Valutazione del contributo della porosità effettiva alla trasmissività di acquiferi fratturati con tecniche di laboratorio e di campo

Laboratory and field have been carried out on samples of fractured carbonate rock typical of carbonate formations of the Puglia Region (Southern Italy) in order to characterize the pore space and the resultant aquifer transmissivity. In the lab, both conventional and Magnetic Resonance (MR) techniques were applied to the rock samples taken from deep fractured aquifers. The conceptual schematization of the studied fractured aquifer is a "layered model", made up of a set of parallel fractures, allowed the evaluation of the average fracture aperture on the basis of the MR lab estimation. Modest changes in rock matrix porosity (<0.1%) produce a large variation (>10%) of estimated fracture apertures. The results were confirmed by field test carried out in Puglia aquifers formations. Moreover, the tracer test carried out on the Bari experimental well field site, showed the efficacy of the MR technique and lab methods, based on the analysis of immobile water in the rock matrix and separate micro and macro porosities derived from field test, which is directly correlated to the aquifer transmissivity, allowed a correct fracture aperture estimation and, consequently, the evaluation of immobile water quantity in the ro0ck matrix studied. The quantification of these water volumes, which are very important in solving fluid flow and diffusion problems in fractured aquifers, enhances the efficacy of the lab techniques used for the rock porosity estimations.