Petrography, Sedimentology and Reservoir Geology of Aradeiba and Bentiu Formations, Block 5A (Tharjath Oil Field) South Sudan
Petrography, Sedimentology and Reservoir Geology of Aradeiba and Bentiu Formations, Block 5A (Tharjath Oil Field) South Sudan
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Authors
Sherif, Mohamed Abdalla Murad
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Publisher
University of Khartoum
Abstract
A research on five wells data was achieved with the objectives of
carrying out a detailed and comprehensive study to investigate and
describe textures, mineralogy, digenesis, facies, porosity and
permeability characteristics and controls on the Bentui and Aradeiba
reservoirs. The aim was also to essentially construct a conceptual
depositional model summarizing the probable geometries and
relationships of the major sand-body types and properties in order to
fully understand and asses the reservoir sands characteristics, controls
and distribution.
Methods of petrographic analysis, XRD, and SEM on cores and ditch
samples aided by Petrophysical wire line logs and Cyclolog® technique
were used for determination of facies, porosity, permeability, sand to
shale ratios, correlations and spatial sands distribution.
Interpretation and integration of the study results revealed that the
Aradeiba Formation consist mainly of interbedded sequences of shale and
sandstone but mostly argillaceous. In the lower part, the interbeded
sands thicknesses range from 2.5 to 18 m having good reservoir
properties with porosity range from 7.9% to 24.9 % and variable
permeability from 0.08 mD to 5.3D. The identified lithofacies and cycles
patterns indicate that Aradeiba has been deposited within a high
sinuosity/meandering fluvial channel and locally prograding deltaic
deposits system, with less sands lateral continuity. The upper part is
considered essentially as non- reservoir due to abundant mud materials
and acts as top/lateral seal within Tharjath field.
The underlying Bentiu reservoir sandstones represents thick stacked
poorly consolidated sands with 2.3 to 21 m in thickness having porosity
ranges from 12.9% to 31.6% and permeability varying between 0.54 mD
to 7.9D. The deposional cycles and facies recognized indicate the
dominance of low sinuosity/braided fluvial channel environment
characterized by good reservoir sands quality and lateral continuity.
This reservoir characterization is very essential for future planning of
wells drilling, optimum well completion, field development and reserves
calculation economics.
Description
Keywords
Petrography, Sedimentology,
Reservoir Geology,
Aradeiba,
Bentiu Formations,
Block 5A (Tharjath Oil Field),
South Sudan