Difference between revisions of "Seismic data: building a stratigraphic model"
FWhitehurst (talk | contribs) (→VSPs) |
Cwhitehurst (talk | contribs) m (added Category:Treatise Handbook 3 using HotCat) |
||
(17 intermediate revisions by 2 users not shown) | |||
Line 6: | Line 6: | ||
| part = Predicting the occurrence of oil and gas traps | | part = Predicting the occurrence of oil and gas traps | ||
| chapter = Interpreting seismic data | | chapter = Interpreting seismic data | ||
− | | frompg = 12- | + | | frompg = 12-13 |
− | | topg = 12- | + | | topg = 12-14 |
| author = Christopher L. Liner | | author = Christopher L. Liner | ||
| link = http://archives.datapages.com/data/specpubs/beaumont/ch12/ch12.htm | | link = http://archives.datapages.com/data/specpubs/beaumont/ch12/ch12.htm | ||
Line 14: | Line 14: | ||
| isbn = 0-89181-602-X | | isbn = 0-89181-602-X | ||
}} | }} | ||
− | The problem addressed in seismic modeling, or simulation, is calculating the seismic response (traveltime and amplitude) for a given stratigraphic model. The stratigraphic model consists of those physical properties that influence seismic wave propagation—typically compressional wave speed, shear wave speed, and mass density. This set of parameters can describe the simplest possible solid, called an isotropic elastic solid. For some purposes, it is sufficient to consider the earth as an acoustic (fluid) medium characterized by only two parameters: sound speed (''υ'') and mass density (ρ). Seismic reflections are generated where there is a contrast in impedance (which is the product of velocity and density). | + | The problem addressed in seismic modeling, or simulation, is calculating the seismic response ([http://wiki.seg.org/wiki/Dictionary:Traveltime traveltime] and [http://wiki.seg.org/wiki/Dictionary:Amplitude amplitude]) for a given stratigraphic model. The stratigraphic model consists of those physical properties that influence seismic wave propagation—typically [http://wiki.seg.org/wiki/Dictionary:P-wave compressional wave] speed, [http://wiki.seg.org/wiki/Dictionary:S-wave shear wave] speed, and [http://physics.about.com/od/fluidmechanics/f/density.htm mass density]. This set of parameters can describe the simplest possible solid, called an [http://www.merriam-webster.com/dictionary/isotropic isotropic] [http://wiki.seg.org/wiki/Dictionary:Elastic_deformation elastic] solid. For some purposes, it is sufficient to consider the earth as an acoustic (fluid) medium characterized by only two parameters: sound speed (''υ'') and mass density (ρ). [http://wiki.seg.org/wiki/Dictionary:Reflection Seismic reflections] are generated where there is a contrast in impedance (which is the product of velocity and density). |
==Velocity data sources== | ==Velocity data sources== | ||
Line 20: | Line 20: | ||
* [http://wiki.seg.org/wiki/Dictionary:Vertical_seismic_profiling_%28VSP%29 Vertical seismic profile (VSP)] | * [http://wiki.seg.org/wiki/Dictionary:Vertical_seismic_profiling_%28VSP%29 Vertical seismic profile (VSP)] | ||
− | * Sonic | + | * [[Basic_open_hole_tools#Sonic|Sonic log]] with [[Checkshots_and_vertical_seismic_profiles#Checkshot_surveys|checkshots]] |
− | * Sonic | + | * Sonic log without checkshots |
* Checkshots only | * Checkshots only | ||
+ | |||
+ | See also [[Checkshots and vertical seismic profiles]]. | ||
==VSPs== | ==VSPs== | ||
Line 28: | Line 30: | ||
[[file:interpreting-seismic-data_fig12-6.png|thumb|300px|{{figure number|1}}Example of a zero-offset VSP. Copyright: Landmark Graphics.]] | [[file:interpreting-seismic-data_fig12-6.png|thumb|300px|{{figure number|1}}Example of a zero-offset VSP. Copyright: Landmark Graphics.]] | ||
