Genetic, Mechanics and Diagenetic Analysis of Faults Compartmentalization in Abu Dhabi, UAE
Despite considerable studies over the last two decades on the origin of faults and fractures and their diagenetic events in Abu Dhabi reservoirs, the debate about timing and mechanisms of compartmentalization of faults and their impact on reservoir-quality need to be better reconnoitered. A well drilled into a compartmentalized reservoir may see only part of the hydrocarbon in place over the production time scale. The barrier to free flow can be sealing faults, fault baffles, pinching out layers, overpressure zones, dense zones and/or low permeability zones. The combined use of all available well data, seismic, outcrops and fluid data to creating a geomechanics model is important to be able to apply a comprehensive approach to identifying and quantifying compartmentalization. This includes the analysis of fault distributions based on downhole measurements and 3D seismic fault identification techniques. Using this integrated study approach in some cases of Abu Dhabi fields will give a more meaningful and holistic picture of parameters controlling the spatial and temporal distribution of reservoir quality. The results in identifying the value of compartmentalization detection, let’s classifying into fault-dominated, stratigraphic, and mixed-mode compartmentalization. The presence of salt and shales will also be adding an important type, as the faults evolved, the leakage triggered the salt and shale to fill transferring them to sealed. Abu Dhabi reservoirs showing five major fault sets (N75W, N45W, N15W to NS, N30E and N60E) evolved through the tectonic history. These sets are evolved/reactivated strike-slip regime, which favors transtensional relations encouraging of the opening mode deformation zones triggered shale and salt to fill-in. The arrangement of these fault sets and the sense of overstep between them suggest that they have opposite senses of offset. The N45°W trending set shows evidence of sinistral shear, whereas the N75°W trending set shows dextral sense of offset. The transpressional zones creates mainly shearing deformation zones, which are less impacted by salt/shale intrusions, but shearing strain strength will consider the behavior of the accompanied faults. The Geomechanics model showed that these faults with high ratios of shear-to-normal stress resolved on their surfaces are critically stressed and likely to be active in the current stress field. As a result, these fault planes tend to have increased permeability and are likely to be conductive. Faults and fractures with low ratios of shear to normal stress are less likely to leak, provided they also have the appropriate structural or compositional sealing potential. Field development plans and exploration relies to a major extent on the compartmentalization potential of specific fault systems in Abu Dhabi. Knowing whether the hydrocarbons are contained in one or multiple compartments, is critical in determining project economic superiorities.
AAPG Datapages/Search and Discovery Article #90370 ©2020 AAPG Middle East Region Geoscience Technology Workshop, 3rd Edition Carbonate Reservoirs of the Middle East, Abu Dhabi, UAE, January 28-29, 2020