The case of the missing clay, aluminium loss and secondary porosity, South Brae oilfield, North Sea

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Authors:McLaughlin, O. M.; Haszeldine, R. S.; Fallick, A. E.; Rogers, G.
Author Affiliations:Primary:
University of Glasgow, Department of Geology, Glasgow, United Kingdom
Scottish Universities Research and Reactor Centre, United Kingdom
Volume Title:Issue devoted to papers read at a conference on Diagenesis, overpressure and reservoir quality
Volume Authors:Bain, D. C., editor; Hall, P. L.; Shaw, H. F.; Spears, D. A.
Source:Clay Minerals, 29(4), p.651-663; Diagenesis, overpessure and reservoir quality, Cambridge, United Kingdom, March 26, 1993, edited by D. C. Bain, P. L. Hall, H. F. Shaw and D. A. Spears. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0009-8558
Publication Date:1994
Note:In English. 31 refs.; illus., incl. 2 tables, sketch maps
Summary:Upper Jurassic sandstones of the South Brae Field were deposited as a submarine fan complex. The earliest formed concretionary ferroan calcite cement passively encloses detrital feldspars which originally formed more than 10% of the rock. Later non-ferroan calcite at the concretion margins was precipitated from a more aggressive fluid. This fluid dissolved up to half of the feldspars and micas originally present, but little or no clay was precipitated. Aluminium must have been lost from the system. A late dissolution event has enhanced porosity by up to 8%. Feldspar was again reduced in volume by about half, leaving only ∼2% in the rock today. Very minor amounts of fibrous illite and kaolinite (<1%) form the last diagenetic cement. Aluminium must have again been lost from the system. As the Kimmeridge Clay Formation (KCF) encloses and interdigitates with the South Brae sandstones, a local source of organic acids is quite possible. These acid solutions may have increased the mobility of Al. The Al from the feldspars must have therefore been transported vertically into the KCF, or more probably transported laterally by compactional flows out of the basin (up to 10 km) during release of overpressured basinal water. [R.E.S.]
Subjects:Aluminum; Case studies; Clastic rocks; Clay minerals; Jurassic; Mesozoic; Metals; Oil and gas fields; Petroleum; Porosity; Reservoir rocks; Sandstone; Sedimentary rocks; Sheet silicates; Silicates; Upper Jurassic; Atlantic Ocean; North Atlantic; North Sea; Viking Graben; Fladen Ground Spur; South Brae Field
Coordinates:N580000 N590000 E0010000 E0000000
Abstract Numbers:95M/3634
Record ID:1995025469
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
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