Down-hole permeability prediction – a chemometric wire-line log feasibility study from a North Sea chalk well

Permeability in chalk depends primarily on porosity but also on other factors such as clay and quartz content, and can theoretically be described by the Kozeny equation using empirically determined constants (Mortensen et al. 1998; Røgen & Fabricius 2002). Recent attempts to predict permeability from wire-line logs have shown that compressional velocity within operative chalk units, defi ned by specifi c surface and hydraulic properties established from stratigraphy and core plugs, can provide excellent well permeability predictions (Alam et al. 2011). High-quality predictions depend on a solid knowledge of a multitude of parameters of the relevant ‘operative rock types’. Th e more detailed this a priori knowledge is, the better predictions can be achieved. But this approach may, or may not, be fast enough for wellsite operations or when core data are lacking. In this study, we illustrate a situation for direct permeability prediction if only well-site, wire-line logs are available. Th is pilot study is based on multivariate descriptor relationships, specifi cally aimed at direct permeability prediction, using all immediately available wire-line characteristics and/or core (plug) information in a top-down mode with sequential exclusion of non-correlated, irrelevant variables. We show prediction-model results based on [log] data only and on [log + plug] data. Other relevant descriptors could be included in an augmented X-matrix, such as quantitative core and facies descriptions while still retaining the fast wellsite perspective. However, such data were not included in this feasibility study.