Controls of facies distribution on reservoir quality in the Messinian incised-valley fill Abu Madi Formation in Salma delta gas field, northeastern onshore Nile Delta, Egypt

Abstract

The Messinian incised-valley fill sediments “IVFs” of the Abu Madi Formation comprise the most prospective hydrocarbon-bearing reservoirs in the Nile Delta onshore and offshore. An integrated seismic-stratigraphic, sedimentological and petrophysical approach is applied to identify the factors controlling reservoir heterogeneity within the Abu Madi IVFs. Two separate channelized systems are interpreted and reflect the variation in flow dynamics and depositional energy. Morphologically, the channel system at the base constitutes the deeply-incised (average relief ∼ 80 ms “ms”) flat-filled channels corresponding to the braided fluvial pattern, whereas the channels at the top consists of shallower (average relief ∼ 20 ms) concave-up and shingled-filled channel facies of the meandering fluvial pattern. Coarse-grained quartzose sandstones are predominant in the channel sand bars, channel lags and channel-base drapes of the braided channel system. Higher in the section, the meandering fluvial facies hosts higher proportion of fine-grained sediments accumulated in the abandoned channels and their floodplains.The relative proportion of clays and pseudomatrix materials exercise the first-order control on the pore-scale heterogeneity and reservoir quality. Four reservoir rock types (RRT) were interpreted having different lithological and compositional characteristics and thereby petrophysical flow properties. Capillary pressure, irreducible water saturation, permeability anisotropy and pore-system heterogeneity increase from RRTI to RRTIV. RRTI intervals consist the quartzose sandstones preferentially accumulated at the base of the fining-upward cycles in the braided fluvial sediments. This study highlights the impact of sedimentological and compositional controls on the pore-scale heterogeneity, and therefore will enhance the predictive models for exploration in the incised-valley fill reservoirs.