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Formation of detrital clay grain coats by dewatering of deep-water sands and significance for reservoir quality

Kristin W. Porten, Michal J. Warchol and Ian A. Kane
Formation of detrital clay grain coats by dewatering of deep-water sands and significance for reservoir quality
Journal of Sedimentary Research (December 2019) 89 (12): 1231-1249

Abstract

Well-developed detrital clay grain coats are observed in deep-marine sandstones of the Upper Cretaceous Springar Formation of the Voring Basin in the Norwegian Sea. The detrital clay coats form thin and compact rims on individual sand grains and meniscus-shaped bridges between grains. These well-developed coats are found in high-density turbidites and proximal hybrid event beds with common to pervasive dewatering structures deposited in proximity to the base of a syndepositionally active basin high. Here, in one exploration well, detrital clay grain coats are common throughout a sandstone package 100 m thick. High-density turbidites and proximal and distal hybrid event beds drilled in mid- to distal-fan settings unaffected by seismically resolved seafloor topography show common dewatering features, but have only scattered detrital clay coats confined to individual dewatering pipes or dish structures. Hence, we propose that intense sediment dewatering has the potential to form detrital clay coats in deep-marine sandstones by a combination of elutriation and reorganization of clays during fluid escape from sediment bodies with pore fluid pressures significantly higher than the hydrostatic pressure. In submarine fan systems, deposition of sediment with coeval trapping of large volumes of interstitial pore fluid is most likely to occur where gravity flows undergo rapid deceleration in response to an abrupt decrease in confinement or gradient. Such environments include the channel-lobe transition and settings in proximity to seabed topography. The investigated sandstones are quartz arenites and subarkoses, with minor to moderate volumes of quartz cement (up to 6%). However, strongly to completely quartz-cemented intergranular pore space is observed where detrital clay coats or matrix does not cover quartz grains in the deepest part of the studied formation. Modeling of quartz cementation predicts that most intergranular macroporosity in the lower part of the Springar Formation would be quartz cemented if the sandstones were free of detrital clays. Based on our observations and modeling results we propose that intense sediment dewatering has the potential to form detrital clay coats, which can be important for retaining porosity in deeply buried sandstones and in basins with high present or past heat flow.


ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 89
Serial Issue: 12
Title: Formation of detrital clay grain coats by dewatering of deep-water sands and significance for reservoir quality
Affiliation: Equinor ASA, Bergen, Norway
Pages: 1231-1249
Published: 201912
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 98
Accession Number: 2020-006904
Categories: Sedimentary petrologyEconomic geology, geology of energy sources
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 3 tables, geol. sketch map
N64°00'00" - N67°49'60", E03°00'00" - E10°00'00"
Secondary Affiliation: University of Manchester, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, 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: 202006
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