Difference between revisions of "Hydrocarbon migration"
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| − | '''Migration''' of | + | '''Migration''' of [[hydrocarbon]]s is a little-understood but critical process of the [[petroleum system]]. The short definition is: Movement of petroleum from source rock toward a reservoir or seep. [[Primary migration]] is expulsion of petroleum from fine-grained source rock, while [[secondary migration]] moves petroleum through a coarse-grained carrier bed or fault to a reservoir or seep. [[Tertiary migration]] occurs when petroleum moves from one trap to another or to a seep.<ref name=Petersetal_2012>Peters, Kenneth E., David J. Curry, and Marek Kacewicz, 2012, [http://archives.datapages.com/data/specpubs/hedberg4/INTRODUCTION/INTRODUCTION.HTM An overview of basin and petroleum system modeling: Definitions and concepts], ''in'' Peters, Kenneth E., David J. Curry, and Marek Kacewicz, eds., Basin modeling: New horizons in research and applications: [http://store.aapg.org/detail.aspx?id=1106 AAPG Hedberg Series no. 4], p. 1-16.</ref> |
| + | |||
| + | The following questions are vital for understanding the complications of the process: | ||
* How does oil escape from the [[source rock]]? | * How does oil escape from the [[source rock]]? | ||
* Does oil migrate out of the [[trap]]? | * Does oil migrate out of the [[trap]]? | ||
| − | * Why are there marked differences in [[ | + | * Why are there marked differences in [[API gravity|oil gravity]], wax content, and sulfur content in [[lateral]] and stratigraphically successive sands? |
* Why are there differences in water salinity for multiple sands in one [[structural trap system|structural trap]]? | * Why are there differences in water salinity for multiple sands in one [[structural trap system|structural trap]]? | ||
* What is the role of [[fault]]s in transporting and trapping hydrocarbons? | * What is the role of [[fault]]s in transporting and trapping hydrocarbons? | ||
| Line 12: | Line 14: | ||
==Principles of migration== | ==Principles of migration== | ||
| − | * | + | * [[Hydrocarbon]]s migrate as a separate phase, primarily due to [[Buoyancy forces in reservoir fluids|buoyancy]]. This force causes them to move vertically at geologically rapid rates. |
* Lithologic layers slow or restrict the vertical movement of hydrocarbons. [[Seal]]s deflect the hydrocarbons laterally up [[dip]] through underlying beds to a [[trap]] or spill point. Lateral migration is also facilitated by meteoric groundwater flow. Flow rates for compaction-driven water generally are too slow to significantly affect hydrocarbon flow. | * Lithologic layers slow or restrict the vertical movement of hydrocarbons. [[Seal]]s deflect the hydrocarbons laterally up [[dip]] through underlying beds to a [[trap]] or spill point. Lateral migration is also facilitated by meteoric groundwater flow. Flow rates for compaction-driven water generally are too slow to significantly affect hydrocarbon flow. | ||
* The properties of [[reservoir]]s and carrier beds (dip, [[relative permeability]], etc.) control the rate of migration and thus the specific direction of the bulk of hydrocarbons under seals. | * The properties of [[reservoir]]s and carrier beds (dip, [[relative permeability]], etc.) control the rate of migration and thus the specific direction of the bulk of hydrocarbons under seals. | ||
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==Observations of migration== | ==Observations of migration== | ||
| − | Hydrocarbon migration has been observed only rarely and indirectly in the natural environment under atypical conditions. Observation is difficult because it occurs either too rapidly, too slowly, or elsewhere. As such, migration is generally inferred rather than demonstrated. Conclusions about migration are based on snapshots in reservoir and source-rock systems. Laboratory migration experiments are limited in their applications by the time frame and the ability to reproduce subsurface conditions. | + | [[Hydrocarbon]] migration has been observed only rarely and indirectly in the natural environment under atypical conditions. Observation is difficult because it occurs either too rapidly, too slowly, or elsewhere. As such, migration is generally inferred rather than demonstrated. Conclusions about migration are based on snapshots in reservoir and source-rock systems. Laboratory migration experiments are limited in their applications by the time frame and the ability to reproduce subsurface conditions. |
==Migration studies== | ==Migration studies== | ||
| − | The movement of | + | The movement of [[hydrocarbon]]s through an entire stratigraphic section is generally ignored. Geochemists usually focus on migration out of [[source rock]]s, and [[Subsurface team|reservoir engineers]] usually study migration within carrier beds ([[reservoir]]-quality rocks). Little is known, though much is inferred, about cross-facies flow required when source rocks and reservoir-quality rocks are not adjacent to one another. |
