Determination of effective porosities by the two-well pulse method

Abstract

Results obtained in the use of the two-well pulse method in fissured and granular media are presented. The measurements in the former were aimed mainly at obtaining the effective porosity of Zn-Pb and sulphur deposits in limestone and dolomite formations. Breakthrough curves obtained in these fissured and cavernous formations appeared to be rather regular though highly asymmetrical, due to a high dispersion. Both manual and computer interpretations have been developed on the basis of a new, analytical solution of the dispersion equation. This solution is exact in a unidimensional flow, and approximate in a radial flow. The manual interpretation is based on an assumption of equal surfaces under both theoretical and experimental curves and fitting at a guess, whereas the computer interpretation is based on minimizing the chi-squared value. Some experiments could be interpreted only under an assumption of a breakthrough curve consisting of two or more component breakthrough curves. However, the interpretation is not always unambiguous because in cases of a high dispersion the tail part of the breakthrough curve is seldom measurable. In granular media of fluvial and fluvio-glacial origin usually irregular, though less dispersed, curves were observed. Their interpretation was performed either by a rough approximation or by calculating the mean arithmetic time as the ratio of the first to zero moments. (author)