Review of Existing Shaly Sand Evaluation Models And Introduction of a New Method Based On Dry Clay Parameters Available to Purchase

Shaly sand evaluation remains a kind of enigma even after more than half a century of research and field applications. This paper offers a convenient way to compare the Archie, Modified Simandoux, Dual Water, Waxman Smits, Indonesian, Juhasz and a novel Difference method. The two main groups of shaly sand evaluations are based on shale conductivity and cation exchange capacity respectively. They can be linked via the bound-water saturation. This parameter was selected, because it is the bound-water that produces the additional conductivity. The objective of the study is to highlight major differences & similarities, but not to find the best method. A field study demonstrates that a judicious selection of input parameters produces water saturation profiles that almost overlay for most methods. Parameters such as shale conductivity, shale density, and cation exchange capacity, were selected well within reasonable ranges of uncertainty to obtain this agreement. For the latter the shale density is critical, because it is related to the bound-water conductivity leading to discrepancies of more than 10% in saturations. It is recommended to use the bound-water conductivity and temperature relation given in Clavier's Dual Water paper. An unexpected result was that the Modified Simandoux model, designed for effective porosity, gave saturations close to the other methods when total porosity is used. The Indonesian method is the odd one out, and could not be reconciled with other methods. The Juhasz and Waxman Smits methods are most sensitive to the cation exchange capacity, and the Juhasz method also to the shale neutron porosity. This study introduces a new method that alleviates this dependency by using both dry clay and shale parameters. This is particularly attractive when the clay type is determined on rock samples, because the dry properties, in contrast with wet clay properties, are readily available.