Microstructural and Petrophysical Properties of Fault Rock from Outcrops in the United Arab Emirates

Abstract

Abstract There are many studies covering the RAK and Al-Ain area, but most of these studies focus on sedimentology, sequence stratigraphy and some structural events were conducted by ADNOC, ExxonMobil and PDO in the north of Oman. To date, no comprehensive field study of fault sealing has been conducted on these outcrops or in any place in the UAE. Fieldwork was undertaken in the valley/Wadi Rahabah, Wadi Al Bih and Jabal Hafit, which provides a good analogue for the fault in the Shuaiba, Thamama and Khuff reservoirs in the Abu Dhabi Onshore (OS) field. The results provided evidence that all fault rocks from outcrop exposures could act as conduits in the damage zone (DZ) and baffles in the Fault core (FC). The permeability contrast between fault and host within the reservoir suggest that all fault rocks from outcrop exposures could act as baffles in the DZ and seals in the FC. The FC is cut by open fractures, and thickness varies significantly over a short distance in the outcrop. If such fractures are present in the subsurface, they could allow the DZ to act as a conduit to flow and the fault could act as a baffle. The variation in the FC thickness ranges from 2 cm to 0.5 m within a short distance of around 10 m. In addition, the ranges span from 4 to 30 cm within a short distance of around 2 m from different outcrops, limiting the extent to which the FC can act as a seal. Three types of microstructural textures of FC were found in the UAE outcrops: first, a breccia located in the Jilh formation; second, a micrite-dominated located in the Khuff formation; and third, calcite cement located in the Shuaiba and Rus formation.