Physical modelling of subsea structure removal via thermally induced pore pressure

Abstract

Given the requirements of environmental agencies, the decommissioning of subsea structures, including removal, recycling, restructuring or re-adaptation, is inherent to deepwater oil exploration activities. During removal by lifting, the possible development of negative excess pore pressure (i.e., suction) in the soil beneath the structure significantly hampers the recovery of subsea infrastructure. This study presents a method for potentially reducing this suction by heating the fine soil under the foundation during uplift to produce excess thermally-induced positive pore pressure, which may reduce or eliminate suction. Reduced-scale physical modelling studies of mudmat/skirted like foundation structures showed that the negative pore pressure generated during pullout was in certain amount counterbalanced by the thermally-induced positive pore pressure, facilitating their removal. However, this process depends on the magnitude of the sustained loading with respect to the pullout resistance. Upward displacements take place just after heating, without further load increments and the displacement rate is dependent on the level of sustained load.