Sequence stratigraphic controls on the gas-reservoirs distribution and characterization along the Messinian Abu Madi incision, Nile Delta Basin

Abstract

The Abu Madi sandstones represent the largest gas-bearing reservoirs in Nile Delta Basin of Egypt. This paper aims to perform a sequence stratigraphic analysis besides petrophysical appraisal for the Abu Madi Formation along the Messinian incised valley. Eight facies types (F1–F8) are identified in the Abu Madi Formation, ranging in lithology from sandstone, siltstone, shale and mudstone with different sedimentary structures trough/planar cross-bedding, ripple laminated/laminated and massive. The sequence stratigraphic analysis for thirteen wells extends in both offshore and onshore parts of this incision revealed that the Abu Madi Formation is divided into two depositional sequences: LMDSQ-1 (lower Abu Madi) and LMDSQ-2 (upper Abu Madi). The findings of the petrophysical assessment exhibit that the favorable gas intervals in each depositional sequence correspond the sandstones of the lowstand systems tract (shale content: 4–22%; effective porosity: 12–27%; water saturation: 20–63%) rather than the highstand systems tract or the transgressive systems tract (shale content: 5–30%; effective porosity: 7–20%; water saturation: 30 and 53%). The entire sandstones of the LSTs comprise four reservoir rock types: trough/planar cross-bedded sandstones (Type-1, F1), parallel-laminated sandstones (Type-2, F2), massive sandstones (Type-3, F5) and ripple cross laminated sandstone/siltstones (Type-4, F3). The massive sandstone (Type-3) is the best reservoir type since it contains interparticle pores with porosity up to 26% and horizontal permeability varies between 460 mD and 1439.37 mD. However, the ripple cross laminated sandstone/siltstones (Type-4) have the worst reservoir type, with an average porosity of 12% and a permeability of 0.6 mD.