Gamma-Ray Analysis for U, Th, and K on Bulk Cutting Samples from Deep Wells in the Danish Subbasin and the North German Basin

B. Leth Nielsen, Leif Løvborg, P. Sørensen, E. Mose

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    Abstract

    A total of 1329 bulk cutting samples from deep wells in Denmark were analysed for U, Th and K by laboratory gamma-ray analysis. Contamination of the samples by drilling mud additives, mud solids and fall down was studied by means of a wash down experiment and by comparison with the total gamma-ray response from wireline logging. It is concluded that the inorganic geochemistry on bulk cutting samples must be applied with great caution. The data are useful for geochemical characterization of well sections and for regional geochemical correlation. Radioelement abundance logs and radioelement ratio logs are presented from 3 wells in the Danish Subbasin and 2 wells in the North German Basin. The radioelement geochemistry is discussed for the successive lithostratigraphical units ånd a reference radio element profile is established for the central part of the Danish Subbasin. Finally, a model describing the relationship between common lithofacies and their U content and Th/U ratio is
    suggested. The model deliniates the depositional environment and the relative distances to the provenance areas. It is concluded that

    1) Uranium is mobile during deposition, but since then it is fixed by stable mineral phases at depth.

    2) Thorium reflects source area characteristics and that any available ions are readily adsorped by clay minerals. Thorium anomalies may thus serve as lithostratigraphical markers.

    3) Potassium occurs in unstable rock forming mineral phases. The present distribution is controlled not only by the clastic mineral assemblage, but also by the diagenetic processes through geologic time.
    Original languageEnglish
    Place of PublicationRoskilde
    PublisherRisø National Laboratory
    Number of pages82
    ISBN (Print)87-550-1323-6
    Publication statusPublished - 1987
    SeriesRisø-M
    Number2646
    ISSN0418-6435

    Keywords

    • Risø-M-2646

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