Empirical Measures of Wettability in Porous Media and the Relationship between Them Derived From Pore-Scale Modelling |
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Authors: | Dixit A B Buckley J S McDougall S R Sorbie K S |
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Institution: | (1) Department of Petroleum Engineering, Heriot-Watt University, Edinburgh, Scotland, U.K;(2) Petroleum Recovery Research Center, New Mexico Tech, Socorro, NM, U.S.A |
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Abstract: | The wettability of a crude oil/brine/rock system is of central importance in determining the oil recovery efficiency of water displacement processes in oil reservoirs. Wettability of a rock sample has traditionally been measured using one of two experimental techniques, viz. the United States Bureau of Mines and Amott tests. The former gives the USBM index, I
USBM, and the latter yields the Amott–Harvey index, I
AH. As there is no well-established theoretical basis for either test, any relationship between the two indices remains unclear.Analytical relationships between I
AH and I
USBM for mixed-wet and fractionally-wet media have been based on a number of simplifying assumptions relating to the underlying pore-scale displacement mechanisms. This simple approach provides some guidelines regarding the influence of the distribution of oil-wet surfaces within the porous medium on I
AH and I
USBM. More detailed insight into the relationship between I
AH and I
USBM is provided by modelling the pore-scale displacement processes in a network of interconnected pores. The effects of pore size distribution, interconnectivity, displacement mechanisms, distribution of volume and of oil-wet pores within the pore space have all been investigated by means of the network model.The results of these analytical calculations and network simulations show that I
AH and I
USBM need not be identical. Moreover, the calculated indices and the relationship between them suggest explanations for some of the trends that appear in experimental data when both I
USBM and I
AH have been reported in the literature for tests with comparable fluids and solids. Such calculations should help with the design of more informative wettability tests in the future. |
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Keywords: | Wettability USBM index Amott index wetting tests pore-scale modelling network model |
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