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Forward numerical modeling of seismic data is the use of geological models of the earth to simulate seismic field experiments. Models can be one, two, or three dimensional and consist of depth horizons and associated P wave velocities, S wave velocities, and densities

Forward numerical modeling of [[seismic data]] is the use of geological models of the earth to simulate seismic field experiments. Models can be one, two, or three dimensional and consist of depth horizons and associated P wave velocities, S wave velocities, and densities

The most common use of forward modeling is for verification of structural and stratigraphic interpretations. For example, synthetic seismic sections derived from forward modeling can be compared to stacked sections to verify the original interpretation. If needed, the original interpretation or model is altered and the process repeated until a desired correlation between the actual data and modeled results is observed (see [[Synthetic seismograms]]).

The most common use of forward modeling is for verification of structural and stratigraphic interpretations. For example, synthetic seismic sections derived from forward modeling can be compared to stacked sections to verify the original interpretation. If needed, the original interpretation or model is altered and the process repeated until a desired correlation between the actual data and modeled results is observed (see [[Synthetic seismograms]]).

An example of the use of modeling to aid in stratigraphic interpretation is the use of amplitudes of seismic data to infer the thickness of a thin sand layer. If layer thickness is less than a wavelength, variations and thickness appear as tuning effects, with systematic changes in amplitude and wave shape correlating directly with sand thickness. Producing forward models with varying sand thickness using well data to calibrate, and comparing these synthetics with observed seismic sections, provides a means of accurately determining sand thickness where well data are sparse or absent.

An example of the use of modeling to aid in stratigraphic interpretation is the use of amplitudes of seismic data to infer the thickness of a thin sand layer. If layer thickness is less than a wavelength, variations and thickness appear as tuning effects, with systematic changes in amplitude and wave shape correlating directly with sand thickness. Producing forward models with varying sand thickness using well data to calibrate, and comparing these synthetics with observed seismic sections, provides a means of accurately determining sand thickness where well data are sparse or absent.

Another use of forward modeling is the determination of the seismic expression of expected features of the geology. [[:file:forward-modeling-of-seismic-data_fig1.png|Figures 1]] and [[:file:forward-modeling-of-seismic-data_fig2.png|2]] illustrate the use of seismic modeling to determine if [[porosity]] in a carbonate reef interval is detectable on seismic data. [[:file:forward-modeling-of-seismic-data_fig1.png|Figure 1]] is a [[strike]] [[cross section]] through a 3-D geological model representing a carbonate reef play. Reef structures are located in the interval between the depths of 2500 and [[depth::3500 ft]]. The structure located on the left side of the cross section contains porosity, while the structure on the right is tight. [[Porosity]] is represented in the model by a lower interval velocity and lower density than the surrounding rock (see [[Porosity]]).

Another use of forward modeling is the determination of the seismic expression of expected features of the geology. [[:file:forward-modeling-of-seismic-data_fig1.png|Figures 1]] and [[:file:forward-modeling-of-seismic-data_fig2.png|2]] illustrate the use of seismic modeling to determine if [[porosity]] in a carbonate [[reef]] interval is detectable on seismic data. [[:file:forward-modeling-of-seismic-data_fig1.png|Figure 1]] is a [[strike]] [[cross section]] through a 3-D geological model representing a carbonate reef play. Reef structures are located in the interval between the depths of 2500 and [[depth::3500 ft]]. The structure located on the left side of the cross section contains porosity, while the structure on the right is tight. [[Porosity]] is represented in the model by a lower interval velocity and lower density than the surrounding rock (see [[Porosity]]).

This study included the generation of two synthetic seismic sections using 3-D ray tracing techniques. One section represents a synthetic stacked seismic section (created using normal incidence ray tracing), while the second represents a synthetic migrated section (created using image ray tracing). The objective of modeling is to determine if there is a noticeable difference between the seismic signature of the tight carbonate and that of the porous carbonate. The synthetic migrated section is illustrated in [[:file:forward-modeling-of-seismic-data_fig2.png|Figure 2]]. The positive event at traces 20 through 26 and between 325 and 375 msec represents the top of the tight anticlinal structure. There is a distinct character change of this seismic event corresponding to a change in porosity in the geological model. The porosity is identified by the dim spot on traces 6 through 11 and the velocity pulldown of the underlying event. The results from this modeling indicate that seismic data could be used to identify porosity in this geological setting. A good description of modeling methods and a number of case study examples can be found in Fagin.<ref name=pt07r12>Fagin, S. W., 1991, Seismic Modeling of Geologic Structure: Tulsa, OK, Society of Exploration Geophysicists, Geophysical Development Series, v. 2.</ref>

This study included the generation of two synthetic seismic sections using 3-D ray tracing techniques. One section represents a synthetic stacked seismic section (created using normal incidence ray tracing), while the second represents a synthetic migrated section (created using image ray tracing). The objective of modeling is to determine if there is a noticeable difference between the seismic signature of the tight carbonate and that of the porous carbonate. The synthetic migrated section is illustrated in [[:file:forward-modeling-of-seismic-data_fig2.png|Figure 2]]. The positive event at traces 20 through 26 and between 325 and 375 msec represents the top of the tight anticlinal structure. There is a distinct character change of this seismic event corresponding to a change in porosity in the geological model. The porosity is identified by the dim spot on traces 6 through 11 and the velocity pulldown of the underlying event. The results from this modeling indicate that seismic data could be used to identify porosity in this geological setting. A good description of modeling methods and a number of case study examples can be found in Fagin.<ref name=pt07r12>Fagin, S. W., 1991, Seismic Modeling of Geologic Structure: Tulsa, OK, Society of Exploration Geophysicists, Geophysical Development Series, v. 2.</ref>

==Methods of forward modeling==

==Methods of forward modeling==

[[file:forward-modeling-of-seismic-data_fig1.png|thumb|300px|{{figure number|1}}A strike cross section of a carbonate reef play. The reef structure on the left contains porosity, while the reef structure on the right is tight.]]

[[file:forward-modeling-of-seismic-data_fig1.png|thumb|300px|{{figure number|1}}A strike cross section of a carbonate reef play. The [[reef]] structure on the left contains porosity, while the reef structure on the right is tight.]]

[[file:forward-modeling-of-seismic-data_fig2.png|thumb|300px|{{figure number|2}}[[Synthetic seismograms]] for the model in Figure 1. By synthetic modeling of a migrated section, the expected seismic signatures of reefs containing porosity and tight reefs have been obtained.]]

[[file:forward-modeling-of-seismic-data_fig2.png|thumb|300px|{{figure number|2}}[[Synthetic seismograms]] for the model in Figure 1. By synthetic modeling of a migrated section, the expected seismic signatures of reefs containing porosity and tight reefs have been obtained.]]

[[Category:Geophysical methods]]

[[Category:Geophysical methods]]