Stratigraphic and regional distribution of fractures in Barremian–Aptian carbonate rocks of Eastern Oman: outcrop data and their extrapolation to Interior Oman hydrocarbon reservoirs

Abstract

The carbonates of the Barremian to Aptian Qishn Formation are outcrop equivalents to major hydrocarbon reservoirs in the Middle East and in Oman specifically. The rocks are exposed in the Haushi–Huqf area of eastern Oman where they are affected by pervasive jointing and localized folding and faulting. Information gathered in the Huqf outcrops can be used to formulate predictions on fracture patterns in adjacent reservoirs. Systematic joints are confined to few meters-thick intervals of widely differing lithologies, which can be correlated over hundreds of square kilometers. Over the entire area, systematic joints are typically more than tens of meters long, have spacings of 4–18 cm and homogeneous morphologies. These joints are interpreted to be of Late Aptian age. The dominant set of joints strikes consistently NW–SE and developed parallel to the causative maximum horizontal compression SH. The direction of compression is at an high angle to the two major tectonic domains of the region, the subsiding Oman Interior basins and the elevated Haushi-Huqf High. NW–SE compression is proposed to have caused crustal/lithospheric buckling and thereby to have controlled Jurassic to Early Tertiary patterns of vertical movements. In such a scenario, the direction of compression is predicted to be constant over the entire domain. It is thus expected that Qishn carbonates in the subsiding Oman Interior basins also experienced NW–SE compression and developed systematic joints similar to those observed in the Huqf region. In the Neogene, with the establishment of the “Zagros” stress field, the maximum horizontal compression became roughly N–S, thereby possibly leading to the closure of pre-existing joint systems.