GEOMECHANICS OF THE SOUTH FURIOUS FIELD - AN INTEGRATED APPROACH TOWARDS SOLVING COMPLEX STRUCTURAL GEOLOGICAL PROBLEMS, INCLUDING ANALOG AND FINITE-ELEMENT MODELING

The South Furious oil field, offshore Sabah (Malaisia), is an asymmetr ic anticline bounded on the steep southern flank by a series of steep E-W-striking reverse faults and affected by intense E-W crestal normal faulting immediately next to and contemporaneous with the reverse fau lts. In spite of the very good sand development and a high sand percen tage, the reservoir performance is very poor. A study was undertaken t o describe and understand the development and the mechanics of this ty pe of structure and to explain their presence in almost undisturbed se diments around them. The regional tectonic development was studied to provide a basis for a geological model of the structure. A structural geological model was necessary to be able to predict the type of fault s and fractures and their location in the structure. The proposed stru ctural development was modelled with analogue sandbox experiments and numerically simulated with a finite-element program (GEOFEP). The resu lts indicate that basement faulting related to the closing of the Sout h China Sea, induced differential sediment loading, triggering asymmet ric clay diapirism in the core of the anticline. The asymmetry resulte d in contemporaneous formation of steep reverse faults at the leading edge of the migrating anticline and normal faults in a crestal collaps e system. The reverse faults and associated shear fractures (as seen i n cores) have a sealing cataclastic fabric. This explains the severe c ompartmentalisation of the reservoir with consequently poor production behaviour, in particular in the reverse faulted part of the field.