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Line 168: − + − + − − [[File:charles-l-vavra-john-g-kaldi-robert-m-sneider_capillary-pressure_5.jpg|thumb|{{figure_number|5}}Effect of capillary pressure (left) on water saturation (right). At any given height above the free water level, water saturations vary widely among rock types (A-E) due to diffferences in capillarity. For example, at 50 ft above free water level, water saturations vary from 18% (rock type A) to 95% (rock type E). A well drilled into an interbedded sequence of these rock types would show multiple oil-water contacts and a highly irregular vertical saturation profile. Note also the wide transition zone in rock type B caused by poor sorting of the pore throats.]]
→Additional applications
===Additional applications===
===Additional applications===
Capillary pressure data can also be applied to help distinguish reservoir from nonreservoir and pay from nonpay (see [[Effective pay determination]]). Several workers have attempted to correlate capillary pressure data and brine or air permeabilities. Purcell related capillary pressures empirically to air [[permeability]] through the graphical integral of the curve of mercury saturation versus reciprocal capillary pressure squared. Swanson (1981)<ref name=Swanson_1981>Swanson, R. G., 1981, Sample examination manual:AAPG Methods in Exploration Series, 35 p.</ref> proposed a simple nomograph whose application improved estimation of brine [[permeability]] from capillary pressure measurements on sidewall cores and ditch cuttings.
Capillary pressure data can also be applied to help distinguish reservoir from nonreservoir and pay from nonpay (see [[Effective pay determination]]). Several workers have attempted to correlate capillary pressure data and brine or air permeabilities. Purcell related capillary pressures empirically to air [[permeability]] through the graphical integral of the curve of mercury saturation versus reciprocal capillary pressure squared. Swanson<ref name=Swanson_1981>Swanson, R. G., 1981, Sample examination manual:AAPG Methods in Exploration Series, 35 p.</ref> proposed a simple nomograph whose application improved estimation of brine [[permeability]] from capillary pressure measurements on sidewall cores and ditch cuttings.
Another type of mercury test involves injecting mercury to a saturation less than the maximum, withdrawing the mercury to some residual wetting phase saturation, and then reinjecting the mercury. This process, repeated several times to progressively higher maximum pressures, produces hysteresis loops. These loops, wherein mercury is partially withdrawn and then reinjected, can be used to investigate withdrawal efficiency at various initial saturations (Morrow, 1970<ref name=Morrow_1970>Morrow, N. R., 1970, Irreducible wetting phase saturations in porous media: Chemical Engineering Science, v. 25, p. 1799-1815.</ref>; Melrose and Brandner, 1974<ref name=Melrose_etal_1974>Melrose, J. C., and C. F. Brandner, 1974, Role of capillary forces in determining microscopic displacement efficiency for oil recovery by [[waterflooding]]: Journal Canadian Petroleum Technology, v. 13, p. 54-62.</ref>; Wardlaw and Taylor, 1976<ref name=Wardlaw_etal_1976>Wardlaw, N. C., and R. P. Taylor, 1976, Mercury capillary pressure curves and the interpretation of pore structures and capillary behavior in reservoir rocks: Bulletin of Canadian Petroleum Geology, v. 24, p. 225-262.</ref>; Wardlaw and Cassan, 1978<ref name=Wardlaw_etal_1978>Wardlaw, N. C., and J. P. Cassan, 1978, Estimation of recovery efficiency by visual observation of pore systems in reservoir rocks: Bulletin of Canadian Petroleum Geology, v. 26, p. 572-585.</ref>; Wardlaw et al., 1988<ref name=Wardlaw_etal_1988>Wardlaw, N. C., M. McKellar, and Y. Li, 1988, Pore and throat size distribution determined by mercury porosimetry and by direct observation: Carbonates and Evaporites, v. 3, p. 1-15.</ref>). Results suggest that the higher the initial saturation of the nonwetting phase, the greater the withdrawal efficiency. Porosimetry uses hysteresis loops to interpret pore body and pore throat size distributions and their patial arrangement (Dullien and Dhawan, 1974<ref name=Dullien_etal_1974>Dullien, F. A. L., and G. K. Dhawan, 1974, Characterization of pore structure by a combination of quantitative photomicrography and mercury porosimetry: Journal Colloid and Interface Science, v. 47, p. 337-349.</ref>; Wardlaw et al., 1988<ref name=Wardlaw_etal_1988 />). Pore sizes have also been evaluated with rate-controlled mercury injection (Yuan and Swanson, 1986)<ref name=Yuan_etal_1986>Yuan, H. H., and B. F. Swanson, 1986, Resolving pore space characteristics by rate-controlled porosimetry: 5th Symposium on [[Enhanced oil recovery]] of the Society of Petroleum Engineers and the Department of Energy, April, SPE/DOE 14892, 9 p.</ref>.
