Radioactivity of drilling cuttings from shale resources of the lower paleozoic Baltic Basin

Fractionated drilling wastes originating from shale gas exploration in the Baltic Basin in Polish Pomerania were subjected to measurements of mean activity concentrations of naturally occurring radioactive materials (NORMs). X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were used to understand the rock structure and texture. The activity concentration of radionuclides in bulk wastes and fractionated samples (latter obtained through a sieve analysis) was analyzed by using a gamma-ray spectrometer. After fractionation, three different size ranges were distinguished. Radiological indices were estimated by comparison with the levels recommended by the International Association of Oil and Gas Producers (OGP) and an equivalent absorbed dose was determined with respect to appropriated disposal of cuttings. The results showed that the drilling cuttings from the Ordovician period have a natural radioactivity level comparable to other rocks with the same lithology (potassium K-40 800-992 Bq/kg and thorium Th-232 23.3-30.8 Bq/kg) and they did not exceed acceptable levels of the total absorbed dose rate. The average absorbed dose rate in outdoor air one meter above the drilling cuttings was 54.1 nGy/h. The relation between particle size and natural radioactivity indicated that the concentration of radionuclides increased as the fractions size decreased.