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Reservoir Sweet Spots in the Arabian Petroleum Basin; Types and Controls

Khalil, Mesbah H.*1
(1) Saudi Aramco, Dhahran, Saudi Arabia.

Reservoir sweet spots are areas with better permeability relative to their surroundings. They represent a major challenge in exploration and development. This abstract describes the types of reservoir sweet spots in the Arabian basin and the most common factors controlling their development. Three types of reservoir sweet spots are identified in the Arabian basin; tectonic, sedimentologic and diagenetic. The tectonic sweet spots are areas with open fractures being the main control of reservoir productivity. The sedimentologic sweet spots are areas with coarser-grained than the surrounding clastics, or areas where porous carbonate build-ups exist. The diagenetic sweet spots are areas with better permeability due to re-crystallization, dissolution, or dolomitization. The reservoir sweet spots result from one or more of three factors; a) local redistribution of tectonic stresses, b) combined effects of sea level changes and sediment accumulation, and c) diagenetic processes. The effect of redistributing stress at local fabric acts directly and indirectly on developing sweet spots. Direct effects result in open fractures in the higher stress concentration zones. Indirect effects take place in structural settings that are favorable for the sedimentologic and diagenetic sweet spots. Structural ramps and fault drag zones are favorable structural settings for sedimentologic sweet spots in clastic and carbonate reservoirs. Open fractures and releasing fault bends are favorable structural settings for diagenetic sweet spots. Areas with higher subsidence rate along clastic fairways, and clastic entry points (structural ramps) developed sedimentologic clastic sweet spots within the Paleozoic and mid-Cretaceous in the Arabian basin. Carbonate reservoir sweet spots in the Arabia basin are believed of high potential due to the basin being made-up of several mini sub-basins. The edges of the sub-basins act as favorable areas for developing carbonate sweet spots (shallow water). Diagenetic processes were more active in developing diagenetic sweet spots in areas with faster fluid flow along faults and open fractures. In these areas, dolomitization of tight limestones improve the reservoir permeability. Re-crystallization due to fluid flow increases the rock brittleness that increases its susceptibility for fracturing by tectonic stresses, this generates combined diagenetic fractured reservoir sweet spots.

 

AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain