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Magnetic resonance and petrophysical characterization of porous media

Keywords: MRR, porous media, permeability, wettability, UPEN
Fig. 1. Magnetic Resonance Tomograph (Esaote, Italy) at the LAGIRN Lab (picture by V. Bortolotti).
Fig. 2. Creation of a T2 relaxation times map of a rock sample (picture by V. Bortolotti).
Fig. 3. T1 relaxation distribution curve; time evolu-tion of the wettability of a rock sample saturated with acid soltrol (picture by V. Bortolotti).

Nuclear Magnetic Resonance Relaxometry (MRR) is a universally accepted technique for the spatially non-resolved determination of structural and transport properties of porous media in a non-destructive and non-invasive way. It is based on parameters like longitudinal and transverse relaxations time (T1 and T2, respectively) and magnetization density (Mo) and, nowadays, is widely used both in core and log analysis to determine petrophysical properties of rocks, such as porosity, pore size distribution, permeability, wettability changes and irreducible water saturation. Natural rocks are usually heterogeneous and this generally leads to multiexponential relaxation, which we have usually inverted by UpenWin software, to obtain the distribution of local Surface/Volume ratios.

UpenWin is a software for Windows internally developed that implements the UPEN (Uniform PENalty) algorithm and is distributed by the University of Bologna. UPEN is a robust algorithm for the inversion of multiexponential decay data, that allows appropriate smoothing of the distribution, allowing sharp peaks without breaking broad features into multiple peaks not required by the data. Magnetic Resonance Imaging (MRI) is a spatially resolved method to get information on the distribution of oil or/and water into the porous medium and to follow flow and absorption of the saturating fluids. A powerful extension of the previous techniques is the Quantitative Relaxation Tomography (QRT), based on the combination of MRR with MRI. QRT generates relaxation time maps, i.e. images where the signal of each voxel (elementary volume, corresponding to the elementary 2D pixel in the image) is proportional to T1 or T2 or Mo of the fluid in that voxel.

The research activity of this group is focalized on the use of both MRR and MRI techniques to characterize the petrophysical properties of the porous media, to monitor the saturating fluids flow and to quantify the interaction of the fluids with the surfaces of the pores space. Particularly studied are the wettability and the permeability of rocks, that mainly affects oil recovery, and natural and amended soils.

Main publications

Bortolotti, V., Fantazzini, P., Mongiorgi, R., Sauro, S., Zanna, S., Hydration kinetics of cements by Time-Domain Nuclear Magnetic Resonance: Application to Portland-cement-derived endodontic pastes. Cement And Concrete Research, 42, 3, 577-582, 2012.

Bonoli, A., Bortolotti, V., Macini, P., Mesini, E., Vannini, M., Natural soil mixed with paper mill sludge characterization by 1h nuclear magnetic resonance longitudinal relaxation time. Proceedings of the CRETE 2012 - 3rd International Conference on Industrial and Hazardous Waste Management, Chania (Crete, GR), September 12-14th, 2012.

Bortolotti, V., Fantazzini, P., Gombia, M., Greco, D., Rinaldin, G., Sykora, S., PERFIDI filters to suppress and/or quantify relaxation time components in multi-component systems: An example for fat-water systems. Journal of Magnetic Resonance, 206, 2: 219 – 226, 2010.

Gombia, M., Bortolotti, V., Brown, RJS, Camaiti, M., Cavallero, L. and Fantazzini, P., Water Vapor Absorption in Porous Media Polluted by Calcium Nitrate Studied by Time Domain Nuclear Magnetic Resonance. Journal of Physical Chemistry B, 113, 31, 10580-10586, 2009.

Gombia, M., Bortolotti, V., Brown, R. J. S., Camaiti, M., and Fantazzini, P., Models of water imbibition in untreated and treated porous media validated by quantitative magnetic resonance imaging. Journal of Appl.Physics, 103, 9, pp 8. 2008.

Bortolotti, V., Gombia, M., Cernich, F., Michelozzi, E., Fantazzini, P., A study to apply nuclear magnetic resonance porosity measurements to seabed sediments. Marine Geology, 230:21–27, 2006.

Bortolotti, V., Camaiti, M., Casieri, C., De Luca, F., Fantazzini, P., Terenzi, C., Water absorption kinetics in different wettability conditions studied at pore and sample scale in porous media by portable single-sided and laboratory imaging devices. Journal of Magnetic Resonance, 181: 287 – 295, 2006.

Bortolotti, V., Campagnoli, A., Gombia, M., Fantazzini, P., Barile, G., Masciopinto, C., Quantitative relaxation tomography (QRT) and field test to estimate a porosity-transmissivity relationship in fractured aquifer. Proceedings of FEM-MODFLOW Conference, September 13-16, Karlovy Vary, Czech Republic, Edited by Karel Kovar, Zbynek Hrkal and Jiri Bruthans, pp 7-10, 2004.

Borgia, G.C., Bortolotti, V., Fantazzini, P. Changes of the local pore space structure quantified in heterogeneous porous media by 1H magnetic resonance relaxation tomography. Journal of Appl. Physics, 90: 1155-1163, 2001.

Borgia, G.C., Bortolotti, V., Fantazzini, P., Magnetic Resonance Relaxation-Tomography to Assess Fractures Induced in Vugular Carbonate Cores. SPE paper 56787, Proceedings of the 74-th Annual Technical Conference and Exhibition of SPE, Houston, 3 - 6  Oct. 1999.

Borgia, G. C., Bortolotti, V., Dattilo, P., Fantazzini P., Maddinelli G., Quantitative determination of porosity: a local assessment by NMR Imaging techniques. Magn. Res. Imaging, 14: 919-921, 1996.

Bilardo, U., Borgia, G.C., Bortolotti, V., Fantazzini, P., Mesini, E., Magnetic resonance lifetimes as a bridge between transport and structural properties of natural porous media. J. Pet. Sc. and Eng., 5: 273-283, 1991.

addinelli. Quantitative determination of porosity: a local assessment by NMR Imaging techniques. Magn. Res. Imaging, 14: 919-921, 1996.

U. Bilardo, G. C. Borgia, V. Bortolotti, P. Fantazzini, E. Mesini. Magnetic resonance lifetimes as a bridge between transport and structural properties of natural porous media. J. Pet. Sc. and Eng., 5: 273-283, 1991.