An Advanced 3D Geomechanical Forward Modelling Technique to Predict Sub-Seismic Fault Distribution in a Giant Oilfield, Offshore Abu Dhabi

ABSTRACT: Understanding the distribution of natural fractures is important for reservoir modelling to reproduce production history and for drilling operation to optimize well trajectory and required mud weight. The present study sought to model spatial distribution of sub-seismic faults developed by sedimentation, updoming and regional tectonic activities experienced in a giant oilfield, offshore Abu Dhabi. The study applied finite element analysis to reproduce the present-day geological structure in the field. Paleo-formation surfaces were created by using 3D structural restoration. A 3D geomechanical forward modelling simulated the evolution of geological structure from the time of deposition to the present day through sequential sedimentation process. The numerical simulation results appropriately reproduced the seismic structure from the viewpoint of geometry of dome structure and thickness of each formation. The distribution of rock strain by the simulation showed good agreement with the location of the seismic faults. The orientation of the fractures estimated in the simulation also showed good agreement with that of the fractures interpreted by borehole wall image log. The 3D geomechanical numerical simulation presented in this study significantly contributes on predicting the areas in which the fractures are likely to develop in response to the evolution of geological structure. 1. INTRODUCTION In development of oil and gas reservoirs, understanding of the spatial distribution of natural fractures makes a significant contribution to reservoir modelling to reproduce hydrocarbon production history. Prediction of the fractured areas is also important to optimize well trajectory and required mud weight to avoid excessive mud loss or kick in drilling operation. Additionally, in carbon dioxide capture and storage (CCS) projects, the distribution of natural fracture network in the not only reservoir but also caprock is one of the key issues to prevent unexpected migration of CO2 injected and to ensure the containment. The extent and network pattern of faults in the subsurface is interpreted and mapped by 3D seismic reflection imagery. Although sub-seismic faults and fractures below the limit of seismic resolution are interpreted by borehole image log, it is not always straightforward to evaluate the spatial distribution between the boreholes.