A Core-Log Study of the Hartselle Sandstone in North Alabama With Emphasis in Log Interpretation Problems in Tight Gas Sands

Abstract

The correlations among the physical properties of core samples taken from the Hartselle Sandstone formation were examined, porosity, permeability, formation factor, cementation factor, saturation exponent, caly mineralogy and cation exchange capacity were determined. Constants such as, a, a*, m, m*, n, n* and no were found to be unique and significantly different from those for normal shaly sands. The cation exchange capacities (CEC) were determined by the strontium exchange technique. The curvelinear equation correlating CEC vs. Gamma Ray has been proven to be useful for the prediction of CEC for the Hartselle Sandstone. It has been found that water saturation calculation using Dual-Water and Waxman-Smits models are very sensitive to the values of m*, n* and the clay content, particularlly when water saturation excees 50 percent and Vsh exceeds 15 percent. Therefore accurate determination of these constants is necessary. It was also found that Fertl-Hamm ck equation can be used as a suitable alternative for the tight gas sands, with an accuracy similar to Waximan-Smits model, when the core data is not available