High-resolution sequence stratigraphy and reservoir characterization of Upper Lekhwair (Lower Cretaceous) reservoir units of a giant Abu Dhabi oil field

An extensive core-based sedimentological and high-resolution sequence stratigraphic study has been carried out on two Upper Lekhwair (Thamama Group, Barremian) Reservoir Units (ULRU1 and ULRU2) of a giant oil field onshore Abu Dhabi, with the aim of improving our understanding of the reservoir architecture. ULRU1 and ULRU2 are part of the highstand systems tract (HST) of a third-order depositional sequence, and are interpreted to represent two fourth-order parasequence sets built by eight fifth-order parasequences. ULRU1 and the underlying dense zone consists of burrowed, organic-rich, stylolitized, wispy laminated, packstones with echinoderms, shallowing-upward into wackestones, packstones and grainstones with rare rudists, foraminifera, peloids, and intraclasts. ULRU1 together with the underlying dense zone forms one parasequence set built by four parasequences. ULRU2 and the underlying dense zone consists of burrowed, organic-rich, stylolitized, wispy laminated skeletal wackestones and packstones, coarsening-upwards to grain-dominated, rudist-rich packstones, grainstones, floatstones, and rudstones. Like ULRU1, the reservoir facies of ULRU2 together with the underlying dense zone forms one parasequence set built by four parasequences. Best reservoir quality is developed in ULRU2 (permeability exceeds 1.0 Darcy), corresponding to rudist-rich, grain-dominated lithofacies representing laterally discontinuous shoals. Porosity and permeability trends follow the established high-frequency sequence stratigraphic framework. Our newly developed sequence stratigraphy-based geological (static) model improves prediction of flow behavior in ULRU1 and ULRU2.