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7th Middle East Geosciences Conference and Exhibition
Manama, Bahrain
March 27-29, 2006
Reservoir
Characterization
and Stochastic Modeling of the 2nd Eocene Dolomite
Reservoir
,
Wafra Field, Divided Zone, Kuwait-Saudi Arabia
Divided Zone Group, Kuwait Gulf Oil Company, PTC Complex, KOC,
Ahmadi, Kuwait, 61008, Kuwait, phone: (+965) 6854920, fax: (+965) 3986598, [email protected]
The Wafra 2nd Eocene Reservoirs are dolomitized carbonates
associated with anhydrite deposited under shallow sub -tidal
to subkha environments. These are characterized by high porosity and permeability, mainly due to vugs formed by
enhancement of the predominantly intercrystalline porosity by leaching and dissolution. This vug dominated heteroloithic
pore system cuts across the depositional fabric that has largely been obliterated by dolomitization.
A relatively simple method of porosity modeling, using zonation based on high frequency cycles (HFCs) has been
attempted with good results. Based on core petrographic and electrolog studies, the reservoir
has been divided into 8
HFCs, further divisible into 14 ‘zones'. Porosity distribution is closely related to this HFC based zonation. Core porosities
show a decreasing upward trend between successive HFCs and the lower zone of each HFC has a higher porosity than the
upper. Mostly the vugs are localized to zones overlying the tighter, anhydrite rich crusts of the respective lower HFC.
The paper describes stochastic modeling of the reservoir
properties and their distribution in a high resolution 3D grid of
nearly 10 million cells covering an area of about 350km2 and average thickness of 500 feet. Vertically the grid was divided
into 14 stratigraphic layers based on the subdivision of the 8 HFCs. Porosity was distributed by sequential Gaussian
simulation, constrained by semivariogram models generated for each stratigraphic layer. Permeability was distributed by
applying powerlog porosity – permeability transforms developed for each stratigraphic layer from core data. Water
saturation distribution was further constrained by the model porosity distribution and the oil water transition zone.