Sedimentology and play potential of the late Neoproterozoic Buah Carbonates of Oman

Abstract

ABSTRACT The search for new exploration plays in Oman, and recent successes in the Ara Group, has rejuvenated the interest of Petroleum Development Oman (PDO) in the stratigraphy of the pre-Ara Group. Below the Ara Group, the late Neoproterozoic Nafun Group comprises five formations. The Buah is the youngest of these formations, and represents the most promising exploration target. Accordingly, an integrated outcrop and subsurface study was initiated to better understand the distribution of the Buah depositional facies. High-resolution chemostratigraphy and field gamma-ray surveys were used to correlate outcrop data with the PDO subsurface database. These studies resulted in the reconstruction, with an unprecedented accuracy, of the distribution of the depositional environments at Buah time throughout Oman. This study indicates that the Buah was deposited on a distally-steepened carbonate ramp, during a highstand systems tract, as a shallowing and upward-coarsening cycle. Good reservoir facies (peloidal-ooidal grainstones) are ubiquitous in the shallow-water Buah sections, making up continuous sheets for tens of kilometers. Karst and fracture development at the top of the Buah may improve the reservoir quality, as in the case of the Makarem gas field in Oman. Buah reservoirs are generally capped by the Ara salt, except on structural highs where the top seal is provided by mudstones of the middle Haima Supergroup. The Buah off-ramp basinal facies represent potential source rocks with total organic carbon values ranging from 2.5–3.5 %.