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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

Where Is My Sand Wedge? Part 1: Exploring for Stratigraphic Trapping Potential in the Unayzah Group, South Rub' Al Khali Basin

Geoff Pike1; Craig Harvey1; Michael Hulver1; Ashraf Khalil1; Pieter van Mastrigt1

(1) South Rub Al Khali Company Ltd, Al-Khobar, Saudi Arabia.

The South Rub ‘al Khali Company Ltd is an Incorporated Joint Venture between Shell Saudi Ventures Limited (50%) and Saudi Arabian Oil Company (50%) and was set up in order to explore for non-associated gas in the South Rub ‘al Khali Basin as part of the Natural Gas Initiative in the Kingdom of Saudi Arabia.

To date exploration for a working Palaeozoic petroleum system has proven reservoir in 4-way structural dip closure and the presence of mature source rock. The search for gas is focused on the subtle, off-structure stratigraphic potential of the Unayzah Group, and in particular the Nuayyim Formation and/or Jawb Member sandstones.

The Unayzah Group is subdivided into Juwayl and overlying Nuayyim formations. The Juwayl Formation comprises a lower Ghazal Member, equivalent to the Al Khlata Formation in Oman, and an upper Jawb Member. Respectively, these contain the Unayzah C & B Reservoir Units. The Ghazal Member infilled palaeo-topography with glacio-fluvial outwash braidplain, cold aeolian dune, lacustrine, and braid delta facies. The Jawb Member is coeval to the upper Al Khlata Formation and to the Rahab Shales of Oman and begins with ice advance deposits (diamictites) that grade upward into glacio-lacustrine sediments characterized by debris flow diamictites, lake shoreface sandstones, turbidites, and finally by laminated mudrocks with dropstones. The Early-Middle Permian Nuayyim Formation (containing the Unayzah A Reservoir Unit) is coeval with the Lower Gharif & Haushi Limestone of Oman and comprises Wudayhi and overlying Tinat members. The Tinat Member comprises ephemeral/playa lakes, alluvial plain, and aeolian (dune, interdune, and sheet sand facies) deposits with time-equivalent fluvial (wadi) deposits along the basin margin. The depositional model is a dryland basin model, characterized by seasonal river flow and flood-drought cycles.

Prospectivity within the southern Rub ‘al Khali Basin comprises conventional 4-way structural dip closures as well as stratigraphic traps on the flanks of Permian structures. These stratigraphic traps may be very common and are under-explored. This presentation will combine geological models with seismic evidence to define the exploration potential of the Unayzah Group in the South Rub ‘al Khali Basin.