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OIL‐IMPREGNATED FLINT IN DANIAN CHALK IN THE TYRA FIELD, NORTH SEA CENTRAL GRABEN
Author(s) -
Jakobsen F.,
Lindgreen H.,
Nytoft H.P.
Publication year - 2014
Publication title -
journal of petroleum geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.725
H-Index - 42
eISSN - 1747-5457
pISSN - 0141-6421
DOI - 10.1111/jpg.12568
Subject(s) - geology , porosity , nodule (geology) , quartz , porosimetry , sedimentary depositional environment , mineralogy , geochemistry , paleontology , structural basin , porous medium , geotechnical engineering
A new model has recently been proposed for the formation of flint in Danian North Sea chalk, according to which nano‐quartz spheres crystallized in the marine water column and were then deposited and compacted, ultimately forming flint. This depositional origin implies that apparently massive flint blocks may have a porous structure. Internal flint porosity is supported by observations on an oil‐impregnated flint nodule recovered from the gas and oil zone in the Tyra field, well E‐5. Samples from the flint nodule have been investigated – the mineralogy by X‐ray diffraction and thermal analysis, and the structure by Atomic Force Microscopy (AFM) and helium porosimetry. In addition, organic‐geochemical analyses of the hydrocarbons in the flint nodule were carried out. The structure of the flint, which is composed of nano‐size spheres, indicates that significant porosity related to micro‐sized pore spaces may be present. Measurements on the flint nodule using standard He‐porosimetry demonstrate a porosity of 16.5% which is of the same order of magnitude as that measured in the overlying chalk. The oil extracted from the nodule has a composition similar to that present in other reservoirs nearby. The presence of oil in the flint nodule examined suggests that the porous proto‐flint formed part of the reservoir section as both chalk and flint were filled simultaneously with hydrocarbons.