TY - JOUR
T1 - Stratigraphically controlled silicification in Danian chalk and its implications for reservoir properties, southern Danish Central Graben
AU - Blinkenberg, Kasper H.
AU - Anderskouv, Kresten
AU - Sheldon, Emma
AU - Bjerrum, Christian J.
AU - Stemmerik, L.
N1 - Funding Information:
The authors kindly acknowledge the Danish Underground Consortium (Total, Noreco and Nordsøfonden) for permission to publish this study. We extend warm appreciation to Thomas Blume (Total) and the staff at the Total Core Laboratory in Copenhagen for allowing access to plugs and core material in addition to accessibility to the photo equipment. Jon Ineson and Bodil W. Lauridsen (both GEUS) are thanked for their assistance with macroscopic characterisation and trace fossil identification. Peter Frykman (GEUS) is acknowledged for providing an overview of accessible core and plug data, and Emma Haxen (previously University of Copenhagen) is thanked for constructive dialogue concerning the use and limits of HH-XRF analysis. The authors thank three anonymous reviewers for the constructive feedback that improved the manuscript. This project was financially supported by the Danish Hydrocarbon Research and Technology Centre ( DHRTC ).
Funding Information:
The authors kindly acknowledge the Danish Underground Consortium (Total, Noreco and Nords?fonden) for permission to publish this study. We extend warm appreciation to Thomas Blume (Total) and the staff at the Total Core Laboratory in Copenhagen for allowing access to plugs and core material in addition to accessibility to the photo equipment. Jon Ineson and Bodil W. Lauridsen (both GEUS) are thanked for their assistance with macroscopic characterisation and trace fossil identification. Peter Frykman (GEUS) is acknowledged for providing an overview of accessible core and plug data, and Emma Haxen (previously University of Copenhagen) is thanked for constructive dialogue concerning the use and limits of HH-XRF analysis. The authors thank three anonymous reviewers for the constructive feedback that improved the manuscript. This project was financially supported by the Danish Hydrocarbon Research and Technology Centre (DHRTC).
Publisher Copyright:
© 2019 Elsevier Ltd
PY - 2020/5
Y1 - 2020/5
N2 - The effect of silica on reservoir quality in chalk is subject to continuing debate. In particular, the stratigraphic variations in silica content within the chalk matrix have not been addressed sufficiently. In this study, a new approach is applied to constrain silica variability in reservoir chalk utilizing hand-held X-ray fluorescence (HH-XRF) on samples from four Maastrichtian–Danian cores from hydrocarbon-producing fields in the southern Danish Central Graben. The results indicate a significant lateral and stratigraphic variability in silica concentrations across the study area; data display a common stratigraphic signature in all wells, however, with maximum silica concentrations and minimum porosities occurring in the lower part of the Danian Ekofisk Formation. Correlation between HH-XRF quantified silica concentrations and biostratigraphic data indicates the synchronous onset of an at least semi-regional silica event during the mid-Danian, nannofossil zones NNTp2F–G to NNTp4A–D, whereas the upper boundary of the peak silica unit is poorly constrained. Generally, stratigraphic trends in silica concentrations appear to be negatively correlated with porosity trends. However, comparison between the HH-XRF quantified silica content and reservoir data (porosity, permeability, estimated pore radius and calculated specific surface area) shows poor correlation indicating that silica content within the Ekofisk reservoir is not the only factor controlling the reservoir quality. Unknown complex diagenetic interactions between calcite, silica and clay probably influence the reservoir properties by promoting calcite cementation in stratigraphically controlled zones, making the Ekofisk reservoir much less predictable than the underlying Maastrichtian Tor Formation.
AB - The effect of silica on reservoir quality in chalk is subject to continuing debate. In particular, the stratigraphic variations in silica content within the chalk matrix have not been addressed sufficiently. In this study, a new approach is applied to constrain silica variability in reservoir chalk utilizing hand-held X-ray fluorescence (HH-XRF) on samples from four Maastrichtian–Danian cores from hydrocarbon-producing fields in the southern Danish Central Graben. The results indicate a significant lateral and stratigraphic variability in silica concentrations across the study area; data display a common stratigraphic signature in all wells, however, with maximum silica concentrations and minimum porosities occurring in the lower part of the Danian Ekofisk Formation. Correlation between HH-XRF quantified silica concentrations and biostratigraphic data indicates the synchronous onset of an at least semi-regional silica event during the mid-Danian, nannofossil zones NNTp2F–G to NNTp4A–D, whereas the upper boundary of the peak silica unit is poorly constrained. Generally, stratigraphic trends in silica concentrations appear to be negatively correlated with porosity trends. However, comparison between the HH-XRF quantified silica content and reservoir data (porosity, permeability, estimated pore radius and calculated specific surface area) shows poor correlation indicating that silica content within the Ekofisk reservoir is not the only factor controlling the reservoir quality. Unknown complex diagenetic interactions between calcite, silica and clay probably influence the reservoir properties by promoting calcite cementation in stratigraphically controlled zones, making the Ekofisk reservoir much less predictable than the underlying Maastrichtian Tor Formation.
KW - Calcareous nannofossil biostratigraphy
KW - Chalk Group
KW - Ekofisk Formation
KW - Handheld X-ray fluorescence (HH-XRF)
KW - Reservoir characterisation
KW - Silica distribution
UR - http://www.scopus.com/inward/record.url?scp=85078996157&partnerID=8YFLogxK
U2 - 10.1016/j.marpetgeo.2019.104134
DO - 10.1016/j.marpetgeo.2019.104134
M3 - Article
AN - SCOPUS:85078996157
VL - 115
JO - Marine and Petroleum Geology
JF - Marine and Petroleum Geology
SN - 0264-8172
M1 - 104134
ER -