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Book Chapter

Reservoir Geology of the Middle Minagish Member (Minagish Oolite), Umm Gudair Field, Kuwait

By
Roger Davies
Roger Davies
Badley Ashton and Associates, Ltd., Winceby House, Winceby, Horncastle, Lincolnshire, LN9 6PB, U.K.
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;
Cathy Hollis
Cathy Hollis
Badley Ashton and Associates, Ltd., Winceby House, Winceby, Horncastle, Lincolnshire, LN9 6PB, U.K.
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;
Clive Bishop
Clive Bishop
BP Kuwait, P.O.Box: 29335, Safat, Kuwait.
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;
Ram Gaur
Ram Gaur
Kuwait Oil Company, P.O.Box: 9758, Ahmadi, Kuwait.
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;
Abdul Aziz Haider
Abdul Aziz Haider
Kuwait Oil Company, P.O.Box: 9758, Ahmadi, Kuwait.
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Published:
January 01, 2000

Abstract

The Minagish Oolite occurs in the Middle Minagish Member of the Minagish Formation (Berriasian-Valanginian) in Kuwait. Ten distinct lithofacies are recognized, which suggest sedimentation on a homoclinal carbonate ramp. A relatively small proportion of the Minagish Oolite (< 15%) consists of oolitic grainstone (Lithofacies 2), and this is confined to the lower part of the oil column. The dominant lithofacies comprises peloidal packstones to grainstones (Lithofacies 3). Sedimentation was highly storm-influenced, with significant reworking of shallow-water, inner-ramp skeletal allochems into the midrramp. The high level of reworking is believed to account for the relatively high proportion of grainstone and poorly washed packstones in the inner mid-ramp setting. The reservoir is interpreted as the product of sedimentation within late highstand, lowstand, and trasgressive systems tracts, which together represent a low- (third?) order relative sea-level change. Within each systems tract, laterally correlatable flooding surfaces at the tops of parasequences are directly overlain by thin units of bioturbated wackestones to packstones (Lithofacies 7). These wackestones to packstones are interpreted as deeper-water, outer-ramp environments, and indicative of higher-frequency, fourth- or fifth-order, cyclicity. There is strong evidence of a southwestward lateral facies change into more argillaceous limestones (“marls”) in the upper part of the Minagish Oolite. The geometry of the transition suggests that it marks the extreme fringe of a shallow-water clastic system. It represents the earliest evidence of delta progradation in the early Cretaceous of the Kuwait area. Evidence of associated shallowing is absent, and it seems that tectonic uplift in the hinterland was more influential than relative sea-level change.

Intense micritization has generated high proportions of microporosity, and it is the distribution of these micropores which mostly influences permeability. The best reservoir facies are grainstones of Lithofacies 2 and 3, where the pore network is macropore-dominated and microporosity is concentrated within micritized allochems. More heterogeneous packstones of Lithofacies 3 and 5 have mixed pore systems, whilst wackestones and packstones of Lithofacies 7 and 8 have micropore-dominated pore networks. In these samples, the pore network is dominated by interparticle micropores, and macroporosi try is rare and isolated. These microporous facies typically form laterally correlatable beds above flooding surfaces and are capable of forming baffles and barriers to vertical transmissibility. Overall, the proportion of facies exhibiting mixed and microporous pore systems increases upwards through the reservoir, and hence there is a corresponding decrease in reservoir quality. During the later stages of production, as the oil-water contact rises, increasingly detailed understanding of the reservoir architecture wil be required to maintain production levels. The lateral facies change at the top of the reservoir allied to increased compartmentalization indicates that a more comprehensive secondary recovery scheme will be required in this part of the reservoir.

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SEPM Special Publication

Middle East Models of Jurassic/Cretaceous Carbonate Systems

Abdulrahman S. Alsharhan
Abdulrahman S. Alsharhan
Faculty of Science United Arab Emirates University, P.O. Box 17551, Al Ain, U.A.E.
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;
Robert W. Scott
Robert W. Scott
Precision Stratigraphy Associates, RR3 Box 103-3, Cleveland, OK 74020, U.S.A.
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SEPM Society for Sedimentary Geology
Volume
69
ISBN electronic:
9781565761919
Publication date:
January 01, 2000

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