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| ===Contact angle measurements=== | | ===Contact angle measurements=== |
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− | 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.)
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| [[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>.)]] |
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| + | 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>. |
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| :<math>\mbox{Index} = \overline{BC}/\overline{BD} - \overline{DE}/\overline{DB}</math> | | :<math>\mbox{Index} = \overline{BC}/\overline{BD} - \overline{DE}/\overline{DB}</math> |
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− | [[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>.)]]
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| 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. |
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| ===USBM method=== | | ===USBM method=== |
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| + | [[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>.)]] |
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| 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. |
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| :<math>W = \log \frac{A_{1}}{A_{2}}</math> | | :<math>W = \log \frac{A_{1}}{A_{2}}</math> |
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− | 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]]. |
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| ===Comparison of the two methods=== | | ===Comparison of the two methods=== |