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Matthieu Deville de Periere¹; Aurelie Bonin¹,; Prabir Kumar Nath², Sunil Kumar²; Afrah Saleh Al-Ajmi², Jesal Hirani¹,Arun Dey²

1. Badley Ashton and Associates Ltd, Winceby House - Winceby, Horncastle, LN9 6PB - United Kingdom.
2. Kuwait oil Company (KOC) Exploration Group, PO Box 9758, Ahmadi 61008, Kuwait.

The Lower Cretaceous Minagish Formation forms one of the most prolific oil reservoirs in onshore Kuwait. As part of a multiwell study investigating the Middle and Upper Minagish Members, this work focuses on understanding the variations of porosity and permeability and assessing the extent of potential sweet spots in the unexplored south-western area of Kuwait. 

The sedimentological analysis interpret the Minagish sediments to be deposited in an intertidal to proximal mid-ramp setting, with the development of oolitic shoal corridor and sand bars formed in a more landward position on the inner ramp. The hydrocarbon stain is present where internal carbonate sand bar/intertidal deposits sit below an exposure above which a distinct change in deposition from clean carbonates to clay/organic matter-prone deposits (Upper Minagish) occurs. The well correlation shows a condensation of the sand bars/intertidal deposits in the south-western part of the area as a result of a progressive decrease in accommodation at the end of the regression, amplified in the landward position of the system. Amongst the various diagenetic phases that have been identified within the cored Minagish, the main cementation phases include synsedimentary marine fibrous calcite, equant to blocky calcite potentially formed by meteoric fluids and saddle dolomite formed within the burial environment. An early dissolution phase is observed throughout the stratigraphy, creating secondary macropores. A late dissolution phase is also likely to occur due to corrosive burial fluids.

Porosity and permeability are closely related to sedimentological variations: better reservoir potential is hosted within initially macroporous, coarse-grained peloidal and oolitic deposits (creating sweet spots), and the lower reservoir quality is associated with micritic-rich facies. Subsequent diagenesis locally influences the pore system evolution: the early mechanical compaction reduces the primary interparticle macropore volume and pore-throat radii in the grainy textures. The development of fibrous calcite cements within these units is likely to limit the negative impact of compaction on the pore volume, while pore-filling calcite and dolomite phases partially to locally completely occlude the macropore volume. The early dissolution event results in the creation of secondary interparticle, vuggy and mouldic macropores, while it possibly enhances the matrix-hosted microporosity of the micrite-rich deposits. However, in the grainy textures, the effect of this dissolution phase is minor and may potentially enhance the interparticle macropore volume. Since the sedimentary fabric plays a significant role on porosity and permeability as well as the relative influence of subsequent diagenesis, the sedimentary framework can be used as a direct platform for the reservoir architecture and prediction within the studied area.