South Africa - Inkaba.org

Facies architecture and reservoir quality of Fan B, Permian
Laingsburg Formation, southwestern Karoo Basin, South
Africa
D. Lombard 1 , D. Mikeš 2 , P. Carey 3
1. Department of Geology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa,
15956717@sun.ac.za
2. Department of Geology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa, South
Africa, mikes@sun.ac.za
3. University of Western Cape, Private Bag X17, Bellville 7535, South Africa, pcarey@uwc.ac.za
ABSTRACT
In recent years hydrocarbon exploration companies have shifted their attention to slope areas and associated
depositional environments. Slope fans develop at the base-of-slope and downlap onto the basin floor. Slope fans
are characterized by channel-levee complexes and are predicted to be dominated by mud-rich systems. The proven
and prolific Gulf of Mexico, offshore Angola, Nile and Niger delta slope reservoirs stands testament to the great
potential contained within slope hydrocarbon reservoirs.
Presently while the Karoo Basin is strongly compacted, it can nevertheless be used as an outcrop reservoir analog.
Facies outcrop characterization studies provides a means to obtain vertical and lateral attributes of strata and their
bounding surfaces, help reduce uncertainty in lithology prediction, and bridge the gap between wireline logs and
seismic scales of resolution.
The main aim of this study is to provide a clear understanding and description on reservoir heterogeneity in terms
of facies, porosity and permeability variations, within Fan B (base-of-slope) of the Laingsburg Formation based on
petrographic data. The objectives of the study are to 1) determine lateral continuity and vertical connectivity of
sedimentary units, 2) mitigate the effect of baffles and barriers to oppose flow capabilities, 3) describe textural and
compositional characteristics 4) establish the distribution of diagenetic alterations and their impact on reservoir
quality.
A sedimentological and stratigraphical study will be undertaken, which will include the description of facies and
depositional elements within the upper, middle and lower parts of Fan B. Descriptions will include lithotype,
sedimentary structures, bouma divisions, bounding surfaces and connectivity, thicknesses, net-to-gross ratios, grain
size, geometry, process of deposition and interpretation, identification of baffles and barriers to oppose flow,
construction of sedimentary logs, and hand sampling from surface outcrops. The various samples taken at the
different locations will be subjected to XRD, thin-sectioning, and SEM analyses. The XRD will be used to
quantitatively identify minerals in rock samples. XRD provides reliable mineralogical abundance data and allows
for accurate calculations to be made from mineralogical constituents that make up the rock. Thin sections will be
used to determine mineralogical and textural features, including porosity and connectivity of pore spaces.
Descriptions will include the degree of sorting, mean grain size of samples, grain shape, mineral constituents,
mineral alterations, dominant cements, and compaction effects. SEM will be used to provide valuable insight on
the structure of major diagenetic products effecting pore spaces and pore throats at pore/ grain scale.
The expected outcomes/- deliverables of the study include 1) sedimentological and stratigraphical model 2)
reservoir characteristic and comparison of lower, middle and upper fan facies, 3) development of 2D or 3D model
from outcrop profiles, 4) unravelling the main controls on mud-rich fans and 5) reservoir implications of outcrop
and petrographical characteristics, and possible application to other similar depositional settings.
KEYWORDS: Karoo Basin, slope turbidite channels, reservoir quality, diagenesis
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