1887

Abstract

Summary

A study of the geochemistry and petrology characterizing the North Sea reservoir chalk is central in the efforts of refining or developing new Increased Oil Recovery (IOR) methods, as it provides an insight in the chemical composition, mineral structures and textures of the reservoir rock and the grounds for a pilot test within the National IOR Centre of Norway. The study is based on cores collected over a decimeter-scale, under different flooding status, from unflooded to waterflooded at lower or higher temperatures, swept and unswept regions from the Tor and Ekofisk formations directly sampled from the Ekofisk field. Optical petrography shows a very fine, micritic carbonate matrix, with various microfossils such as calcispheres, foraminifers, or sponge spicules. SEM micrographs reveal post-depositional calcite precipitation inside the calcispheres, sometimes entirely cementing their cavities. The amount of clay minerals observed with SEM varies and there is a clear decrease in porosity stratigraphically downwards, along with more cementation and compaction. X-ray diffraction confirms calcite as most abundant in the whole-rock composition, with quartz and few other non-carbonate minerals like smectite, illite and kaolinite present. The silica content varies highly from <2 wt% in the shallower cores to 6 – 8 wt% in areas close to tight zones and up to 11 wt% in the deeper cores. δ13C and δ18O are lower than the secular global isotopic values for this period. Since similar disturbed stable isotope values are seen in other hydrocarbon-rich samples unexposed to any fluid for IOR purposes, the disturbance is assigned to a post-depositional diagenetic overprint, or to the influence of a secondary fluid of unknown origin, rather than the effect of the cores’ flooding status.

Given the compositional variety of the Ekofisk reservoir rocks, selecting a single on-shore exposure as a standard equivalent for the Ekofisk chalk would be problematic. The complexity of the reservoir chalk and consideration of many other IOR influencing parameters, compel caution when transferring results from the onshore chalk modeling to the reservoir chalk (e.g. ). Beside the mineralogical composition of chalk strongly influencing compaction, the palaeo-environmental conditions at the time of deposition, the diagenetic history, calcite recrystallization and fossil preservation may affect the strength of the rock. Hence, a further thorough geological study on the reservoir chalk is necessary to verify the prospect of comparisons based on geological grounds.

Loading

Article metrics loading...

/content/papers/10.3997/2214-4609.201700300
2017-04-24
2024-03-29
Loading full text...

Full text loading...

References

  1. Bau, M., Dulski, P.
    [1996] Distribution of Yttrium and rare-earth elements in the Penge and Kuruman iron-formations, Transvaal Supergroup, South Africa. Precambrian Research, 79, 37–55.
    [Google Scholar]
  2. Dietrich, R.V., and Skinner, B.J.
    [1979] Rocks and rock minerals. John Wiley & Sons, New York.
    [Google Scholar]
  3. Emery, D., and RobinsonA.
    [1993] Inorganic geochemistry; applications to petroleum geology. London, United Kingdom: Blackwell Scientific Publications, 32–100.
    [Google Scholar]
  4. Frimmel, H. E.
    , [2009] Trace element distribution in Neoproterozoic carbonates as palaeoenvironmental indicator. Chemical Geology, 258, 338–353.
    [Google Scholar]
  5. Gradstein, F. M., Ogg, J. G., Schmitz, M. D. and Ogg, G. M.
    [2012] The geologic time scale 2012. Elsevier Science & Technology, Amsterdam.
    [Google Scholar]
  6. Hjuler, M. L., and Fabricius, I. L.
    [2009] Engineering properties of chalk related to diagenetic variations of Upper Cretaceous onshore and offshore chalk in the North Sea area. Journal of Petroleum Science and Engineering, 68, 151–170.
    [Google Scholar]
  7. Morozova, V., Zimmermann, U., Bertolino, S., Madland, M.V., Tait, J., Hildebrand-Habel, T.
    [2011] Clay and carbonate mineralogy and chemistry of chalk from selected Late Cretaceous rocks. Vinterkonferansen 2011, Norsk Geologisk Forening NGF Abstracts and Proceeedings, 1, 64–65 (Abstract).
    [Google Scholar]
  8. Nozaki, Y., Zhang, J. and Amakawa, H.
    [1997] The fractionation between Y and Ho in the marine environment. Earth and Planetary Science Letters, 148, 329–340.
    [Google Scholar]
  9. Shields, G. A., and Webb, G. R.
    [2004] Has the REE composition of seawater changed over geological time?Chemical Geology, 204(1–2), 103–107.
    [Google Scholar]
  10. Taylor, S.R. and McLennan, S.M.
    [1985] The Composition and Evolution of the Continental- Crust -Rare-Earth Element Evidence from Sedimentary-Rocks: Philosophical Transactions of the Royal Society of London, 301, 381–399.
    [Google Scholar]
  11. Wang, W., Madland, M. V., Zimmermann, U., Nermoen, A., Korsnes, R. I., Bertolino, S. R. A., and Hildebrand-Habel, T.
    [2016]. Evaluation of porosity change during chemo-mechanical compaction in flooding experiments on Liège outcrop chalk. In: Armitage, P. J., Butcher, A. R., Churchill, J. M., Csoma, A. E., Hollis, C., Lander, R. H., Omma, J. E. & Worden, R. H. (Eds) Reservoir Quality of Clastic and Carbonate Rocks: Analysis, Modelling and Prediction. Geological Society, London, Special Publications, 435.
    [Google Scholar]
http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609.201700300
Loading
/content/papers/10.3997/2214-4609.201700300
Loading

Data & Media loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error