The effects of clay diagenesis on petrophysical properties of the lower Cretaceous sandstone reservoirs, Orange Basin, South Africa

Abstract

Research Article| March 01, 2016 The effects of clay diagenesis on petrophysical properties of the lower Cretaceous sandstone reservoirs, Orange Basin, South Africa C. Samakinde; C. Samakinde Department of Earth Sciences, University of the Western Cape, Robert Sobukwe Road, Bellville, Cape Town, South Africa e-mail: chrissamakinde@gmail.com Search for other works by this author on: GSW Google Scholar M. Opuwari; M. Opuwari Department of Earth Sciences, University of the Western Cape, Robert Sobukwe Road, Bellville, Cape Town, South Africa e-mail: mopuwari@uwc.ac.za Search for other works by this author on: GSW Google Scholar J.M. van Bever Donker J.M. van Bever Donker Department of Earth Sciences, University of the Western Cape, Robert Sobukwe Road, Bellville, Cape Town, South Africa e-mail: jvanbeverdonker@uwc.ac.za Search for other works by this author on: GSW Google Scholar Author and Article Information C. Samakinde Department of Earth Sciences, University of the Western Cape, Robert Sobukwe Road, Bellville, Cape Town, South Africa M. Opuwari Department of Earth Sciences, University of the Western Cape, Robert Sobukwe Road, Bellville, Cape Town, South Africa J.M. van Bever Donker Department of Earth Sciences, University of the Western Cape, Robert Sobukwe Road, Bellville, Cape Town, South Africa e-mail: chrissamakinde@gmail.com e-mail: mopuwari@uwc.ac.za e-mail: jvanbeverdonker@uwc.ac.za Publisher: Geological Society of South Africa First Online: 20 Nov 2017 Online Issn: 1996-8590 Print Issn: 1012-0750 © 2016 March Geological Society of South AfricaGeological Society of South Africa South African Journal of Geology (2016) 119 (1): 187–202. https://doi.org/10.2113/gssajg.119.1.187 Article history First Online: 20 Nov 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation C. Samakinde, M. Opuwari, J.M. van Bever Donker; The effects of clay diagenesis on petrophysical properties of the lower Cretaceous sandstone reservoirs, Orange Basin, South Africa. South African Journal of Geology 2016;; 119 (1): 187–202. doi: https://doi.org/10.2113/gssajg.119.1.187 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract Authigenesis of clay minerals occurs during rock-fluid interactions in the subsurface, and inevitably occludes the pore spaces of clastic reservoirs. The presence of authigenic clay minerals defines the pore geometry of clastic reservoirs, which could impact on drilling and production of hydrocarbons by affecting subsurface pressure, and reducing hydrocarbon recovery, respectively. The latter has made clay diagenesis study a major component of reservoir quality assessment studies, and consequently an important area of research. Here we explore how clay diagenesis affects the basic petrophysical properties (porosity, permeability and saturation) of lower Cretaceous sandstone reservoirs of two wells (AU-1 and KH-1) along the west coast of South Africa. We use petrographical (SEM and thin-section analysis), geochemical (Pore water chemistry, XRD and CEC), and geophysical (wireline logs interpretation) tools in our study. Clay minerals present include kaolinite, illite, and montmorillonite. Illite occurs as the grain coating mineral, and kaolinite as pore filling mineral. Average porosity values of 8.5% (9.6%), effective porosity of 3.3% (9.5%), permeability range of 0.001 to 0.03 mD (0.005 to 0.2mD), and average water saturation of 51% (27%) from wells AU1 and KH1, respectively, were obtained. The low resistivity, poor porosity and permeability values recorded are attributed to the presence of the dominant clay minerals (illite, kaolinite and montmorillonite) within the reservoir intervals. Generally, the dominant cement in the sediment is quartz with calcite and pyrite in traces. The presence of calcite and glauconite in the reservoir rocks is an indication that the sediments were deposited in shallow marine conditions. It is concluded that all these minerals likely contributed to the low values encountered for porosity and permeability, as well as the moderate water saturation levels in the reservoir intervals. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.