3D Modeling of Stability of Mobile Jack-Up Rigs Under Seismic Impacts

Abstract

The work is devoted to the study of the influence of external mechanical impacts on the stability of jack-up floating drilling rigs. Ensuring safety when working on jack-up floating drilling rigs (jack-up rigs) is one of the most important tasks at the initial stages of offshore hydrocarbon field development. The aim of the work is simulation of the stability of the rigs, which is in the operating mode, both in the absence of external effects acting on it, and when it is affected by various geodynamic processes. Calculation of jack-up rig stability in sea soil with complex viscoelastoplastic rheology under external mechanical influences was carried out using the finite element method. As a result of the work, the spatial distributions of stress and strain fields were determined both in the jack-up rig itself and in the area of the soil in the vicinity of its supports, in an equilibrium and disturbed state. The results of equilibrium static calculations made it possible to analyze the zones of localization of stresses and deformations in the jack-up rig with respect to stability: the structural elements that are most dangerous from the perspective of stability loss were identified. The analysis of the soil area in the vicinity of the jack-up rig supports made it possible to estimate the typical dimensions of the stress concentration zones arising during the jack-up installation and draw conclusions about the requirements on details and scalability of the model of mechanical properties needed for geomechanical modeling at specific objects. The obtained results of dynamic calculations - the response of theconsidered system to external influences simulating remote seismic processes - made it possible to study the process of loss of jack-up rig stability. The critical values of the parameters describing external influences were determined: in particular, the amplitudes of surface seismic waves leading to the loss of stability of the jack-up rig were found. The obtained results made it possible to formulate an algorithm for predicting seismic hazard during drilling in offshore conditions, based on numerical modeling of mechanical processes at specific locations.