Adsorption and Flow of Multiple Tracers in Porous Media

Abstract

Abstract It is common practice to employ radioactive tracers for studying fluid movement in oil reservoirs. In many instances, excessive tracer adsorption and anomalous tracer flow behaviour have been reported. The present investigation was concerned with the phenomena associated with the flow of fluids containing radioactive tracers (tritium and Carbon-14). Miscible displacements were conducted in order to evaluate tracer retention and/or adsorption effects. A suitable counting and efficiency determination technique was developed in order to evaluate the radioactivities of fluid systems containing two radioisotopes. The use of two radioactive tracers to trace the simultaneous flow of two fluids was found to be a very effective tool. The adsorption of tritium during miscible displacements conducted in Berea sandstone cores averaged 1.5 per cent. A systematic investigation showed that this adsorption could be explained on the basis of the exchange of tritium atoms with the hydrogen atoms of the water of hydration found in naturally-occurring clays in porous media. It was found that the adsorption of tritium increased with a decrease in the displacement rate. No adsorption of Carbon-14 was observed in miscible displacements in sandstone cores. An average of 0.47 per cent tracer retention was observed during desorption displacements involving Carbon-14, but such retention is attributed to mass transfer effects, and is not considered a true adsorption phenomenon. A technique for determining the counting efficiency of multiply-tagged fluids was developed. The quenching and scintillating effects of a salt, a hydrocarbon and an alcohol were investigated. It was found that liquid scintillation instrument counting efficiency corrections only partially compensate for extraneous quenching or scintillation effects.