Geosteering of high-angle wells using heavy mineral analysis: the Clair Field, West of Shetland

Conventionally, a combination of biostratigraphy, logging-while-drilling (LWD) data, and routine cuttings description is used to monitor continually the geology encountered during drilling of high-angle wells. However, the biostratigraphic component of the geosteering tool kit cannot be used if there is insufficient diversity of microfossils in the sequence to be drilled. In such circumstances, alternative, less conventional geosteering methods can be used. This paper presents the application of one such approach, heavy-mineral analysis (HMA), in monitoring high-angle wells in the Clair field, west of Shetland, U.K. The reservoir sequence in the Clair field comprises Devonian-Carboniferous nonmarine fluvial and eolian sandstones that lack a continuous, diverse suite of palynomorphs. Consequently, there is no high-resolution biostratigraphic framework for reservoir correlation. By contrast, heavy minerals occur throughout the sequence and therefore offer a potential for correlation and discrimination of different sandstone units.