==Migration constraints== | ==Migration constraints== | ||
| − | Physical conditions constraining migration through stratigraphic sections are [[Wikipedia:Pressure|pressure]], [[Wikipedia:Temperature|temperature]], [[permeability]], [[Capillary pressure|capillarity]], [http://hyperphysics.phy-astr.gsu.edu/hbase/surten.html surface tension], molecular size, and [http://physics.about.com/od/fluidmechanics/f/density.htm density]. The main chemical constraint is [[Wikipedia:Solubility|solubility]] of migrating | + | Physical conditions constraining migration through stratigraphic sections are [[Wikipedia:Pressure|pressure]], [[Wikipedia:Temperature|temperature]], [[permeability]], [[Capillary pressure|capillarity]], [http://hyperphysics.phy-astr.gsu.edu/hbase/surten.html surface tension], molecular size, and [http://physics.about.com/od/fluidmechanics/f/density.htm density]. The main chemical constraint is [[Wikipedia:Solubility|solubility]] of migrating [[hydrocarbon]]s. |
==Chemistry of migrated hydrocarbons== | ==Chemistry of migrated hydrocarbons== | ||
| − | Detailed chemical correlations made of | + | Detailed chemical correlations made of [[reservoir]]ed [[hydrocarbon]]s with source rocks strongly indicate that the migration process does not significantly affect the overall [[geochemistry]] of the migrated hydrocarbons. However, general differences exist between the chemical composition of oils and the source rocks to which they are chemically correlated. These differences must be explained. |
==How we observe migration== | ==How we observe migration== | ||
| − | Materials trapped in diagenetic overgrowths offer snapshots of the migration process. Studies of these materials by microanalytical techniques such as fluid inclusion analysis, microfluorescence, and cathodoluminescence offer potential for great advances in our understanding of the migration process and our ability to recognize and perhaps predict migration pathways and timing. | + | Materials trapped in [http://bio-geo-terms.blogspot.com/2006/10/overgrowth.html diagenetic overgrowths] offer snapshots of the migration process. Studies of these materials by microanalytical techniques such as [http://www.geotrack.com.au/fluidinclusion.htm fluid inclusion] analysis, microfluorescence, and [[SEM,_XRD,_CL,_and_XF_methods#Cathodoluminescence_.28CL.29|cathodoluminescence]] offer potential for great advances in our understanding of the migration process and our ability to recognize and perhaps predict migration pathways and timing. |
==Migration stages== | ==Migration stages== | ||
Hydrocarbon migration consists of four stages: primary, secondary, tertiary, and remigration. The list below contains their definitions. | Hydrocarbon migration consists of four stages: primary, secondary, tertiary, and remigration. The list below contains their definitions. | ||
| − | * '''Primary Migration'''—The process of loss of | + | * '''Primary Migration'''—The process of loss of [[hydrocarbon]]s from the [[source rock]]. |
| − | * '''Secondary Migration'''—Migration from source to reservoir along a simple or complex carrier system. Includes migration within the reservoir rock itself. | + | * '''Secondary Migration'''—Migration from source to [[reservoir]] along a simple or complex carrier system. Includes migration within the reservoir rock itself. |
* '''Tertiary Migration'''—Migration to the surface, either from a reservoir or source rock. Also called dismigration. | * '''Tertiary Migration'''—Migration to the surface, either from a reservoir or source rock. Also called dismigration. | ||
* '''Remigration'''—Migration from one reservoir position through an intervening section into another reservoir position in the same or a different reservoir. | * '''Remigration'''—Migration from one reservoir position through an intervening section into another reservoir position in the same or a different reservoir. | ||
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* [[Migration by solution in water]] | * [[Migration by solution in water]] | ||
* [[Migration by separate phase]] | * [[Migration by separate phase]] | ||
| + | |||
| + | ==References== | ||
| + | {{reflist}} | ||
[[Category:Critical elements of the petroleum system]][[Category:Migration of petroleum]] | [[Category:Critical elements of the petroleum system]][[Category:Migration of petroleum]] | ||
Latest revision as of 14:33, 6 April 2016
Migration of hydrocarbons is a little-understood but critical process of the petroleum system. The short definition is: Movement of petroleum from source rock toward a reservoir or seep. Primary migration is expulsion of petroleum from fine-grained source rock, while secondary migration moves petroleum through a coarse-grained carrier bed or fault to a reservoir or seep. Tertiary migration occurs when petroleum moves from one trap to another or to a seep.[1]
The following questions are vital for understanding the complications of the process:
- How does oil escape from the source rock?
