A recommendation -
of geochemical correlation in barren sedimentary sequences

A significant percentage of hydrocarbon reservoirs are located in sequences, which have poor stratigraphic control. In such cases, correlation can be established from geophysical logs. However this approach is frequently barren, particularly if the sequences shows repetitious geophysical log characteristics. To increase stratigraphic control, recent research has been applied in geochemistry. Results, including this study, demonstrated that major- and trace element geochemistry and heavy-mineral microscopy could be applied to characterise and correlate sequences on a local to regional scale. The success of identifying geochemical fingerprints relies on the fact that the inorganic geochemistry of sediments is highly variable and is sensitive to subtle changes in provenance. However, this study demonstrated that even, apparently uniform successions derived from a most likely single source area show primary differences in the chemistry of their constituent minerals, especially in the composition of accessory minerals. This ability of subtle geochemical variation enables characterisation of succession to be subdivided and correlated between wells. It can also be used to reconstruct sediment paleoflow trends and to identify sediment source areas.

As little as 0.25 - 1g of sediment, which must be carefully picked from either the cores or cuttings are sufficient for geochemical analyse by either XRF or ICP-AES/MS. The heavy-mineral analysis depend on samples of approximately <10g of sediment, to reveal a satisfactory amount of representatives.

In the North Sea, i.e. the Balder- or Sleipner Øst field, the ambiguity and uncertainty of stratigraphic control associated with more traditional methods of correlation such as lithostratigraphy, biostratigraphy and geophysical logging is severe. Thus, it is particularly recommendable to apply geochemical correlation techniques in such barren sedimentary sequences, where this method may provide a substantial contribution to advance the correlation between wells, reconstruct paleoflow trends and to identify source areas.