Seismic Sequence Analysis
Exercise One

HOW TO TIE SYNTHETIC FROM WELLS TO THE SEISMIC LINES THEY PENETRATE

As explained in the introduction to the web site, sequence stratigraphy is used to subdivide the sedimentary section into geometric packages bounded unconformities and internal surfaces, and infer the relationship of these geometries to changes in base level (sea level and tectonic movement) and rates of sedimentation.

These inferences and sequence stratigraphic analyses are often based on seismic cross-sections, well logs and outcrop studies of sedimentary rocks and are used to predict the continuity and extent of their lithology. Usually seismic provides the regional control on the geometries of sequences and wells are used to determine the lithology of these geometries. To achieve this latter a tie must be made between local wells and local seismic.

Thus the purpose of the exercise below is to introduce the common method for tying the local stratigraphy of a region to seismic cross-sections that dissect it.

HOW A SYNTHETIC SEISMIC TRACE IS GENERATED

Your task is to take a well (the Zablotny #1) drilled in the Little Knife Oil Field in the Williston Basin and tie this to a North South seismic line across this field. To achieve the latter a synthetic seismic trace had be generated for the Zablotny #1.

3) A zero phase, normal polarity Ricker wavelet, was convolved with the reflection coefficients to produce the synthetic seismic trace beside the two way travel time log model for the Zablonty #1.

4) Finally the geophysicists, consulting with geologists, established the vertical position of the stratigraphic tops penetrated by the Zablotny #1.

THE EXERCISE

The seismic line used in this exercise was provided by the Gulf Oil Company and was interpreted in the two publications by Lindsay, and Kendall l985, and Rafavich, Kendall, & Todd l984.

To gain access to the un-interpreted seismic section click on the image to left to download it or print it (click here for a smaller version of same section). Print the file of the seismic and the well log and follow the procedures outlined below.

 

To gain access to the Synthetic trace image, click on the images to left to download it or print it.

 

For the exercise use colored pencils to mark the location of the tops of the Green Horn Formation, Piper Lime Formation, Spearfish Formation, Amsden Formation, Base of Last Salt, Mission Canyon Formation, Duperow Formation, Red River Formation, Winnepeg Formation, Deadwood Formation and Basement on the synthetic.
Now fold the synthetic trace at the seismic trace and overlay this on the seismic line at the location of the Zablotny #1 well. Mark the various tops on the seismic, correlate and color these so they can be traced across the seismic line. List the formation names of the tops where they intersect the edges of the seismic line.

The final step in the exercise should be to write up a short analysis describing the steps you have taken and the conclusions you made based on your interpretation of the seismic line and the regional geology.

SOLUTION

To gain access to the interpreted seismic section and match it with your interpretation click on the image to left to download it or print it (click here for a smaller version of same section).

 

RELEVANT LINKS

For more information on impedance, reflection coefficients and synthetic seismic review the Schumberger Oil Field Glossary) and Acoustic Impedance.

Kansas Geological Survey, Open File Report 96-50 provides more details on synthetics and tying of wells to seismic data.

University of Southern Ontario provides good introduction to Synthetics and Seismic Interpretaion.

The Ocean Drilling Program (ODP) provides excellent section on Seismic Stratigraphy and Synthetics.

The Geophysical Corner of AAPG EXPLORER has a good section on various geophysical concepts. (this is an example link to principles of VSP).

ESIinfo basic geophysical terminology.

West Virginia University Fault/Horizon Interpretation Using Kingdom Suite (SMT).

Geogia Tech Seismic Resources on the World Wide Web

Seismic wave theory in the US: 1991--1994: Jeffrey Park from Yale University/Department of Geology and Geophysics provides a good review of seismic wave theory complete with references.

CREWES (The Consortium For Research in Elastic Wave Exploration Seismology) provides excellent bried introduction of wave conversion with outstanding graphics for clarifying concepts.

UCSC - Relating Boreholes or Outcrops to Seismic Data: Synthetic Seismograms and Other Tools. This is an excellent introduction to creating synthetics with many images illustrating the various tools and obtained images.

University of Lausanne page that deals with Teaching seismic interpretation provides introduction to reflection seismology and 3D seismic survey concepts.

Colorado School of Mines Reservoir Characterization Project/Chapter on Surface Seismic Calibration deals with how synthetic seismograms are created and how they can be utilized for seismic interpretation.

Kansas Geological Survey section on Seismic records and the synthetic seismogram provides clear steps needed to compute synthetic seismograms using sonic logs.

REFERENCES

l985 Lindsay, R.F., and C.G.St.C.Kendall, Depositional facies, diagenesis, and reservoir character of Mississippian cyclic carbonates in the Mission Canyon Formation, Little Knife Field, Williston Basin, North Dakota: in P.O. Roehl and P.W. Choquette eds. Carbonate petroleum reservoirs: Springer Verlag New York, p. l75-l90.

l984 Rafavich, F., C.G.St.C.Kendall, and T.P. Todd, The relationship between acoustic properties and the petrographic character of carbonate rocks: Geophysics, v. 49, p. l622-l636