Abstract
The main objective is to unravel the development of the fracture system within the hydrocarbon fields in the Onshore of Abu Dhabi, where an alternative understanding of the fracture system development in association with the counterclockwise rotation of the regional causative stress throughout the geologic time is introduced in this paper.
Manifestation of the tectonic history of Arabia in the UAE is demonstrated by both folding represented by gentle and open folds comprising most of Abu Dhabi's hydrocarbon structural traps and a brittle deformation represented by a fracture system comprising long en echelon seismic faults and several joint and vein sets. The most dominant, tens of kilometers long seismic faults in the Cretaceous rocks of Abu Dhabi are the N75W and N45W oriented faults, which have been considered so far as conjugate strike-slip faults. It is argued here whether these two seismic fault sets, which appear in many instances as conjugate sets, have been really developed coevally by a single tectonic event when the SHmax was approximately at 120°? The current understanding that these faults are strike-slip faults despite the absence of extensive horizontal displacements along them as shown on different time-slices is also discussed. Seismic attribute analysis and interpretation, outcrop analogs and fracture description from logs and FMIs reveal that this fracture system might have been developed in a more complicated manner than reported in different publications.
It is proposed here that the N75W seismic faults have been developed first as tensile fractures shortly prior to folding when SHmax oriented approximately at 120°. The N45W seismic faults have been developed at a later stage possibly as splay faults by reactivation/ branching from the preexisting N75W when the SHmax was approximately oriented E-W. This has occurred by a continuous counterclockwise rotation of the causative SHmax stress from Cretaceous to present. A periodic strike-slip movement along deep-seated basement faults could also have developed many structural features in the sedimentary cover including several hydrocarbon fields in the Onshore of Abu Dhabi.
The implications of the drift of the causative stress with geologic time from ∼120° to E-W, NE-SW and finally to NNE-SSW include its effect in reactivating the preexisting fracture system, tilting folds, and control fluid charge and movement within Abu Dhabi petroleum system. The significance of the results is the impact on exploration, production and field development plans. In the exploration of the new plays, both leads with their fractures can be predicted once the direction of the paleo-causative stress can be defined. In production and filed development planning, predicting the fracture system would help better production with appropriate well placement.
