Changes

==Slug flow in primary migration==

==Slug flow in primary migration==

Slug flow (or bulk phase flow) is generally accepted as the dominant mechanism of primary hydrocarbon migration. Within the [[source rock]], the volume of hydrocarbons produced from kerogen increases until a continuous mass forms (a slug) that has enough force to overcome the capillary forces of the largest pore throat network. At that time, the slug moves into the closest coarse-grained bed. Expulsion is preferentially upward because of the hydrocarbons' buoyancy, but it may be downward due to [[Petroleum generation|generation]] and compaction pressure if the pathway is less restrictive. Expulsion probably acts discontinuously, resulting in periodic slugs of migrating hydrocarbons. Broad compositional differences between the slug and those hydrocarbons generated from the kerogen appear to be due to preferential retention of large hydrocarbons by fine pores.

Slug flow (or bulk phase flow) is generally accepted as the dominant mechanism of primary hydrocarbon migration. Within the [[source rock]], the volume of hydrocarbons produced from kerogen increases until a continuous mass forms (a slug) that has enough force to overcome the capillary forces of the largest pore throat network. At that time, the slug moves into the closest coarse-grained bed. Expulsion is preferentially upward because of the hydrocarbons' buoyancy, but it may be downward due to [[Petroleum generation|generation]] and compaction pressure if the pathway is less restrictive. Expulsion probably acts discontinuously, resulting in periodic slugs of migrating hydrocarbons. Broad compositional differences between the slug and those hydrocarbons generated from the kerogen appear to be due to preferential retention of large hydrocarbons by fine pores.

==Slug flow in secondary, tertiary, and remigration==

==Slug flow in secondary, tertiary, and remigration==

==Pressure effects==

==Pressure effects==

At pressures that exceed the critical point for hydrocarbon mixtures, the terms “gas phase” and “oil phase” become ambiguous. A single phase generally occurs at pressures above 4,000 psi and temperatures above [[temperature::200°F]] ([[temperature::93°C]]). For a hydrostatic gradient, this pressure converts to a little less than [[depth::9,000 ft]] with a geothermal gradient of about [[temperature::1.5°F]]/100 ft and a surface temperature of [[temperature::70°C]].

At pressures that exceed the critical point for hydrocarbon mixtures, the terms “gas phase” and “oil phase” become ambiguous. A single phase generally occurs at pressures above 4,000 psi and temperatures above [[temperature::200°F]] ([[temperature::93°C]]). For a hydrostatic gradient, this pressure converts to a little less than [[depth::9,000 ft]] with a geothermal gradient of about [[temperature::1.5°F]]/100 ft and a surface temperature of [[temperature::70°C]].

==Phase effects on composition==

==Phase effects on composition==

==Compositional changes during phase changes==

==Compositional changes during phase changes==

[[file:migration-of-petroleum_fig7-7.png|300px|thumb|{{figure number|2}}Composition of each phase and the mass partitioning of the migrating-gas phase as the liquids are trapped. After Lingerer et al. (1984).{{citation needed}}]]

[[file:migration-of-petroleum_fig7-7.png|300px|thumb|{{figure number|2}}Composition of each phase and the mass partitioning of the migrating-gas phase as the liquids are trapped. After Ungerer et al.<ref name=Ungerer1984>Ungerer, P., F. Behar, P. Y. Chenet, B. Durand, E. Nogaret, A. Chiarelli, J. L. Oudin, and J. F. Perrin, 1984, [http://archives.datapages.com/data/specpubs/geochem1/data/a028/a028/0001/0050/0053.htm Geological and Geochemical models in oil exploration, principles and practical examples], in G. Demaison and R .J. Murris, eds., Petroleum Geochemistry and Basin Evaluation: AAPG Memoir no. 35, p. 53–77.</ref>]]

Phase migration occurs when a gas is expelled with oil or migrates through an oil-rich source rock. The figure below shows the gasoline range and heavier hydrocarbons in a single-phase fluid expelled from a source rock at 3000 m. As the fluid migrates upward to lower temperatures and pressures, it undergoes a process called separation migration. At 2500 m, the 100 tons of single phase have separated into 40 tons of gas and 60 tons of oil.

Phase migration occurs when a gas is expelled with oil or migrates through an oil-rich source rock. The figure below shows the gasoline range and heavier hydrocarbons in a single-phase fluid expelled from a source rock at 3000 m. As the fluid migrates upward to lower temperatures and pressures, it undergoes a process called separation migration. At 2500 m, the 100 tons of single phase have separated into 40 tons of gas and 60 tons of oil.