− | A [http://wiki.seg.org/wiki/Dictionary:Vertical_seismic_profiling_%28VSP%29 vertical seismic profile (VSP)] yields the best connection between geologic horizons and seismic events. It is recorded by using a source at the surface and many receiver locations down a wellbore, or vice versa. The receivers record full traces for interpretation. The receiver spacing is usually [[length::10 ft]]. This gives actual traveltimes from the surface to points in the earth, and it is the best and most direct method of associating seismic events with geological horizons. The kind of VSP shown in [[:file:interpreting-seismic-data_fig12-6.png|Figure 1]] (produced by commercial software) is often called a zero-offset VSP, meaning that only a single source position is used as close to the wellhead as possible. It is relatively inexpensive. There are also multioffset and multiazimuth VSPs, which use many source locations. These are much more expensive and sometimes are useful for local, high-resolution imaging. However, a zero-offset VSP is sufficient for event identification and 3-D seismic calibration. | + | A [http://wiki.seg.org/wiki/Dictionary:Vertical_seismic_profiling_%28VSP%29 vertical seismic profile (VSP)] yields the best connection between geologic horizons and seismic events. It is recorded by using a source at the surface and many [http://wiki.seg.org/wiki/Dictionary:Receiver receiver] locations down a wellbore, or vice versa. The receivers record full [http://wiki.seg.org/wiki/Dictionary:Seismic_trace traces] for interpretation. The receiver spacing is usually [[length::10 ft]]. This gives actual [http://wiki.seg.org/wiki/Dictionary:Traveltime traveltimes] from the surface to points in the earth, and it is the best and most direct method of associating seismic events with geological horizons. The kind of VSP shown in [[:file:interpreting-seismic-data_fig12-6.png|Figure 1]] (produced by commercial software) is often called a zero-[[offset]] VSP, meaning that only a single source position is used as close to the wellhead as possible. It is relatively inexpensive. There are also multioffset and multiazimuth VSPs, which use many source locations. These are much more expensive and sometimes are useful for local, high-resolution imaging. However, a zero-offset VSP is sufficient for event identification and [[3-D seismic data: the data cube|3-D seismic data]] calibration. |
==Velocities from sonic logs== | ==Velocities from sonic logs== | ||
− | Velocities can be acquired from sonic logs with or without a checkshot survey. A checkshot survey is like a baby VSP. The receivers are sparsely located down the well, usually on key geologic boundaries. Also, the information recovered is limited to arrival time (a number), unlike the full trace a VSP gives. The checkshots help correct for any drift in a sonic log due to missing log intervals or hole problems. This makes the calculated traveltimes more reliable. One can obtain good velocity data from sonic logs without checkshots. However, if there are any hole integrity problems, significant errors can exist in the sonic data. If a sonic log is not available, very coarse velocity data can be obtained from a checkshot survey with only 5 or 6 traveltimes per well. | + | Velocities can be acquired from sonic logs with or without a [[Checkshots_and_vertical_seismic_profiles#Checkshot_surveys|checkshot survey]]. A checkshot survey is like a baby VSP. The [http://wiki.seg.org/wiki/Dictionary:Receiver receivers] are sparsely located down the well, usually on key geologic boundaries. Also, the information recovered is limited to [http://wiki.seg.org/wiki/Dictionary:Arrival_time arrival time] (a number), unlike the full [http://wiki.seg.org/wiki/Dictionary:Seismic_trace trace] a [[Checkshots_and_vertical_seismic_profiles#Vertical_seismic_profiles|VSP]] gives. The checkshots help correct for any drift in a [[Basic_open_hole_tools#Sonic|sonic log]] due to missing log intervals or [[Drilling problems|hole problems]]. This makes the calculated traveltimes more reliable. One can obtain good velocity data from sonic logs without checkshots. However, if there are any hole integrity problems, significant errors can exist in the sonic data. If a sonic log is not available, very coarse velocity data can be obtained from a checkshot survey with only 5 or 6 traveltimes per well. |
+ | |||
+ | ==Density data == | ||
+ | Density information can improve the accuracy of a stratigraphic model for seismic analysis. | ||
− | + | Velocity can be estimated from a [[density log]] if a sonic log is not available, but data from a sonic log is much better. | |
− | |||
==See also== | ==See also== | ||
+ | * [[Seismic data]] | ||
