LOW-CONTRAST SECONDARY IMBIBITION IN LONG ROCK CORES

The chemical-shift-resolved N.M.R. imaging method developed by Horsfield et al. 10,11 for quantification of two-phase saturations in permeable rock samples exhibiting broad spectral lines is applied to the observation of secondary imbibition processes in long rock cores. Time-lapsed, semi-quantitative water saturation profiles are obtained during a secondary imbibition in a moderate permeability (< 0.028-mu-m2) limestone exhibiting imperfectly resolved aqueous and hydrocarbon proton resonances. Imaging of a core 30 cm long, in a magnet with a nominal 5 cm diameter spherical volume usable for chemical shift imaging, is accomplished by multiple image acquisition and overlapping segmentation of the desired field of view. Local B0 field correction is achieved by analysis of a Dixon opposed-phase image 5 by the phase-slope method. 2 Although vulnerable to failure where the aqueous and hydrocarbon saturations are nearly balanced, successful observations are made of secondary imbibition fronts of low water-oil contrast where the water saturation may cross 0.5.