Abstract:
An extensive set of conventional and special core analysis measurements, complemented by additional chemical and mineralogical analyses was performed, forming the basis for the evaluation of the complex thin bedded gas-bearing shaly-sand formations of Miocene age in the Carpathian Foredeep region of Southern Poland. Mineralogy was established by using full elemental composition, XRD method, total surface area and cation exchange capacity (CEC). The analysis showed that the most important clay component is illite – smectite mixed layer. Statistical multivariate analysis of all data helped to set up a comprehensive general petrophysical model. For the notoriously difficult CEC information for the rock matrix we could establish a reliable correlation (corr. coefficient r2 around 0.95) between thermal neutron absorption cross section SIGMA and total natural radioactivity GR with CEC, with boron and rare earth elements the two most important SIGMA contributors in the rock matrix. This good correlation permits a continuous on-line CEC determination and therefore a reliable application of the Waxman-Smits water saturation model to properly take into account the clay mineral effects in evaluating water saturation.
