Print this pageAAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Mapping and Reevaluation of the Main Unayzah a Eolian Fairway, Southeast of Ghawar Field, Saudi Arabia: beyond the Porosity Sweet Spot
(1) Area Exploration, Saudi Aramco, Dhahran, Saudi Arabia.
The Lower Permian - Upper Carboniferous aged Unayzah Group encompasses some of the main Paleozoic reservoirs in Saudi Arabia. It constitutes one of the prime targets of Saudi Aramco’s exploration efforts in the Paleozoic section.
The upper reservoir interval, Unayzah A, is comprised of a series of fluvial, playa, lacustrian and eolian sandstones, which exhibit lateral variability.
The area southeast of the Ghawar field is characterized by a predominance of eolian sandstones that constitute the main Unayzah A reservoir. They are relatively continuous within a west-east trending depositional fairway that has been defined by both well and seismic data.
Early exploration targeting these reservoirs was centered on structural closures and resulted in the discovery of several large gas fields, like Tinat and Midrikah, the latter having a large stratigraphic trap component.
More recent exploration efforts have been focused in the areas northeast of those fields. A re-evaluation of legacy 3D seismic and interpretation of new 3D seismic and well data has led to an increased prospectivity within the Unayzah A reservoir interval. Methodologies applied there helped to refine the mapping of the hydrocarbon potential in the eolian fairway. Close re-examination of pre-existing and new seismic reflectivity and acoustic impedance 3D datasets through visualization, combined with spectral decomposition and rock properties modeling have given new insights into the distribution of the eolian reservoirs. High porosity sweet spots and the potential role of syntectonic structures in controlling sandstone deposition have been recognized.
Stratigraphic plays were identified in an area of about 8,000 sq km where no reliable structural closures are present. These plays are based on reservoir quality and the presence of lateral seals as inferred from seismic and well data.
Recent well results have given confidence not only in the ability to detect the porosity sweet spots, but also to discriminate which ones have higher probability of being filled with hydrocarbons, by combining rock properties analysis, modeling and pre-stack seismic data interpretation. The ongoing challenge is to further develop methodologies to discriminate between brine and hydrocarbon filled reservoirs to help prioritize the prospects already identified.