Relating Seismic Data to Stratigraphy
Stratigraphic interpretation of seismic data requires that the seismic information be expressed in geological terms. The strictly geological view of the earth is developed from surface observations, guiding principles of geological evolution and subsurface Information from bore holes. Amongst the subsurface information are well log measurements from a variety of physical sensors. We can correlate the information content of the seismic data with the geologic view in terms of geometric description and a subset of the log measurements, namely velocity and density. Such correlation used in context with geological and geophysical principles is at the heart of stratigraphic interpretation.
Typically available well log measurements include the Spontaneous Potential, Resistivities, Radioactivity parameters, Sonic Travel Times (Velocity) and Densities. While the vertical detailing of such measurements is excellent, they are quite limited in the extent to which they define subsurface parameters laterally. Hence, a strong interpretive element enters the picture in which appeal is made to fundamental geological concepts and principles. Still, such measurements can provide insights about the porosity and fluid contents of the rocks and the lithology in general which enhance stratigraphic conclusions based solely on a geologic approach.
Seismic measurements on the other hand do define in some sense the subsurface geometry and give estimates of the acoustic impedance which is related to the rock velocities and densities. The vertical detail is rather limited owing to the size of the seismic wavelet and it's observation principally as sequences of overlapped events, but the lateral definition is quite good although