Thermal Effects on Hydromechanical Response of Seabed-Supporting Hydrocarbon Pipelines

Abstract

Subsea pipelines are commonly used for transportation of hot hydrocarbons from offshore sites. The temperature difference between the hot pipeline and the cold seabed induces thermal loads. Temperature effects on the hydromechanical response of a seabed have been overlooked in the majority of previous studies. In this paper, a framework based on isogeometric analysis (IGA) is employed for fully coupled modeling of thermo-hydromechanical (THM) processes in saturated subsea soil subjected to harmonic hydraulic loading conditions. The latter enables the model to take into account the tide-induced pore pressure that is particularly important for design purposes. The proposed IGA-based model offers interelement connectivity and can benefit from a high-order degree of approximation in the simulation of nonlinear problems. Bézier extraction is used to integrate IGA with the finite-element method in the proposed framework. A two-dimensional model is used to investigate the seabed response during three phases: pipeline postinstallation (Phase 1), operation conditions (Phase 2), and shutdown period (Phase 3). Phase 1 represents the isothermal behavior of subsea soil during a short postinstallation period. Phase 2 corresponds to a relatively long nonisothermal operational period and Phase 3 simulates the nonisothermal behavior of seabed in the shutdown period. The results show the induced thermal gradient changes the horizontal deformations from negative to positive and vice versa during the long-term operational (Phase 2) and shutdown (Phase 3) periods, respectively. Incorporating the thermal effects into the simulation changes the seabed response from rotational mode in isothermal conditions to sliding mode in nonisothermal conditions.