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Reservoir Characterization, with Emphasis from Ghazal Formation, Upper Cretaceous, Unity Field, Muglad Basin, SW Sudan

Musab M. Elmahi1 and Omer Elbadri Ali2
1Development, GNPOC, Khartoum, Sudan
2Department of Geology, University of Khartoum, Khartoum, Sudan

The Campanian- Maastrichian continental fluvial Ghazal Formation has been investigated based on data obtained from ten (10) wells in the Unity field, Muglad Basin. Various methods have been used in the present study including different sedimentological, petrographical and petrophysical techniques as well as conventional cores, polarized microscope, X-ray diffraction analysis, Scanning electron microscopy, mudlogs and wireline logs.

The lithofacies analysis allowed the sub-division of Ghazal Formation into lower and upper parts. The lower Ghazal Formation is composed of coarse lithofacies of sandstone that reveal fining upwards sequences of braided stream channels. The upper Ghazal Formation is dominated by fine sandstone, siltstone and claystone that reveal coarsening upward sequence of meandering rivers.

The stratigraphic successions of lithological facies and depositional patterns of Ghazal Formation reflect mainly allocyclic and autocyclic controls such as tectonic activity, climate, drainage system, and sediment load. The stratigraphic thickness of the formation was measured from logs and found to be ranging from 213m - 182m.
The clay mineral of Ghazal Formation mainly consists of kaolnite, smectite, illite and chlorite. The kaolinte and semcitite indicate a warm humid climate interrupted by dry seasons. The clay mineral assemblages of Ghazal Formation show relationship with lithfacies types and depositional system.

The diagenetic event has played considerable role in modifying the original framework components as well as the primary intergranular porosity of these sandstones. The present-day porosity average is about 22 - 24. Permeability ranges average is about 103 - 596 md.

The reservoir is relatively thicker in the units Ghazal-D and Ghazal-H, and the shape of sand bodies are mainly sheet and massive in these layers, and have good lateral continuity.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery