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| [[file:Geological_time_spiral.png|thumb|400px|The geologic time spiral.<ref name=USGS_2008>United States Geological Survey, 2008, Joseph Graham, William Newman, and John Stacy, [http://pubs.usgs.gov/gip/2008/58/ The geologic time spiral—A path to the past] (ver. 1.1): U.S. Geological Survey General Information Product 58.</ref>]] | | [[file:Geological_time_spiral.png|thumb|400px|The geologic time spiral.<ref name=USGS_2008>United States Geological Survey, 2008, Joseph Graham, William Newman, and John Stacy, [http://pubs.usgs.gov/gip/2008/58/ The geologic time spiral—A path to the past] (ver. 1.1): U.S. Geological Survey General Information Product 58.</ref>]] |
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− | Petroleum [[reservoir]]s may contain any of the three fluid phases—water (brine), oil, or gas. The initial distribution of phases depends on depth, [[Wikipedia:Temperature|temperature]], [[Wikipedia:Pressure|pressure]], composition, [[migration|historical migration]], type of geological [[trap]], and [[Geological heterogeneities|reservoir heterogeneity]] (that is, varying rock properties). The forces that originally distribute the fluids are [[gravity]], [[Capillary pressure|capillary]], [[molecular diffusion]], [[thermal convection]], and pressure gradients. It is generally assumed that reservoir fluids are in a static state when discovered or, more correctly, that fluids are moving at a very slow rate relative to the time required to extract the fluids (10 to 50 years). Clearly the fluids may still be in a dynamic state in terms of [[:file:Geological_time_spiral.png|geological time]]. | + | [[Petroleum]] [[reservoir]]s may contain any of the three fluid phases—water (brine), oil, or gas. The initial distribution of phases depends on depth, [[Wikipedia:Temperature|temperature]], [[Wikipedia:Pressure|pressure]], composition, [[migration|historical migration]], type of geological [[trap]], and [[Geological heterogeneities|reservoir heterogeneity]] (that is, varying rock properties). The forces that originally distribute the fluids are [[gravity]], [[Capillary pressure|capillary]], [[molecular diffusion]], [[thermal convection]], and pressure gradients. It is generally assumed that reservoir fluids are in a static state when discovered or, more correctly, that fluids are moving at a very slow rate relative to the time required to extract the fluids (10 to 50 years). Clearly the fluids may still be in a dynamic state in terms of [[:file:Geological_time_spiral.png|geological time]]. |
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| Because gravity is the dominant force in distributing fluids through geological time, [[hydrocarbon]]s migrate upward and are trapped against impermeable [http://www.oxforddictionaries.com/us/definition/american_english/cap-rock cap rock]. Gas overlies oil, which overlies water. However, because the reservoir pores are usually saturated completely by water before hydrocarbon [[migration]] and because capillary forces acting to retain water in the smallest pores exceed gravity forces, an initial ([[connate]]) [[water saturation]] will always be found in hydrocarbon-bearing formations. The connate water saturation may vary from 5 to 50% with the hydrocarbons still having sufficient mobility to produce at economical rates. | | Because gravity is the dominant force in distributing fluids through geological time, [[hydrocarbon]]s migrate upward and are trapped against impermeable [http://www.oxforddictionaries.com/us/definition/american_english/cap-rock cap rock]. Gas overlies oil, which overlies water. However, because the reservoir pores are usually saturated completely by water before hydrocarbon [[migration]] and because capillary forces acting to retain water in the smallest pores exceed gravity forces, an initial ([[connate]]) [[water saturation]] will always be found in hydrocarbon-bearing formations. The connate water saturation may vary from 5 to 50% with the hydrocarbons still having sufficient mobility to produce at economical rates. |
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| ===Composition or feed=== | | ===Composition or feed=== |
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− | Quantifies the amount of each component in a reservoir mixture, usually reported in mole fraction. Typical components in petroleum reservoir mixtures include the nonhydrocarbons N<sub>2</sub>, CO<sub>2</sub>, and H<sub>2</sub>S and the hydrocarbons C<sub>1</sub> C<sub>2</sub>, C<sub>3</sub> ''i''C<sub>4</sub> ''n''C<sub>4</sub>, ''i''C<sub>5</sub>, ''n''C<sub>5</sub>, C<sub>6</sub>, and C<sub>7+</sub> (C<sub>7+</sub>, or “heptanes-plus,” includes many hundreds of heavier compounds, such as paraffins, napthenes, and aromatics). Asphaltenes are also found in reservoir oils. | + | Quantifies the amount of each component in a reservoir mixture, usually reported in mole fraction. Typical components in petroleum reservoir mixtures include the nonhydrocarbons N<sub>2</sub>, CO<sub>2</sub>, and H<sub>2</sub>S and the hydrocarbons C<sub>1</sub> C<sub>2</sub>, C<sub>3</sub> ''i''C<sub>4</sub> ''n''C<sub>4</sub>, ''i''C<sub>5</sub>, ''n''C<sub>5</sub>, C<sub>6</sub>, and C<sub>7+</sub> (C<sub>7+</sub>, or “heptanes-plus,” includes many hundreds of heavier compounds, such as paraffins, napthenes, and aromatics). [[Asphaltenes]] are also found in reservoir oils. |
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| ===Saturated condition=== | | ===Saturated condition=== |
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| The water found in petroleum reservoirs is usually a ''brine'' consisting mostly of sodium chloride (NaCl) in quantities from 10 to 350 ppt (‰); seawater has about 35 ppt. Other compounds (electrolytes) found in reservoir brines include calcium (Ca), magnesium (Mg), sulfate (SO<sub>4</sub>), bicarbonate (HCO<sub>3</sub>), iodide (I), and bromide (Br). Brine specific gravity increases with salinity in units of about 0.075 per 100 ppt. | | The water found in petroleum reservoirs is usually a ''brine'' consisting mostly of sodium chloride (NaCl) in quantities from 10 to 350 ppt (‰); seawater has about 35 ppt. Other compounds (electrolytes) found in reservoir brines include calcium (Ca), magnesium (Mg), sulfate (SO<sub>4</sub>), bicarbonate (HCO<sub>3</sub>), iodide (I), and bromide (Br). Brine specific gravity increases with salinity in units of about 0.075 per 100 ppt. |
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− | At reservoir conditions, the brine that is sharing pore space with hydrocarbons always contains a limited amount of [[solution gas]] (mainly methane), from about 10 SCF/STB at 1000 psia to about 35 SCF/STB at 10,000 psia for gas-water systems and slightly less for oil-water systems. Increasing salinity decreases gas in solution. [http://water.usgs.gov/edu/compressibility.html Water compressibility] ranges from 2.5 to 5 × 10<sup>–6</sup> psi<sup>–1</sup>, decreasing with increasing salinity. Water [[Wikipedia:Viscosity|viscosity]] ranges from about 0.3 cP at high temperatures (>[[temperature::250°F]]) to about 1 cP at ambient temperatures, increasing with increasing salinity. Finally, reservoir brines exhibit only slight shrinkage (<5%) when produced to the surface. | + | At reservoir conditions, the brine that is sharing pore space with hydrocarbons always contains a limited amount of [[solution gas]] (mainly methane), from about 10 SCF/STB at 1000 psia to about 35 SCF/STB at 10,000 psia for gas-water systems and slightly less for oil-water systems. Increasing salinity decreases gas in solution. [http://water.usgs.gov/edu/compressibility.html Water compressibility] ranges from 2.5 to 5 × 10<sup>–6</sup> psi<sup>–1</sup>, decreasing with increasing salinity. Water [[viscosity]] ranges from about 0.3 cP at high temperatures (>[[temperature::250°F]]) to about 1 cP at ambient temperatures, increasing with increasing salinity. Finally, reservoir brines exhibit only slight shrinkage (<5%) when produced to the surface. |
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| ==Petroleum reservoir classifications== | | ==Petroleum reservoir classifications== |
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| * [[Conducting a reservoir simulation study: an overview]] | | * [[Conducting a reservoir simulation study: an overview]] |
| * [[Introduction to reservoir engineering methods]] | | * [[Introduction to reservoir engineering methods]] |
| + | * [[Reservoir fluids]] |
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| ==References== | | ==References== |
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| [[Category:Reservoir engineering methods]] | | [[Category:Reservoir engineering methods]] |
| + | [[Category:Methods in Exploration 10]] |