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

Charlaftis, D; Jones, S.J; Dobson, K.J; Crouch, J; Acikalin, S

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


Authors

K.J Dobson

J Crouch

S Acikalin



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 Na2CO3 (0.1 M) solution for 72 hours at temperatures of between 100 and 250 °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 ∼ 2% to ∼ 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 ∼ 3.8 μm to ∼ 5.4 μm thick and expand their grain surface coverage from ∼ 28% to ∼ 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 °C is porosity preserved as a consequence of inhibition of quartz overgrowths and the generation of secondary porosity.

Journal Article Type Article
Acceptance Date Dec 21, 2020
Online Publication Date Mar 25, 2021
Publication Date 2021
Deposit Date Feb 4, 2021
Publicly Available Date Nov 15, 2021
Journal Journal of Sedimentary Research
Print ISSN 1527-1404
Publisher Society for Sedimentary Geology (SEPM)
Peer Reviewed Peer Reviewed
Volume 91
Issue 2
Pages 197-212
DOI https://doi.org/10.2110/jsr.2020.122
Public URL https://durham-repository.worktribe.com/output/1247007

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Accepted Journal Article (3.4 Mb)
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Copyright Statement
Accepted for publication in Journal of Sedimentary Research as of 21 December 2020.






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