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Geological Society, London, Special Publications; 1990; v. 50; p. 299-316;
DOI: 10.1144/GSL.SP.1990.050.01.16
© 1990 Geological Society of London

Geology and reservoir characteristics of Lower Cretaceous Kharaib Formation in Zakum Field, Abu Dhabi, United Arab Emirates

A. S. Alsharhan

Geology Department, United Arab Emirates University, P.O. Box: 15551, Al Ain, United Arab Emirates

The Zakum oil field is an east-west plunging anticline, located in offshore Abu Dhabi, UAE. The field was discovered in 1963 by seismic survey, and came on production in 1967 at an initial rate of 50 000 bopd from the Lower Cretaceous carbonate sediments. The Zakum structure is a broad asymmetric anticlinal feature characterized by gentle dips throughout; the steepest dips occur in the north and northeast where the average dip is about 2.5°. The structure is about 45 km long and 28 km wide, and has a vertical closure in excess of 1200 ft.

At Zakum field the Lower Cretaceous Thamama Group is a thick shallow-marine carbonate sequence with an average thickness of about 2300 ft, and is divided into four formations: Shuaiba, Kharaib, Lekhwair and Habshan (in descending order). An informal reservoir-oriented classification was set up for this group. It was subdivided into six zones given a numerical notation from top to bottom (Zones I to VI).

The Kharaib Formation represent shallowing upward cycles formed in very shallow epicontinental seas. The energy level grades from low-energy subtidal to high-energy setting at or above wave base. It is characterized by dense-argillaceous pyritic bioclastic lime mudstones/wackestones, peloidal-ooidal packstones/grainstones, dolomitic limestones and thin black shale laminae.

The reservoir quality of the formation is controlled by vertical and lateral distribution of porosity, permeability and stylolites. The porosities ranges from 5 to 28%, and permeabilities from less than 1 to 100 Md. The influence of initial environment of deposition, diagenesis and petrophysical properties on the reservoir characteristics is evaluated.





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[Abstract] [Full Text] [PDF]