The study of clay component conductivity during resistance measurements of core samples and further evaluation of cation exchange capacity by log data interpretation

New core analysis methods are presented for R w , formation water resistivity, and Q v , cation exchange capacity per unit pore volume.Accurate R w values are needed for all resistivity-based water saturation models.Representative values of the rock property Q v are necessary for Q v -based shaly sand models such as Waxman-Smits-Thomas and Dual-Water.Traditional core analysis methods for R w and Q v in shaly tight gas sands are limited and tend to be inaccurate or impractical due to the clay-bound water, extensive cementation, and very low permeability that characterize these formations.The new methods address the influence of clay-bound water on results and include its quantification by nuclear magnetic resonance techniques.They are designed to overcome the limitations and inaccuracies of the traditional methods, particularly with respect to tight gas sands, and result in practical approaches for R w and Q v .Additionally, an improved and unifying equation is presented for the shaly sand parameter B, the counter-ion conductance term found in the Waxman-Smits-Thomas model.Effective use of this model includes application of representative B values for both the laboratory and reservoir environments.Standard sources of B for each environment are identified and standard values are compared to those provided from published equations.The poor and biased comparisons lead to development of a single equation with results that compare more favorably with the reservoir-environment standard and exactly with the laboratory-environment standard.