* [[Synthetic seismogram]] | * [[Synthetic seismogram]] | ||
* [[Synthetic seismograms: correlation to other data]] | * [[Synthetic seismograms: correlation to other data]] | ||
* [[Seismic data: identifying reflectors]] | * [[Seismic data: identifying reflectors]] | ||
+ | * [[Checkshots and vertical seismic profiles]] | ||
==External links== | ==External links== | ||
Line 48: | Line 54: | ||
[[Category:Predicting the occurrence of oil and gas traps]] | [[Category:Predicting the occurrence of oil and gas traps]] | ||
[[Category:Interpreting seismic data]] | [[Category:Interpreting seismic data]] | ||
+ | [[Category:Treatise Handbook 3]] |
Latest revision as of 19:06, 27 January 2022
Exploring for Oil and Gas Traps | |
Series | Treatise in Petroleum Geology |
---|---|
Part | Predicting the occurrence of oil and gas traps |
Chapter | Interpreting seismic data |
Author | Christopher L. Liner |
Link | Web page |
Store | AAPG Store |
The problem addressed in seismic modeling, or simulation, is calculating the seismic response (traveltime and amplitude) for a given stratigraphic model. The stratigraphic model consists of those physical properties that influence seismic wave propagation—typically compressional wave speed, shear wave speed, and mass density. This set of parameters can describe the simplest possible solid, called an isotropic elastic solid. For some purposes, it is sufficient to consider the earth as an acoustic (fluid) medium characterized by only two parameters: sound speed (υ) and mass density (ρ). Seismic reflections are generated where there is a contrast in impedance (which is the product of velocity and density).
Velocity data sources
Depth-dependent velocity and density models are needed to identify events or to create a synthetic seismogram. Velocity information can come from a variety of sources. Here is a list, in order of preference:
- Vertical seismic profile (VSP)
- Sonic log with checkshots
- Sonic log without checkshots
- Checkshots only
See also Checkshots and vertical seismic profiles.
VSPs
A vertical seismic profile (VSP) yields the best connection between geologic horizons and seismic events. It is recorded by using a source at the surface and many receiver locations down a wellbore, or vice versa. The receivers record full traces for interpretation. The receiver spacing is usually length::10 ft. This gives actual traveltimes from the surface to points in the earth, and it is the best and most direct method of associating seismic events with geological horizons. The kind of VSP shown in Figure 1 (produced by commercial software) is often called a zero-offset VSP, meaning that only a single source position is used as close to the wellhead as possible. It is relatively inexpensive. There are also multioffset and multiazimuth VSPs, which use many source locations. These are much more expensive and sometimes are useful for local, high-resolution imaging. However, a zero-offset VSP is sufficient for event identification and 3-D seismic data calibration.
Velocities from sonic logs
Velocities can be acquired from sonic logs with or without a checkshot survey. A checkshot survey is like a baby VSP. The receivers are sparsely located down the well, usually on key geologic boundaries. Also, the information recovered is limited to arrival time (a number), unlike the full trace a VSP gives. The checkshots help correct for any drift in a sonic log due to missing log intervals or hole problems. This makes the calculated traveltimes more reliable. One can obtain good velocity data from sonic logs without checkshots. However, if there are any hole integrity problems, significant errors can exist in the sonic data. If a sonic log is not available, very coarse velocity data can be obtained from a checkshot survey with only 5 or 6 traveltimes per well.
Density data
Density information can improve the accuracy of a stratigraphic model for seismic analysis.
Velocity can be estimated from a density log if a sonic log is not available, but data from a sonic log is much better.
See also
- Seismic data
- Synthetic seismogram
- Synthetic seismograms: correlation to other data
- Seismic data: identifying reflectors
- Checkshots and vertical seismic profiles