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[[Natural gas]] can dissolve in water to a significant enough degree that diffusion through water in the [[seal]] rock can result in substantial loss of gas, given geological time. Because of their very low [[Wikipedia:Solubility|solubility]] in water, [[black oil]]s and high [[Wikipedia:Molecular mass|molecular-weight]] components of oil cannot leak by this mechanism, even at high temperatures.<ref name=ch11r23>McAuliffe, C., D., 1980, [http://archives.datapages.com/data/specpubs/geochem1/data/a029/a029/0001/0050/0089.htm Oil and gas migration: chemical and physical constraints], in Roberts, W., Cordell, R., eds., Problems of Petroleum Migration: AAPG Studies in Geology 10, p. 89–108.</ref> Leakage rates determined in various published studies demonstrate the likelihood of gas accumulations lasting for tens to hundreds of million years (e.g., Motel et al.<ref name=ch11r26>Montel, F., Caillet, G., Pucheu, A., Caltagirone, J., 1993, Diffusion model for predicting reservoir gas losses: Marine and Petroleum Geology, vol. 10, p. 51–57., 10., 1016/0264-8172(93)90099-E</ref>

[[Natural gas]] can dissolve in water to a significant enough degree that diffusion through water in the [[seal]] rock can result in substantial loss of gas, given geological time. Because of their very low [[Wikipedia:Solubility|solubility]] in water, [[black oil]]s and high [[Wikipedia:Molecular mass|molecular-weight]] components of oil cannot leak by this mechanism, even at high temperatures.<ref name=ch11r23>McAuliffe, C., D., 1980, [http://archives.datapages.com/data/specpubs/geochem1/data/a029/a029/0001/0050/0089.htm Oil and gas migration: chemical and physical constraints], in Roberts, W., Cordell, R., eds., Problems of Petroleum Migration: AAPG Studies in Geology 10, p. 89–108.</ref> Leakage rates determined in various published studies demonstrate the likelihood of gas [[accumulation]]s lasting for tens to hundreds of million years (e.g., Motel et al.<ref name=ch11r26>Montel, F., Caillet, G., Pucheu, A., Caltagirone, J., 1993, Diffusion model for predicting reservoir gas losses: Marine and Petroleum Geology, vol. 10, p. 51–57., 10., 1016/0264-8172(93)90099-E</ref>

==Predicting leakage==

==Predicting leakage==

Only gas accumulations can be destroyed by diffusive leakage. For most seal lithologies, loss by diffusion is very slow; so most gas accumulations are preserved for tens to hundreds of millions of years. Rates of loss have been modeled,<ref name=ch11r26 /> but data necessary to quantitatively predict accumulation preservation at a particular prospect are difficult to acquire.

Only gas [[accumulation]]s can be destroyed by diffusive leakage. For most seal lithologies, loss by diffusion is very slow; so most gas accumulations are preserved for tens to hundreds of millions of years. Rates of loss have been modeled,<ref name=ch11r26 /> but data necessary to quantitatively predict [[accumulation]] preservation at a particular prospect are difficult to acquire.

Diffusive leakage is favored by high temperature, high pressure, and a thin, porous seal. Older accumulations are more likely to be destroyed by this process, and late [[Cenozoic]] accumulations are not likely to be destroyed by this process.

Diffusive leakage is favored by high temperature, high pressure, and a thin, porous seal. Older accumulations are more likely to be destroyed by this process, and late [[Cenozoic]] accumulations are not likely to be destroyed by this process.