- Does oil migrate out of the trap?
- Why are there marked differences in oil gravity, wax content, and sulfur content in lateral and stratigraphically successive sands?
- Why are there differences in water salinity for multiple sands in one structural trap?
- What is the role of faults in transporting and trapping hydrocarbons?
- Why are there barren sands within sequences of productive sands?
- How is cross-formational flow of hydrocarbons accomplished?
- Does the form change during migration and, if so, which form is dominant under what conditions?
- How can we estimate the timing, volumes, and compositions of transported hydrocarbons?
Principles of migration
- Hydrocarbons migrate as a separate phase, primarily due to buoyancy. This force causes them to move vertically at geologically rapid rates.
- Lithologic layers slow or restrict the vertical movement of hydrocarbons. Seals deflect the hydrocarbons laterally up dip through underlying beds to a trap or spill point. Lateral migration is also facilitated by meteoric groundwater flow. Flow rates for compaction-driven water generally are too slow to significantly affect hydrocarbon flow.
- The properties of reservoirs and carrier beds (dip, relative permeability, etc.) control the rate of migration and thus the specific direction of the bulk of hydrocarbons under seals.
Less is known about migration than any other process involved in the accumulation of hydrocarbons in the subsurface. It is generally described as that unknown process or group of processes that enable petroleum to move from a source to a reservoir.
Observations of migration
Hydrocarbon migration has been observed only rarely and indirectly in the natural environment under atypical conditions. Observation is difficult because it occurs either too rapidly, too slowly, or elsewhere. As such, migration is generally inferred rather than demonstrated. Conclusions about migration are based on snapshots in reservoir and source-rock systems. Laboratory migration experiments are limited in their applications by the time frame and the ability to reproduce subsurface conditions.
Migration studies
The movement of hydrocarbons through an entire stratigraphic section is generally ignored. Geochemists usually focus on migration out of source rocks, and reservoir engineers usually study migration within carrier beds (reservoir-quality rocks). Little is known, though much is inferred, about cross-facies flow required when source rocks and reservoir-quality rocks are not adjacent to one another.
Migration constraints
Physical conditions constraining migration through stratigraphic sections are pressure, temperature, permeability, capillarity, surface tension, molecular size, and density. The main chemical constraint is solubility of migrating hydrocarbons.
Chemistry of migrated hydrocarbons
Detailed chemical correlations made of reservoired hydrocarbons with source rocks strongly indicate that the migration process does not significantly affect the overall geochemistry of the migrated hydrocarbons. However, general differences exist between the chemical composition of oils and the source rocks to which they are chemically correlated. These differences must be explained.
How we observe migration
Materials trapped in diagenetic overgrowths offer snapshots of the migration process. Studies of these materials by microanalytical techniques such as fluid inclusion analysis, microfluorescence, and cathodoluminescence offer potential for great advances in our understanding of the migration process and our ability to recognize and perhaps predict migration pathways and timing.
Migration stages
Hydrocarbon migration consists of four stages: primary, secondary, tertiary, and remigration. The list below contains their definitions.
- Primary Migration—The process of loss of hydrocarbons from the source rock.
- Secondary Migration—Migration from source to reservoir along a simple or complex carrier system. Includes migration within the reservoir rock itself.
- Tertiary Migration—Migration to the surface, either from a reservoir or source rock. Also called dismigration.
- Remigration—Migration from one reservoir position through an intervening section into another reservoir position in the same or a different reservoir.
See also
- Factors that cause migration
- Factors that oppose hydrocarbon migration
- Migration pathways
- Calculating migration rate
- Calculating charge volume
- Estimating expulsion efficiency
- Migration by solution in water
- Migration by separate phase
References
- ↑ Peters, Kenneth E., David J. Curry, and Marek Kacewicz, 2012, An overview of basin and petroleum system modeling: Definitions and concepts, in Peters, Kenneth E., David J. Curry, and Marek Kacewicz, eds., Basin modeling: New horizons in research and applications: AAPG Hedberg Series no. 4, p. 1-16.