Double-layer pipe dual-gradient drilling wellbore pressure calculation model and parameters optimization

Abstract

Deepwater oil and gas extraction face the problem of narrow safety density window, and double-layer pipe dual-gradient drilling is one of the effective ways to solve the problem of narrow safety density window, but the calculation model of borehole pressure and optimization method of drilling parameters for double-layer pipe dual-gradient drilling has not been thoroughly investigated. Based on the fluid dynamics theory, a dual-gradient drilling wellbore pressure calculation model was established, considering the influence of lift pump head size and installation location on the bottom hole pressure and the dynamic changes of wellbore pressure during drilling. Based on the wellbore pressure model and step-out strategy, the optimization model and algorithm of double-layer pipe dual-gradient drilling parameters were established with the minimum bottom hole pressure difference as the objective function and drilling fluid density, displacement, lift pump to bit distance and back pressure as the optimization parameters. Simulation analysis of the optimized drilling parameters (drilling fluid displacement and wellhead return pressure) was carried out using the optimization algorithm. It was found that the optimized drilling parameters could increase the drilling depth, reduce the bottom hole pressure differential and improve the mechanical drilling speed. The above optimization model and method can be used to optimize the drilling parameters for double-layer tubular dual-gradient drilling, which is beneficial to increase the drilling depth and reduce the bottom hole differential pressure.