Integration of routine core data and petrographic analysis to determine the sandstone reservoir flow units in the Bredasdorp Basin, Offshore South Africa
Loading...
Date
2024-11
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Fort Hare
Abstract
The integration of routine core data and petrography to determine the sandstone reservoir flow units was extensively performed in four selected wells: F-A10, F-A13, FO1, and F-O2 in the Bredasdorp Basin, offshore South Africa. Determining the quality of reservoirs and identifying minerals present is crucial for defining the best reservoir interval for hydrocarbon flow and storage and avoiding exploration errors by using suitable drilling and hydraulic fluids. Moreover, it also helps select the best Enhanced Oil Recovery (EOR) methods. The analysed wells were randomly chosen throughout the upper shallow marine interval to examine the impact of diagenetic minerals on reservoir flow units using geophysical wireline logs, routine core analysis, and core samples. The routine core analysis data consisted of nine hundred core plugs, which were used to establish reservoir flow units from four independent methods, namely: Pore Throat Radius, Flow Zone Indicator, Stratigraphic Modified Lorenz Plot, and Improved Stratigraphic Modified Lorenz Plot. The analysis of seventeen thin sections and fifteen scanning electron microscopy samples were employed to determine the impact of diagenetic minerals on petrophysical properties. The gamma-ray log and core samples identified one reservoir from each well. The permeability and porosity of the four identified sandstone reservoirs ranged from 0–22% and 0–2250 mD, respectively. The Stratigraphic Modified Lorenz Plot results showed five flow units classified as high, moderate, low, very low, and tight reservoir rock. In contrast, the Improved Stratigraphic Modified Lorenz Plot showed six flow units: fractured, super-conductive, conductor, semi-conductor, baffle, and semi-barrier. The Improved Stratigraphic Modified Lorenz Plot method proved more effective than the Stratigraphic Modified Lorenz Plot method in identifying flow units. The pore throat radius revealed that the pores ranged from nano-porous (≤ 1 𝜇𝑚) to megaporous (≥ 10 𝜇𝑚). The best reservoir intervals had megaporous radii and were classified as high or super-conductive flow units. In contrast, the poorer or impervious reservoir intervals had nanoporous radii and were classified as tight or baffle flow units. Four hydraulic flow units were identified and ranked as impervious, poor, fair, and good. Core logging of selected reservoirs revealed that FA10 and F-A13 were composed of glauconitic, medium-grained sandstone, fine-grained sandstone, and claystone. F-O1 was composed of fine-to-coarse grained sandstone that was moderately to well-sorted. F-O2 comprised of fine-grained, argillaceous sandstones that were poorly to moderately sorted. The Scanning Electron Microscopy analysis revealed that the clay minerals in the selected wells were smectite, illite, and chlorite. The effect of diagenetic minerals on petrophysical properties was apparent in the pore-filling minerals (glauconite, siderite, smectite, illite, chlorite, quartz and feldspar overgrowth, calcite, and calcareous sponge), which affected intergranular pore spaces and pore connectivity. Various diagenetic processes, such as cementation, compaction, and pore-filling minerals, significantly impacted the reservoir petrophysical characteristics of the studied reservoirs, particularly the F-O2 reservoir. These results can serve as input parameters for the Bredasdorp Basin's static and dynamic reservoir models.
Description
Master of Science in Geology
Keywords
Porosity, Permeability, Sandstone, Petroleum -- Geology
Citation
yhutyhani, N. (2024) Integration of routine core data and petrography analysis to determine the sandstone reservoir flow units in the Bredasdorp Basin, offshore South Africa. MSc (Geology) dissertation. Alice, South Africa: University of Fort Hare