Fault Planes Materials Fill Characteristics, UAE

Abstract

Abu Dhabi subsurface fault populations triggered basin system in diverse directions, because of their significant role as fluid pathways. Studying fault infill materials, fault geometries, zone architecture and sealing properties from outcrops as analogues to the subsurface of Abu Dhabi, and combining these with well data and cores are the main objectives of this paper. The fault core around the fault plane and in areas of overlap between fault segments and around the fault tip include slip surfaces and deformed rocks such as fault gouge, breccia, and lenses of host rock, shale smear, salt flux and diagenetic features. Structural geometry of the fault zone architecture and fault plane infill is mainly based on the competency contrast of the materials, that are behaving in ductile or in a brittle manner, which are distributed in the subsurface of Abu Dhabi sedimentary sequences with variable thicknesses. Brittleness is producing lenses, breccia and gouge, while, ductile intervals (principally shales and salt), evolved in smear and flux. The fault and fractures are behaving in a sealy or leaky ways is mainly dependent on the percentage of these materials in the fault deformation zone. The reservoir sections distancing from shale and salt layers are affected by diagenetic impact of the carbonates filling fault zones by recrystallized calcite and dolomite. Musandam area, Ras Al Khaima (RAK), and Jabal Hafit (JH) on the northeast- and eastern-side of the UAE represents good surface analogues for studying fault materials infill characteristics. To approach this, several samples, picked from fault planes, were analysed. NW-trending faults system show more dominant calcite, dolomite, anhydrites and those closer to salt and shale intervals are showing smearing of the ductile infill. The other linked segments and transfer faults of other directions are represented by a lesser percentage of infill. In areas of gravitational tectonics, the decollement ductile interval is intruded in differently oriented open fractures. The studied outcrops of the offshore salt islands and onshore Jabal Al Dhanna (JD) showing salt flux in the surrounding layers that intruded by the salt. The fractures and faults of the surrounding layers and the embedment insoluble layers are highly deformed and showing nearly total seal. As the salt behaving in an isotropic manner, the deformation can be measured clearly by its impact on the surrounding and embedment's insoluble rocks. The faults/fractures behaviour is vicious in migrating hydrocarbons, production enhancement and hydraulic fracturing propagation.