Diffusion of Water at Low Saturation Levels into Sandstone Rock Plugs Measured by Broad Line Magnetic Resonance Profiling
✍ Scribed by P.J. McDonald; T. Pritchard; S.P. Roberts
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 144 KB
- Volume
- 177
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
nique permit direct spatially resolved measurement of flow Broad line magnetic resonance imaging has been used to profile velocities (5) and bulk measurements of self-diffusion coefwater ingress into a series of well-characterized sandstone rock ficients (6). As a result, a considerable literature now exists plugs at saturation levels below the vapor percolation threshold. on the subject. However, almost without exception, applica-The diffusion process has been found to be strongly anomalous. tions to date of MRI applied to reservoir rock plugs have Rather, it is in quantitative agreement with a model based on concentrated on mapping relatively mobile fluid found at parallel transport of water in the vapor phase and adsorbed on the high local saturation levels of the rock. This is because conpore surfaces with the vapor and pore surface water maintained in ventional MRI methods can only be successfully applied to dynamic local equilibrium. Among other parameters, the analysis systems with relatively narrow magnetic resonance spectral has yielded estimates of the surface water diffusion coefficients (mean 5 1 10 06 cm 2 s 01 ) and of the critical depths of surface linewidths equivalent to nuclear spin-spin relaxation times water below which the vapor pressure is substantially reduced by in excess of typically 1-5 ms. There are various mechanisms strong adsorption (mean 30 molecular layers). A temperatureby which the nuclear spin-spin relaxation time of water and dependent study of one plug has shown that the pore surface water oil in rocks can fall substantially below this value. First, diffusion is thermally activated and is governed by an Arrhenius restricted motion in the confined geometry of the pore space rate law with an activation energy of 49 kJ mol 01 . ᭧ 1996 Academic leads to broadening of the resonance by the nuclear dipole-Press, Inc.