Influence of Shale Conductivities on the Electrical Conductivity of Low-Permeability Rocks

Many of the wells now being drilled in the tight gas sands in the western US are using potassium-based drilling muds to help stabilize the clays being encountered. Because of this, there has been some concern that potassium and sodium ions may behave differently in electric logging. In free water, K+ has an equivalent conductance almost 50% greater than the Na+ion at 25 degrees C. The model proposed by Waxman and Smits and the Dual-Water model are most commonly used to explain the conductivity of shaly formations. These models have been used primarily with sodium counterion. These models are examined in this report with data based on the potassium counterion. It was concluded that the data fits both models equally well, although there seems to be somewhat less dependence of the porosity exponent on shaliness with the D-W model.