Another type of mercury test involves injecting mercury to a saturation less than the maximum, withdrawing the mercury to some residual wetting phase saturation, and then reinjecting the mercury. This process, repeated several times to progressively higher maximum pressures, produces hysteresis loops. These loops, wherein mercury is partially withdrawn and then reinjected, can be used to investigate withdrawal efficiency at various initial saturations.<ref name=Morrow_1970>Morrow, N. R., 1970, Irreducible wetting phase saturations in porous media: Chemical Engineering Science, v. 25, p. 1799-1815.</ref> <ref name=Melrose_etal_1974>Melrose, J. C., and C. F. Brandner, 1974, Role of capillary forces in determining microscopic displacement efficiency for oil recovery by [[waterflooding]]: Journal Canadian Petroleum Technology, v. 13, p. 54-62.</ref> <ref name=Wardlaw_etal_1976>Wardlaw, N. C., and R. P. Taylor, 1976, Mercury capillary pressure curves and the interpretation of pore structures and capillary behavior in reservoir rocks: Bulletin of Canadian Petroleum Geology, v. 24, p. 225-262.</ref> <ref name=Wardlaw_etal_1978>Wardlaw, N. C., and J. P. Cassan, 1978, Estimation of recovery efficiency by visual observation of pore systems in reservoir rocks: Bulletin of Canadian Petroleum Geology, v. 26, p. 572-585.</ref> <ref name=Wardlaw_etal_1988>Wardlaw, N. C., M. McKellar, and Y. Li, 1988, Pore and throat size distribution determined by mercury porosimetry and by direct observation: Carbonates and Evaporites, v. 3, p. 1-15.</ref> Results suggest that the higher the initial saturation of the nonwetting phase, the greater the withdrawal efficiency. Porosimetry uses hysteresis loops to interpret pore body and pore throat size distributions and their partial arrangement.<ref name=Dullien_etal_1974>Dullien, F. A. L., and G. K. Dhawan, 1974, Characterization of pore structure by a combination of quantitative photomicrography and mercury porosimetry: Journal Colloid and Interface Science, v. 47, p. 337-349.</ref> <ref name=Wardlaw_etal_1988 /> Pore sizes have also been evaluated with rate-controlled mercury injection.<ref name=Yuan_etal_1986>Yuan, H. H., and B. F. Swanson, 1986, Resolving pore space characteristics by rate-controlled porosimetry: 5th Symposium on [[Enhanced oil recovery]] of the Society of Petroleum Engineers and the Department of Energy, April, SPE/DOE 14892, 9 p.</ref>
It should be noted that although these more specialized procedures are quite informative, especially for approximating hydrocarbon recovery efficiencies, they are also relatively labor intensive and expensive when compared to routine mercury injection tests.
It should be noted that although these more specialized procedures are quite informative, especially for approximating hydrocarbon recovery efficiencies, they are also relatively labor intensive and expensive when compared to routine mercury injection tests.
==See also==
==See also==