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Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Improved Understanding of the Athel Silicilyte through the Fara Formation: A Co-Eval Pre-Cambrian Analogue in the Sultanate of Oman
(1) Petroleum Engineering, Petroleum Development Oman, Muscat, Oman.
The Athel silicilyte represents a unique type of reservoir in the Sultanate of Oman with only two fields currently on production in the South Oman Salt basin under pressure depletion schemes. The next development for one of these fields will incorporate miscible gas injection where sweep efficiency, injectivity and rapid gas breakthrough are key uncertainties. Since the development of the field, the lack of an identified depositional analogue has limited the understanding of rock property distribution, the prediction of facies and potential reservoir extent that all impact these key uncertainties. However, examination of the Pre-Cambrian Fara Formation in Wadi Bani Awf provides a potential analogue for sediments with similar lithologies and age of deposition. Characterization of the Fara Formation and the extent to which it can be directly applied to the subsurface is the focus of our current research.
The screening of the Fara Formation as an analogue has involved detailed measuring of stratigraphic sections, acquisition of spectral gamma ray, petrography, bulk mineralogy and stable isotope analysis. Initial results indicate the Fara Formation and the Athel silicilyte were both deposited in an enclosed basin, starved of clastic input, under reducing conditions and below storm wave base. Both formations display laminated silicified sediments that indicate seasonality, deposition by traction and suspension and occurrence of microbial mats. Slumping and fine-grained turbidites are a commonality and reflect margin instability likely associated to ongoing tectonism. Petrographic and field examinations indicate dolomite cementation predated silicification and at least two phases of silicification have taken place in the Fara Formation. This has implications for the silica precipitation model. The large component of volcaniclastic material in the Fara Formation suggests that volcanic activity and basin configuration were key factors in the development of the Athel silicilyte during the Late Pre-Cambrian of the Sultanate of Oman. Unlike the Athel however, the Fara formation also shows a large proportion of carbonate and a diversity of lithofacies including fore-reef talus deposits, debris flows, turbidites, and redeposited laminated microbial boundstones that has not been recognized to date in the subsurface. This paper presents early results and potential implications for exploration and production of the Athel silicilyte.