Integrated sedimentological and petrophysical rock-typing of the Messinian Abu Madi formation in South Batra gas field, onshore Nile Delta, Egypt

Abstract

Abstract The Messinian incised-valley fill (IVF) sediments of the Abu Madi Formation host the most prolific gas-bearing sandstones in the onshore Nile Delta, Egypt. This study provides the first integrated geological, geophysical and petrophysical approach in order to link the Abu Madi sandstones’ reservoir properties with their geological framework, and thereby optimize the predictability of the most prospective reservoir rock types (RRT). Sandstone-bearing reservoir levels are mostly associated with the fluvial-estuarine valley-fill sediments (Abu Madi levels II and III). The intergranular volume of some sandstones (e.g. arkoses) is occupied by compacted ductile argillaceous rock fragments (pseudomatrix), and therefore have dominantly microporosity with anisotropic, poorly-connected pore system. Three RRT were recognized in Abu Madi reservoir levels. RRTI has the best poro-perm characteristics with excellent capillary properties (e.g. megapores, lowest initial displacement pressure ∼10 psi air/mercury and irreducible water saturation Swir below 20%). Pore system heterogeneity increases in RRTII and RRTIII. The latter contains dominant micropores and exhibits the highest initial displacement pressure ∼500 psi air/mercury and Swir exceeding 50%. RRTI often comprises subarkoses associated with the cross-bedded, massive and cross-laminated lithofacies of the fluvial channel-fill and fluvial channel sand bars facies. Whilst RRTII and III mainly comprise the sandstone lithofacies deposited in the abandoned fluvial, estuarine and restricted marine successions. Excellent reservoir quality facies follows the depositional trend of the valley-fill fluvial channels and pinches-out where repeated avulsion and channel abandonment processes dominate. The spatial distribution of Abu Madi RRT highlights the paramount impact of syn-depositional attributes and canyon-floor relief on the sediments’ reservoir heterogeneity and productivity. Moreover, the present integrated RRT approach could serve as a model for exploration in analogues settings where autogenic processes induce widespread sedimentary heterogeneity, which largely impacts the reservoir quality.