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Line 37: − − If a liquid wets a surface, it tends to spread and cover that surface. Observed on a microscopic scale, the edge of the liquid has a characteristic shape. A knife edge shape indicates wetting, while a beaded edge shape indicates nonwetting. This is shown quantitatively in Figure 1, which shows a drop of water surrounded by oil and contacting a solid surface. If the edge of the drop forms an acute angle (θ<sub>e</sub> 5.) + Line 70:
Line 69: − − [[file:wettability_fig2.png|thumb|{{figure number|2}}Combined Amott and USBM method. (After <ref name=pt05r14>Anderson, W. G., 1986b, Wettability literature survey—Part 2, Wettability measurements: Journal of Petroleum Technology, v. 38, p. 1246–1262., 10., 2118/13933-PA</ref>; from <ref name=pt05r143>Shamra, M. M., Wundlerlich, R. W., 1985, The alteration of rock properties due to interactions with [[drilling fluid]] components: Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, Las Vegas, NV, Sept. 22–25, SPE 14302.</ref>.)]] Line 132:
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→Techniques
===Contact angle measurements===
===Contact angle measurements===
[[file:wettability_fig1.png|thumb|{{figure number|1}}Wettability of oil, water, and rock system. (After <ref name=pt05r134>Raza, S. H., Treiber, L. E., Archer, D. L., 1968, Wettability of reservoir rocks and its evolution: Producers Monthly, v. 32, p. 2–7.</ref>.)]]
[[file:wettability_fig1.png|thumb|{{figure number|1}}Wettability of oil, water, and rock system. (After <ref name=pt05r134>Raza, S. H., Treiber, L. E., Archer, D. L., 1968, Wettability of reservoir rocks and its evolution: Producers Monthly, v. 32, p. 2–7.</ref>.)]]
If a liquid wets a surface, it tends to spread and cover that surface. Observed on a microscopic scale, the edge of the liquid has a characteristic shape. A knife edge shape indicates wetting, while a beaded edge shape indicates nonwetting. This is shown quantitatively in [[:file:wettability_fig1.png|Figure 1]], which shows a drop of water surrounded by oil and contacting a solid surface. If the edge of the drop forms an acute angle (θ<sub>e</sub> 5.)
Several techniques used to measure this angle are described by Adamson<ref name=pt05r2 />. The measurements are generally made on a polished surface that simulates the reservoir material. For sandstones, glass slides or polished quartz are often used. Polished marble is usually chosen to simulate a carbonate reservoir. An adaptation of the technique uses a drop of liquid confined between two surfaces<ref name=pt05r39>Craig, F. F., 1971, The reservoir engineering aspects of waterflooding: Dallas, TX, Society of Petroleum Engineers Monograph No. 3, 120 p.</ref>.
Several techniques used to measure this angle are described by Adamson<ref name=pt05r2 />. The measurements are generally made on a polished surface that simulates the reservoir material. For sandstones, glass slides or polished quartz are often used. Polished marble is usually chosen to simulate a carbonate reservoir. An adaptation of the technique uses a drop of liquid confined between two surfaces<ref name=pt05r39>Craig, F. F., 1971, The reservoir engineering aspects of waterflooding: Dallas, TX, Society of Petroleum Engineers Monograph No. 3, 120 p.</ref>.
:<math>\mbox{Index} = \overline{BC}/\overline{BD} - \overline{DE}/\overline{DB}</math>
:<math>\mbox{Index} = \overline{BC}/\overline{BD} - \overline{DE}/\overline{DB}</math>
The range of values and the corresponding wettability characteristics are listed in Table 1.
The range of values and the corresponding wettability characteristics are listed in Table 1.
===USBM method===
===USBM method===
[[file:wettability_fig2.png|thumb|{{figure number|2}}Combined Amott and USBM method. (After <ref name=pt05r14>Anderson, W. G., 1986b, Wettability literature survey—Part 2, Wettability measurements: Journal of Petroleum Technology, v. 38, p. 1246–1262., 10., 2118/13933-PA</ref>; from <ref name=pt05r143>Shamra, M. M., Wundlerlich, R. W., 1985, The alteration of rock properties due to interactions with [[drilling fluid]] components: Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, Las Vegas, NV, Sept. 22–25, SPE 14302.</ref>.)]]
The USBM method developed by Donaldson et al.<ref name=pt05r47 /> uses the same types of data, but considers the work required to do the forced displacement. This requires calculating the area under the [[capillary pressure]] curve obtained during the forced displacement. Generally, the capillary pressure displacement is done by centrifuging, but other capillary displacement techniques can be used.
The USBM method developed by Donaldson et al.<ref name=pt05r47 /> uses the same types of data, but considers the work required to do the forced displacement. This requires calculating the area under the [[capillary pressure]] curve obtained during the forced displacement. Generally, the capillary pressure displacement is done by centrifuging, but other capillary displacement techniques can be used.
:<math>W = \log \frac{A_{1}}{A_{2}}</math>
:<math>W = \log \frac{A_{1}}{A_{2}}</math>
The Amott and the USBM methods can be combined into a single test<ref name=pt05r143 />. This combination and the capillary pressure plot used in the USBM calculation, are shown in Figure 2.
The Amott and the USBM methods can be combined into a single test<ref name=pt05r143 />. This combination and the capillary pressure plot used in the USBM calculation, are shown in [[:file:wettability_fig2.png|Figure 2]].
===Comparison of the two methods===
===Comparison of the two methods===