Field investigation with regard to the impermeability of clay formations
This report deals with a tentative study for the detection of the secondary permeability in clay formations conducted in several sedimentary basins in central Italy, using geochemical methods. The main purposes are to try a geochemical method, based on the distribution of deep origin gases in soil gas (4He and 222Rn), to detect buried fault systems and to study the permeability of clay as a potential migration pathway for nuclides of radioactive waste deposits, and also to verify the effectiveness of this method for the selection of suitable sites for radwaste disposal. Investigations concerned sedimentary basins filled by sand-clay formations 1000-2000 metres thick and characterised by different tectonics: Era and Chiani-Paglia Valleys (Tuscany and North Latium), structural trenches due to extensive tectonics along the Tyrrhenian edge, and Vasto region, a basin in the Adriatic foretrench, characterised by compressive tectonics. The investigated areas are near or directly correspond to geothermal fields or to hydrocarbon reservoirs supplying gases which may migrate upward along fractures. The results show that the observed helium anomalies are distributed or elongated according to the main tectonic features of the substratum; the magnitude of anomalies seems to correlate with the nature of the deep gas reservoir. The observations seem to confirm that the presence of deep origin gases in soils is controlled by tectonics. Clay thickness does not significantly control the uprising of deep gases: in fact a few metres of unfractured clay can constitute an efficient barrier even to the migration of the most mobile element (He).
Bibliographic Reference: EUR 14585 EN (1993) 61 pp., FS, ECU 8.50
ISBN: ISBN 92-826-5820-1
Record Number: 199310809 / Last updated on: 1994-11-29
Original language: en
Available languages: en