Feasibility of in situ elemental analysis in mudrock evaluation

Abstract

Abstract Geochemical logging now offers the possibility of performing quantitative in situ elemental analysis. Laboratory measurements of element abundances on selected sections of mudrocks were made to simulate the potential use of data available from geochemical logging. The analyses centre on mudrocks from the Magnus Field (North Sea) and Dorset Kimmeridge Clay Formation sequences (Southern England). Subsequent multivariate statistical processing of these analyses showed that pre-defined units within the sections studied can be distinguished geochemically without recourse to mineralogical description. This is demonstrated firstly by cross plotting elemental abundances to pick out significant sympathetic trends and thereafter by clustering and factor analysis techniques which utilize a more extensive dataset. This study shows that the direct application of statistical tests to raw element abundances determined downhole is an appropriate methodology by which conventionally impractical topics, such as the subsurface discrimination of mudrock facies, may be tackled. This conclusion will, no doubt, be tested further as geochemical logging develops over the next few years.