An Improved Waxman-Smits Model For Interpreting Shaly Sand Conductivity At Reservoir Conditions Available to Purchase

This paper presents an improved Waxman-Smits shaly sand conductivity model which covers two new aspects of shaly sand conductive characteristics at reservoir conditions. These are the effect of temperature on the equivalent conductance of clay counter-ions and the influence of clay distribution on shaly sand conductivity. This improved Waxman-Smits model is based on the experimental results obtained from over 40 reservoir, synthetic and outcrop rock samples. A new technique developed in this study enables us to make synthetic shaly rock samples with various clay type, content and distribution mode. A novel multi-sample high temperature and high pressure rock testing system is used to measure the electrical conductivity of shaly samples at simulated reservoir conditions. After comparing some significant shaly sand conductivity models with the experimental results obtained, it is concluded that both the Waxman-Smits and Dual-Water shaly sand conductivity models apply adequately at room conditions to homogeneous samples with dispersed clays which are uniformly distributed. For other day distributions and for shaly sands at elevated temperatures, however, these well-known shaly sand conductivity models require modification. The modified version of the Waxman-Smits model proposed in this paper includes a temperature coefficient (?) for the equivalent counter-ion conductivity associated with clay, which is a function of temperature and clay content, and a clay distribution coefficient (?) for the clay content (Qv). The values for ? as a function of temperature and clay content are determined experimentally from multiple-salinity measurements at various temperatures. The clay distribution coefficient (?) is a function of clay distribution mode and the degree of clay mineral concentration and is quantified based on a 3D pore space petrophysical model. The practical application of this improved Waxman-Smits shaly sand conductivity model enhances the accuracy of the estimation of in situ porosity and hydrocarbon saturation of shaly formations from wireline log data.