SCA2004-51 1/7 NMR MONITORING OF WATER SATURATION DURING GRAVITY DRAINAGE AND THE DETERMINATION OF WETTING PHASE RELATIVE PERMEABILITY R. Perunarkilli, I. Chatzis, M.A. Ioannidis and C. Lemaire Department of Chemical Engineering, University of Waterloo, Ontario, CANADA This paper was prepared for presentation at the International Symposium of the Society of Core Analysts held in Abu Dhabi, UAE, 5-9 October, 2004 ABSTRACT Free fall gravity drainage experiments were conducted in 110-125 cm long columns of glass beads with 300 µm average particle size and absolute permeability of 100 Darcy. The wetting phase (water) saturation was monitored by proton NMR relaxation. NMR magnetization decay measurements using the CPMG (Carr-Purcell-Meiboom-Gill) pulse sequence were made at three fixed locations within the packed column during the free fall gravity drainage of water. As the bulk water drained with time at a selected location, the proton content decreased and the characteristic proton relaxation rate increased as water was gradually displaced from the larger pores. The NMR measurements thus permitted simultaneous determination of the water saturation S w (t, x) and the characteristic relaxation rate with time t at a fixed location x. NMR measurements at capillary equilibrium conditions were also made to determine the drainage capillary pressure curve for the glass bead packing. Numerical simulations of gravity drainage based on multiphase Darcy’s law were used to test the predictive ability of two models of water relative permeability: an empirical model based on fitting of the capillary pressure data (Van Genuchten, 1980) and a model derived from percolation theory arguments and involving parameters measurable by NMR (Chen et al., 1994). Both models were able to reproduce the experimentally measured water saturation profiles at all three locations within the column, as well as the water production history. Two key conclusions emerge from this work. Firstly, the wetting phase relative permeability for gravity drainage in a homogeneous medium is independent of position. Secondly, the wetting phase relative permeability for gravity drainage in a homogeneous medium can be predicted from a model involving quantities measurable by NMR. The latter conclusion has potentially important implications for the estimation of wetting phase relative permeability. INTRODUCTION Gravity drainage in porous media is important to many industrial processes, including areas of soil physics, oil recovery and ground water hydrology. During gravity drainage it is important to know the distribution of wetting phase and the relative permeability functions of the wetting and non-wetting phase. It is not possible to observe directly and non-destructively the changes taking place in individual pores, however it is possible to make suitable measurements of wetting phase saturation by application of NMR