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7.5 Reservoir analogues

Outcrop models can be used as an analogue for a hydrocarbon producing reservoir. Several hydrocarbon
fields with similar geometry and/or lithology to the Favignana calcarenite complex can be found in the
literature. It is however difficult to make a thorough comparison with the field data from Favignana based
on publicly available literature, as a detailed description of the geology is often not provided. Usually
publications only give a general description of the reservoir rock, but this section is an attempt to present
potential reservoir analogues. Because the Middle East is the world’s most prolific carbonate reservoir
region, most of the reservoirs considered here will be in that area.

1. A very well known hydrocarbon producing unit in the Middle East is the Asmari limestone
(Alsharhan & Nairn, 1997), with fields like Ahwaz and Bibi Hakimeh in the Iranian Zagros foreland
basin. The foraminiferal wackestones and packstones from the Early Miocene are interpreted to
be deposited on a marine platform to -slope. The best producing intervals in an Asmari field are
however not the limestones, but interbedded sandstone units.

2. The Shaybah field in the Rub al Khali desert in Saudi Arabia consists of two units, of which the
upper part is interpreted as bioclastic calcarenites with rudists (Brown & Husseini, 1977). With
an average porosity of 0.23 — but a mean permeability of only 15 mD — the reservoir shows
characteristics of a carbonate reservoir. In many cases a high amount of pore space is present,
however connectivity is limited.

3. Qassim et al. (2003) discuss the Kharaib reservoir in Bahrain, consisting of three units that are
in some cases heterogeneous and therefore challenging to model. Like many fields in the Middle
East, the Kharaib is a carbonate reservoir, and is subdivided into three units. Core analysis showed
clean bioclastic packstone at the top of the Upper Kharaib member, which is interpreted as being
deposited on a high-energy ramp environment. Because deposition occurred above the storm wave
base, according to the authors some material has been transported by storm-related events.

4. Rao & Talukdar (1980) describe the petroleum geology of the Bombay high field, which is by far
the biggest oil field in India. The productive zones are interpreted as high amplitude, high velocity
and continuous facies with several transgressive and regressive periods. Some intervals contain high
amounts of benthonic foraminifera which are used in order to make biostratigraphical correlation.
No information on primary sedimentary structures is found.

5. The Raudhatain field in northern Kuwait consists of heterogeneous Mauddud carbonates (Azim
et al., 2003). These carbonates are interpreted as being deposited on a low angle ramp setting,
where the best reservoir quality can be found in the high-energy upper ramp grainstones. Deposition
of cross-bedded carbonates occurred in tidally influenced channels. Lower on the shelf, a transition
to wackestones — supported by a fine grained matrix — is observed.

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