Dissolution of apatite in North Sea Jurassic sandstones; implications for the generation of secondary porosity

Saved in:
Authors:Morton, A. C.
Author Affiliations:Primary:
Br. Geol. Surv., Keyworth, United Kingdom
Volume Title:Features of mineral diagenesis in hydrocarbon reservoirs
Volume Authors:Harrison, R. K., editor; Morgan, D. J.
Source:Clay Minerals, 21(4), p.711-733; Mineralogical Society, Clay Minerals Group, and Petroleum Exploration Society of Great Britain, joint meeting on Features of mineral diagenesis in hydrocarbon reservoirs, Cambridge, United Kingdom, Apr. 2-4, 1985, edited by R. K. Harrison and D. J. Morgan. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0009-8558
Publication Date:1986
Note:In English. 44 refs.; illus. incl. 1 table, strat. cols., sketch map
Summary:Heavy-mineral studies on Jurassic sandstones from the central and northern North Sea areas and from the Lossiemouth Borehole (onshore NE Scotland) show that the dissolution of apatite is a function of depositional environment rather than burial depth. In the shallow marine Upper Jurassic sands of the Claymore, Clyde and Tartan Fields, and in the deeper-water Magnus sands, apatite is ubiquitous, even where burial depths exceed 3800 m. Conversely, the fluvio-deltaic sands of the Beatrice, Heather, Ninian and Murchison Fields, and of the Lossiemouth Borehole, have suffered apatite dissolution, although burial depths range from very shallow (Lossiemouth Borehole) to about 3300 m. This clearly indicates that apatite dissolution has taken place through penetration of low-pH meteoric groundwaters at a very early stage in diagenesis, and that high-temperature fluids circulating in deep burial have had little or no effect. This is in accord with patterns of mineral dissolution observed in other sedimentary basins and in the North Sea Palaeocene. Although dissolution of heavy minerals is unlikely to generate significant secondary porosity, the process is nevertheless caused by the same pore-fluids that dissolve major framework constituents. Patterns of heavy-mineral dissolution therefore provide clues to the nature of these pore-fluids. Here, the relative stability of apatite is particularly significant. The order of stability apatite > garnet > kyanite, which characterizes deep burial of North Sea sandstones, has previously been simulated experimentally using fluids of pH 8 at room temperature. This suggests that high-temperature acidic pore-fluids may not have played a significant role in the development of secondary porosity in North Sea sandstones. [D.J.M.]
Subjects:Apatite; Bajocian; Brent Group; Clastic rocks; Clay mineralogy; Diagenesis; Economic geology; Electron probe data; Energy sources; Heavy minerals; Indicators; Jurassic; Kimmeridge Clay; Mesozoic; Middle Jurassic; Offshore; PH; Phosphates; Porosity; Reservoir rocks; Sandstone; Sedimentary rocks; Solution; Thermal history; Upper Jurassic; Atlantic Ocean; Europe; Great Britain; North Atlantic; North Sea; Scotland; United Kingdom; Western Europe; Areal studies; Beatrice Field; Claymore Field; Claymore Sandstone Member; Clyde Field; Heather Field; Lossiemouth; Murchison Field; Ninian Field; Piper Formation; Tartan Field
Abstract Numbers:87M/3439
Record ID:1987039782
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
Tags: Add Tag
No Tags, Be the first to tag this record!
Be the first to leave a comment!
You must be logged in first