reliability of intelligent well completion systems under extreme drilling conditions, effectively reducing oil and gas leakage and production stoppage risks caused by sealing failures of downhole flow control valves. By optimizing the sealing structure and lubrication performance, it helps improve the exploitation efficiency of oil and gas resources, reduce unplanned maintenance and environmental pollution, ensure the stability and security of the energy supply chain and promote the development of the petroleum industry toward high efficiency and low risk. Originality/value This study integrates finite element analysis with TEHL theory to reveal the coupled effects of fluid pressure and sliding wear on combined seal rings under extreme drilling conditions. It establishes a mixed lubrication model incorporating viscous shear heating, asperity frictional heat and interfacial wear evolution. The predicted leakage and friction agree well with experiments, offering theoretical guidance for optimizing downhole sealing structures and extending their service life.