Application Of Cation Exchange Capacity In A Study Of The Shannon Sand Of Wyoming

Downhole log data are utilized with laboratory determined cementation exponents, saturation exponents and cation exchange capacities to furnish improved values of reservoir water saturation in the Shannon Sand of the Teapot Dome field. Shaly sand effects are important in this reservoir. Significant errors result in calculated water saturations, and hence oil-in-place if clean sand analysis techniques are utilized and shale effects are ignored. Waxman-Smits-Thomas equations were employed in this study. Examples present a calculation format, outline of procedures and illustrate the calculation of F*, m*, a* and n* by combining the laboratory electrical property data with measured cation exchange capacities. Also shown are the effects of several incorrect procedures to be avoided when utilizing the Waxman-Smits-Thomas approach. These include combination of the cation exchange data with a non-applicable formation factor-porosity relationship, use of a improper water resistivity when calculating F*, m*, a*and n* from laboratory tests, and improper use of porosity and grain density data generated on a core dried with controlled humidity in order to leave two molecular layers of water on the clay surfaces.