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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

Biofacies and Palaeoenvironments of the Khuff C Carbonates in Southern Ghawar Field, Saudi Arabia

Geraint W. Hughes1

(1) Saudi Aramco, Dhahran, Saudi Arabia.

Semi-quantitative micropalaeontological analysis of closely-spaced core samples from the Upper Permian Khuff C carbonates in the Haradh area of southern Ghawar Field has revealed rich and diverse foraminiferal assemblages and associated microfossils, including bryozoa, calcareous algae, brachiopods, echinoids, ostracods, rare sponge spicules and cyanobacterial sheaths. The foraminifera are typically very small and include agglutinated, microgranular, miliolid and calcareous hyaline forms that display a variety of morphotypes that assist to refine the depositional environment. In addition to the considerable biofacies variations in ascending stratigraphic order within individual wells, lateral variations are present that together reveal regional and temporal palaeoenvironmental changes. These changes can be related to successive transgressive - regressive depositional cycles that compare readily with the distribution of porosity. Rock fabrics range from dense mudstones through wackestones, peloidal packstones to ooid grainstones. Porosity types encountered within the Khuff C reservoir include interparticle, mouldic and intercrystal. Diagenetic alteration of the primary fabrics includes cementation by calcite, dolomite and anhydrite, of which pervasive dolomitization is responsible for creating porosity within otherwise non-porous carbonates. The close association between biofacies and reservoir porosity distribution has led to the recent application of rigsite micropalaeontological analysis to biosteer under-balanced coiled-tube development drilling of the Khuff C reservoirs.