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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

Paleozoic Clastic Systems, Reservoir Quality, and Play Mapping in the Rub’ Al Khali Basin, Kingdom of Saudi Arabia

Michael Hulver1; Abdul-Hameed Azzouni1; Craig Harvey1

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

The South Rub ‘al Khali Company Ltd (SRAK) 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.

Initial exploration efforts by SRAK in their Contract Area 2 (southwest Rub’ al Khali) were focused on assessing the likelihood of a working Paleozoic hydrocarbon system using a regional grid of legacy and newly acquired 2D seismic data, geologic data from offset wells, and basin modeling results based on regional trends. Three wells drilled by SRAK in 2006-07 established the presence of source rock in the Silurian Qusaiba Hot Shale, reservoir in the Sarah Formation and Unayzah Group, and charge/migration in gas micro-shows from a mature Silurian source rock kitchen. Continuing seismic acquisition has enabled SRAK to identify a portfolio of structural closures and stratigraphic traps, and enhanced seismic processing has highlighted areas with acoustic properties consistent with porous rock and hydrocarbon accumulations.

Post-drilling analysis of geologic data and enhanced study of offset wells, has enabled SRAK to more thoroughly evaluate plays and prospects and their probability of success, as well as develop strategies for drilling and testing the sometimes fairly tight Paleozoic reservoirs. For example, reservoir quality of the glacial Late Ordovician Sarah Formation was found not to be entirely related to depth-of-burial, but also enhanced by clay coatings or degraded by clay matrix content. These factors are related to primary depositional environment: mixed marine-terrestrial systems such as proximal deltas provide good reservoir, while purely terrestrial glacial tills or shallow shelf environments produce rocks with poor reservoir potential. Paleogeographically, good reservoir is to be expected between the most distal and most proximal facies. Stratigraphically, the best reservoir to be cored and tested is expected in the middle Sarah, where glacial/interglacial and marine/non-marine transitions occur between glacial maxima normally observed at the top and bottom of the glacial succession.

Integrating data and applying a structured approach to exploration means SRAK assess opportunities from a play based not prospect based perspective and this allows linkage independent geological play elements and portfolio polarization.