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Diagenesis and porosity development in the first Eocene reservoir at the giant Wafra Field, partitioned zone, Saudi Arabia and Kuwait

Arthur H. Saller, David Pollitt and J. A. D. Dickson
Diagenesis and porosity development in the first Eocene reservoir at the giant Wafra Field, partitioned zone, Saudi Arabia and Kuwait
AAPG Bulletin (June 2014) 98 (6): 1185-1212

Abstract

The First Eocene reservoir at the Wafra Field produces heavy oil from very porous dolomites at depths of approximately 1000 to 1300 (300 to 400 m) in the Paleocene-Eocene Umm Er Radhuma Formation. Porosity is commonly 30-50%, permeability is commonly 100-2000 md, and those reservoir characteristics were determined largely by diagenesis. Early diagenesis is dominated by dolomitization, dissolution associated with dolomitization, and precipitation of sulfates. Petrographic and stable isotopic characteristics support dolomitization and sulfate precipitation in evaporated (refluxing) seawater during shallow burial. The highest permeabilities occur in subtidal facies. Low-permeability tidal-flat facies stratify the reservoir. Heavy oil preferentially filled high-permeability dolomites; whereas, low-permeability tidal-flat facies are commonly filled with water because their pore throats are too small to allow migration of viscous oil into the rock. This reservoir"s very high porosity is probably related to its shallow burial and early oil emplacement. Late-stage diagenesis is dominated by bacterial sulfate reduction (BSR) that caused dissolution of sulfate nodules, calcite cementation, sulfur precipitation, and oil biodegradation. The BSR is indicated by very low delta (super 13) C compositions of calcite cements (-17.1 to -34.9 ppm, Peedee Belemnite standard), which require an organic carbon source; probably oil. The oxygen isotopic compositions of the calcites support precipitation from formation waters similar to those in the reservoir now. The BSR probably started during initial oil emplacement and continues to the present. The BSR was heterogeneous resulting in produced oils with gravities of 14-21 degrees API. Even heavier oils are present that could not flow during primary production. Primary production was likely greatest in areas and intervals with lighter, less viscous oil.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 98
Serial Issue: 6
Title: Diagenesis and porosity development in the first Eocene reservoir at the giant Wafra Field, partitioned zone, Saudi Arabia and Kuwait
Affiliation: Cobalt International Energy, Houston, TX, United States
Pages: 1185-1212
Published: 201406
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
References: 48
Accession Number: 2014-048973
Categories: Economic geology, geology of energy sourcesSedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., strat. col., 3 tables, sketch maps
N28°30'00" - N30°15'00", E46°30'00" - E48°45'00"
N17°00'00" - N32°30'00", E34°45'00" - E57°00'00"
Secondary Affiliation: Chevron Corporation, USA, United StatesUniversity of Cambridge, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States
Update Code: 201427
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