Abstract
The Pliocene Kafr El-Sheikh (KES) Formation in the onshore Nile Delta region hosts numerous shallow gas accumulations. These are readily detected on seismic profiles by definable direct hydrocarbon indicators (DHI). However, the presence of residual gases causes many production failures. Two shallow (< 1500 m) pay zones were investigated in this study; both display seismic flat bright spots. The shallower pay zone (pay zone 1) comprises prograding distributary channel-fill sandstones, whereas the deeper pay zone 2 constitutes the transgressive distal sand bars. Pay zone 1 sandstones have better reservoir quality in terms of porosity (Av. 25.68%), permeability (86 md), water saturation (Av. 43.26%), and hence host thick gas accumulation (~ 15 m) with high net/gross (N/G) ratio ~ 0.98. On the other hand, pay zone 2 has a significant reservoir heterogeneity and contains only residual gases with N/G ratio of 0.26. The eodiagenetic infiltration of clays (Av. 31.46%), authigenic precipitation of glauconite (Av. 7%), and formation of pseudomatrix materials (Av. 2%) in pay zone 2 sandstones have the most detrimental impact on their reservoir quality. Elevated water saturation in pay zone 2 (Av. 64%) reduced the movable hydrocarbon content and results in accumulation of residual gases. Mild mechanical compaction preserved the intergranular porosity of the pay zone 1 sandstones, and incursion of meteoric water facilitated the dissolution of feldspars, the neoformation of secondary pore spaces (Av. 2.9%), and thus increased the reservoir storage and flow capacities. This study highlights that the initial depositional setting of the shallow siliciclastic reservoirs controls their diagenetic pathways and hence their reservoir quality.
Highlights
The Nile Delta was considered a minor hydrocarbon-bearing province where the exploration activities were confined to the Abu Madi valley network (Messinian) until the mid1990s
Exploring the Pliocene deep-water channel plays did not begin until the discovery of the giant offshore gas accumulations in Scarab, Saffron, and Simian fields by British Gas in 1998 and 1999 (Dolson et al 2005)
Thereafter, the exploration endeavors were mainly focused on the offshore Pliocene targets where the bulk of the Nile Delta basin resources lies in the Pliocene slope channels which form
Summary
The Nile Delta was considered a minor hydrocarbon-bearing province where the exploration activities were confined to the Abu Madi valley network (Messinian) until the mid1990s. In the Nile Delta onshore region (Fig. 1), the main hydrocarbon reservoirs are the Neogene-Quaternary siliciclastic successions which were deposited in a wide range of depositional environments (e.g., EGPC 1994; Dolson et al 2005; Leila et al 2015; Leila and Moscariello 2019). In this region, the Pliocene Kafr El-Sheikh (KES) Formation hosts the very potential shallow siliciclastic reservoirs which were deposited during and after the major marine transgression at the end of the Messinian salinity crisis (MSC) (Fig. 2) (Barber 1981; Said 1990; Garcia-Castellanos et al 2009).
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