A Pragmatic Approach to Exploration Petrophysics in Lacustrine Shales

Abstract

The thick, regionally extensive lacustrine shales of the Cooper Basin were discovered more than half a century ago but it wasn't until recently that the source rock and reservoir potential of the shales were recognised, particularly within the Nappamerri Trough which is the deepest and largest of the structural troughs in the Cooper Basin, South Australia. In 2010, at the commencement of an extensive exploration and evaluation program, there were no pre-existing analogues for the Nappamerri Trough shale play as all commercially produced shale plays in North America involve marine rather than lacustrine shales. Data from existing wells in the area provided a preliminary indication of shale potential, in particular the organic content, maturity, mineralogy and extent of overpressure. A thorough wireline logging and core analysis program was designed for the initial exploration wells to expand on the understanding of key shale characteristics. The high geothermal gradient proved to be challenging for evaluation with some logging runs having to be curtailed. As a starting point, published methods for evaluating shales were applied to the Nappamerri Trough shales with limited success. Using a deterministic interpretation method and core calibration, petrophysical evaluations were completed which were not only suitable for initial shale assessment but also identified where the key petrophysical uncertainties were and how they could be addressed in the future.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015