Advanced 3D Geomechanical Modelling of Seismic Fault Pattern Above the Crest Structure in a Giant Oilfield, Offshore Abu Dhabi

Abstract

Abstract Prediction of fault and fracture distribution is a key to incorporate enhancement of matrix permeability in reservoir modelling and to avoid excessive mud loss or kick in drilling engineering. The current study sought to model the fault pattern induced by updoming and regional tectonic activities in a giant oil field, offshore Abu Dhabi. The study applied finite element analysis to reproduce the present-day crest structure. The boundary conditions were applied by following updoming and regional tectonic lateral extension that the studied field has experienced simultaneously. The analysis calculated accumulation of rock strain and produced a discrete fracture network which corresponded with the magnitude of the rock strain. Mechanical anisotropy of rock mass due to the development of fractures was incorporated in subsequent numerical steps. The distribution of the rock strain was compared with location and pattern of fractures modelled by a clay-based analogue model at laboratory, seismic fault system and fractures acquired in the field. The distribution of rock strain by the numerical simulation showed good agreement with the major fracture pattern of the analogue model and seismic faults distribution which represent the northwest to southeast in the crest and the west-northwest to east southeast in the flank. In terms of the distribution of sub-seismic faults, the orientation of the fractures was evaluated by considering mechanism of shear-slip and tensile opening based on the stress tensor in each of the grid cells in the simulation. Shear fractures develop at oblique angle to the direction of the principal stresses based on the Mohr Coulomb criterion. Tensile fractures are orientated normal to the least principal stress. The orientation of the fractures estimated in the simulation also showed reasonable agreement with that of the fractures interpreted in the locations except for the near-top of the crest. The three-dimensional geomechanical numerical simulation presented in this study significantly aids the evaluation of the distribution of sub-seismic faults by combining the results of analogue model and seismic interpretation. The simulation technology presented has already been applied by combining with seismic interpretation for the purpose of prediction of the areas where fractures highly develop in the overburden intervals in the studied field.