oa Improved Understanding of the Athel Silicilyte through the Fara Formation: A Co-Eval Pre-Cambrian Analogue in the Sultanate of Oman

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