An Assessment of Seal Ability of Tubing Threaded Connections: A Hybrid Empirical-Numerical Method

Oil and gas development has strict requirements for the seal ability of premium threaded connections (PTCs) of tubing. Assessing the seal ability of joints can help reduce the risk of leakage after running the string. Using experimental methods to investigate thread sealing capability is time-consuming and expensive, and furthermore, the results of the finite element simulations are not accurate enough. To better address this issue, a hybrid method is utilized as an advanced solution: we establish a geometric nonlinear model and tie it to an empirical formula based on experimental data. With this method, we explore the variation of the seal ability of a PTC within the actual working load range. Our results indicate that the increase in internal pressure increases the contact pressure on the contact path to a certain extent, but reduces the seal ability of the joint. Also, an increase in the axial tensile load will significantly impair the performance of the joint to seal. Eventually, an economic appraisal is obtained by considering the seal ability of different type of joints. The described workflow may be adopted in other wells to predict the potential string leak problems induced by premium threaded connections with cheap computational costs, and to compare the seal abilities of different PTCs for optimal purposes of saving drilling costs.