- Hello, my name is Kelly Bergman and today, I'm going to discuss an introduction to seismic stratigraphy. This is the first in a series of lectures on seismic stratigraphy. Seismic stratigraphy is the interpretation of geologic information and stratigraphic relationships from seismic reflection data. It's a method that allows scientists to apply stratigraphic concepts, the same concepts used to interpret rock, core and well logs to reflection pattern data obtained from the subsurface. The patterns are used to interpret lithology, stratigraphic architecture and depositional environment, and to correlate depositional surfaces and stratigraphic packages. It also allows for the correlation of stratigraphy over long distances and in between wells. By tying the seismic to well information such as well logs, the interpreter can extend geologic information, such as stratigraphic ages, lithology and reservoir information into inter-well regions. Seismic stratigraphy was first developed as an interpretation technique in a series of papers by Peter Vail and colleagues in 1977. The authors recognized that seismic reflections are generated by bedded sedimentary rocks. The same types of stratigraphic patterns and concepts observed on the surface could be recognized and then interpreted in seismic data. To understand how stratigraphic concepts can be applied to seismic reflection data, it is important to know the origin of seismic reflections. A reflection is produced when the seismic signal encounters an acoustic impedance contrast in the subsurface. Impedance is a product of rock density and velocity. Bedded sedimentary rocks exhibit a strong impedance contrast so lend themselves to be well-imaged by seismic reflection data. In most cases, these contrasts occur at stratigraphic surfaces in unconformities, and those are chronostratigraphic or time-equivalent surfaces. The seismic section on the left is located along the slope platform transition of Great Bahama Bay. The labeled horizons are sequence boundaries, or unconformities that are chronostratigraphic surfaces and have been verified by biostratigraphic age dating. Facies boundaries do not usually produce sufficient impedance contrast to produce a significant reflection, but it is possible. The seismic section on the right is from a field in the Permian Basin. The depositional facies interpretation shows the transition from an inner shelf to slope environment. Transition across the shelf crest creates a sufficient contrast in impedance due to lithology changes that a reflection is created that is not chronostratigraphic, but lithostratigraphic. Seismic stratigraphy is an incredibly useful tool that has wide applications in exploration and development. General types of geologic information that can be gained from seismic stratigraphy includes lithology, identification of depositional units and distribution, stratigraphic and depositional history, geologic time correlations, paleogeography, geologic history, burial history and paleo-surface mapping, including many more types of information. In hydrocarbon exploration, seismic stratigraphy allows for the identification and interpretation of plays, correlation of information from areas of data to areas of no or little data, development of prospects, mapping of reservoir and seal, and appraisal well planning. In development and production, seismic stratigraphy is used to identify map reservoir facies. It allows the prediction of the occurrence and extent of reservoir and non-reservoir and to plan walls accordingly. At the top of this slide is a workflow that illustrates the general steps in seismic interpretation. In general, before beginning the detailed analysis, data is prepared that will aid in the interpretation process such as identifying key lines with well ties and plotting base maps. Then, general information on the regional setting is established to orient the interpreter. This may include identifying the structural style of the region and the broad depositional settings such as shelf margin or basinal setting. At this point, ages may be correlated into the data as well. The geologic framework interpretation step includes both a structural component and a stratigraphic component. The workflow at the bottom of the slide shows the three main steps of stratigraphic interpretation. Seismic sequence analysis is the identification and correlation of lapouts, unconformities and stratigraphic packages. Seismic facies analysis is the identification and interpretation of seismic facies based on seismic character and seismic facies mapping. Data integration is the use of additional information such as biostratigraphy, well logs, lithologic information and paleogeography to aid in the interpretation. In summary, seismic stratigraphy is the interpretation of geologic information and stratigraphic relationships from seismic reflection data. It allows for the application of stratigraphic concepts to the subsurface. The pattern data is used to interpret lithology, depositional environment and depositional sequences. Seismic reflections are chronostratigraphic in nature but in some cases can be lithostratigraphic boundaries. Seismic stratigraphy has important applications and is widely used in hydrocarbon exploration and development. The important steps in seismic stratigraphy include seismic sequence analysis, seismic facies analysis and data integration. Seismic sequence analysis and seismic facies analysis will be further discussed in additional lectures. Thank you for your time.