Changes

The interpretation process can be subdivided into three interrelated categories: structural, stratigraphic, and lithologic. Structural seismic interpretation is directed toward the creation of structural maps of the subsurface from the observed three-dimensional configuration of arrival times. Seismic sequence stratigraphic interpretation relates the pattern of reflections observed to a model of cyclic episodes of deposition. The aim is to develop a chronostratigraphic framework of cyclic, genetically related strata. Lithologie interpretation is aimed at determining changes in pore fluid, [[porosity]], fracture intensity, lithology, and so on from seismic data. Direct hydrocarbon indicators (DHI, HCIs, bright spots, or dim-outs) are elements employed in this lithologic interpretation process.

The interpretation process can be subdivided into three interrelated categories: structural, stratigraphic, and lithologic. Structural seismic interpretation is directed toward the creation of structural maps of the subsurface from the observed three-dimensional configuration of arrival times. Seismic sequence stratigraphic interpretation relates the pattern of reflections observed to a model of cyclic episodes of deposition. The aim is to develop a chronostratigraphic framework of cyclic, genetically related strata. Lithologie interpretation is aimed at determining changes in pore fluid, [[porosity]], fracture intensity, lithology, and so on from seismic data. Direct hydrocarbon indicators (DHI, HCIs, bright spots, or dim-outs) are elements employed in this lithologic interpretation process.

This chapter discusses a basic three-step methodology, which when followed provides for a more complete and accurate geological interpretation from seismic data.

This article discusses a basic three-step methodology, which, when followed, provides for a more complete and accurate geological interpretation from seismic data.

==Step one: interpretation plan==

==Step one: interpretation plan==

===What seismic patterns should I be looking for?===

===What seismic patterns should I be looking for?===

Perhaps the most common interpretational pitfall, and certainly one of the most dangerous, is the mapping of events, amplitude, or AVO changes without qualification as to what geological analog they represent. To prevent this mistake, it is critical that all types of available geological data be gathered and merged with the seismic data. Key to this merging are well-constructed [[synthetic seismograms]], vertical seismic profiling (VSP) data, and/or seismic models (see “[[Synthetic seismograms]],” “Checkshots and Vertical Seismic Profiles,” and “Forward Modeling of Seismic Data”). This verifies the seismic signature of the target, the location of the mapping horizon, and the adequacy of the time-depth functions. Varying the synthetic seismogram or model parameters allows for the prediction of seismic responses for various lithologics and fluid types.

Perhaps the most common interpretational pitfall, and certainly one of the most dangerous, is the mapping of events, amplitude, or AVO changes without qualification as to what geological analog they represent. To prevent this mistake, it is critical that all types of available geological data be gathered and merged with the seismic data. Key to this merging are well-constructed [[synthetic seismograms]], vertical seismic profiling (VSP) data, and/or seismic models (see [[Synthetic seismograms]], [[Checkshots and vertical seismic profiles]], and [[Forward modeling of seismic data]]). This verifies the seismic signature of the target, the location of the mapping horizon, and the adequacy of the time-depth functions. Varying the synthetic seismogram or model parameters allows for the prediction of seismic responses for various lithologics and fluid types.

==Step two: building and merging datasets==

==Step two: building and merging datasets==

Available well, core, test, [[paleontology]], and outcrop data are gathered and organized for integration with the seismic data. Where available, gravity and [[magnetics]] data should be tied to the seismic data to identify the location of basement, salt bodies, igneous intrusives, and shale masses. Another type of data that sheds light on the geological conditions of a specific reservoir is pressure and production history data. These data can provide information on the presence and proximity of faulting and the size of fault blocks.

Available well, core, test, [[paleontology]], and outcrop data are gathered and organized for integration with the seismic data. Where available, gravity and [[magnetics]] data should be tied to the seismic data to identify the location of basement, salt bodies, igneous intrusives, and shale masses. Another type of data that sheds light on the geological conditions of a specific reservoir is pressure and production history data. These data can provide information on the presence and proximity of faulting and the size of fault blocks.

If digital data are available, a decision must be made whether to use a workstation or proceed with a “paper interpretation.” Generally, a workstation offers the interpreter a valuable edge achieving a “correct” interpretation where detail is important (see the chapter in “Two-Dimensional Geophysical Workstation Interpretation: Generic Problems”). For much regional work, paper is often still the most used medium due to the display limitations of the workstation screen. Seismic interpretations on paper, however, can always be digitized later for computer mapping or incorporation into a workstation project.

If digital data are available, a decision must be made whether to use a workstation or proceed with a “paper interpretation.” Generally, a workstation offers the interpreter a valuable edge achieving a “correct” interpretation where detail is important (see [[Two-dimensional geophysical workstation interpretation: generic problems and solutions]]). For much regional work, paper is often still the most used medium due to the display limitations of the workstation screen. Seismic interpretations on paper, however, can always be digitized later for computer mapping or incorporation into a workstation project.

==Step three: interpretation==

==Step three: interpretation==

* Seismic velocity maps for lithology determination or depth conversion

* Seismic velocity maps for lithology determination or depth conversion

In addition, many combinations of these maps can be made, such as seismic amplitude plotted on top of structure. The only limitations in constructing these maps are the imagination and skill of the interpreter (see “Mapping”).

In addition, many combinations of these maps can be made, such as seismic amplitude plotted on top of structure. The only limitations in constructing these maps are the imagination and skill of the interpreter (see [[Mapping with two-dimensional seismic data]]).

The overall aim of seismic interpretation is to aid in constructing the most accurate earth model or reservoir description possible. This can best be accomplished when the seismic data are merged with petrophysical, geological, and engineering databases. While the process of interpreting seismic data is basically the same on paper or in a workstation environment, the workstation offers advantages in data management, manipulation, and display and it allows for a more convenient integration of other data types.

The overall aim of seismic interpretation is to aid in constructing the most accurate earth model or reservoir description possible. This can best be accomplished when the seismic data are merged with petrophysical, geological, and engineering databases. While the process of interpreting seismic data is basically the same on paper or in a workstation environment, the workstation offers advantages in data management, manipulation, and display and it allows for a more convenient integration of other data types.