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Experimental study of chlorite authigenesis and influence on porosity maintenance in sandstones

Dimitrios Charlaftis, Stuart J. Jones, Katherine J. Dobson, Jonathan Crouch and Sanem Acikalin
Experimental study of chlorite authigenesis and influence on porosity maintenance in sandstones
Journal of Sedimentary Research (February 2021) 91 (2): 197-212

Abstract

Chlorite is recognized as a key mineral for preserving reservoir quality in deeply buried sandstones, as chlorite coatings inhibit the nucleation of quartz overgrowths. A limited understanding of the mechanisms and conditions under which these authigenic chlorite coatings form prevents the accurate forward modeling of diagenesis and limits reservoir quality models critical to a wide range of geoscience applications. We present experimental data that show how authigenic chlorite grain coatings preserve porosity in deeply buried sandstone reservoirs, using a series of hydrothermal reactor experiments to simulate quartz cementation and capture the evolving porosity. To simulate reservoir evolution, berthierine-bearing sandstone samples (Lower Jurassic Cook Formation, Oseberg Field, 30/6-17R, Norway) were exposed to a silica-supersaturated Na (sub 2) CO (sub 3) (0.1 M) solution for 72 hours at temperatures of between 100 and 250 degrees C. Quantification of the temperature-dependent changes in the volume of authigenic chlorite, the thickness and coverage of the clay coatings, and the sample porosity shows increases in chlorite volume (from approximately 2% to approximately 14%). This occurs by the transformation, of patchy amorphous berthierine into grain-coating Fe-chlorite cements through a mixture of the solid-state transformation and dissolution-precipitation mechanisms, siderite replacement, and direct precipitation on clay-free surfaces. With increasing temperature, the chlorite coatings increase from approximately 3.8 mu m to approximately 5.4 mu m thick and expand their grain surface coverage from approximately 28% to approximately 50%. The face-to-edge and face-to-face foliaceous structure of the clay coatings produced are morphologically similar to those observed in deeply buried sandstones. Only above temperatures of 175 degrees C is porosity preserved as a consequence of inhibition of quartz overgrowths and the generation of secondary porosity. Our quantitative approach enhances our knowledge regarding the temperature and mineral precursor influence on chlorite-coating authigenesis and therefore provides key insight for chlorite grain coatings for reservoir potential in sedimentary sequences greater than 2.5 km.


ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 91
Serial Issue: 2
Title: Experimental study of chlorite authigenesis and influence on porosity maintenance in sandstones
Affiliation: Durham University, Department of Earth Sciences, Durham, United Kingdom
Pages: 197-212
Published: 202102
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 74
Accession Number: 2021-027790
Categories: Sedimentary petrologyEconomic geology, geology of energy sources
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
N60°27'00" - N60°42'00", E02°37'60" - E02°52'00"
Secondary Affiliation: University of Strathclyde, Department of Civil & Environmental Engineering, GBR, United KingdomBP, GBR, United KingdomNewcastle University, School of Natural and Environmental Sciences, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 2021
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