Bob A. Hardage

Lecture BH1: Expanding Seismic Stratigraphy to the Full-Elastic Wavefield

The principles of seismic stratigraphy form the foundation of seismic data interpretation and establish a methodology by which depositional environments, stratigraphic relationships, reservoir architecture, and distributions of rock types can be inferred from seismic sequences and seismic facies.  The science of seismic stratigraphy was introduced in a formalized manner in the 1970’s using P-wave seismic data, and thousands of geological problems have been analyzed with seismic stratigraphy concepts since the 1970’s using only P-wave seismic data.

Even though the principles of seismic stratigraphy can be applied to S-wave seismic data in the same way that the concepts are applied to P-wave data, only a few examples of seismic stratigraphy studies in which S-wave data are analyzed can be found in the literature.  Scientists at the Bureau of Economic Geology have found that interpreting the full-elastic wavefield with seismic stratigraphy principles yields more geological information than when a seismic stratigraphy interpretation is limited to only the P-wave mode of the elastic wavefield.  This discussion will summarize some of these research findings and will present examples where elastic-wavefield seismic stratigraphy provides geological information that cannot be provided by single-component P-wave seismic stratigraphy.

Lecture BH2: Deepwater Hydrates in the Gulf of Mexico

Hydrates are found in shallow, near-seafloor sediments in most deep-water environments. The source of the hydrocarbon gases that form these hydrates can be biogenic or thermogenic in origin. In prolific hydrocarbon basins such as the Gulf of Mexico, thermogenic gases can make a significant contribution to deepwater hydrate systems, particularly when there are vertical permeability pathways for deep gases to migrate upward to the seafloor where pressure and temperature conditions are optimal for hydrate stability.
Scientists at the Bureau of Economic Geology have developed unique methods for studying deepwater hydrates across the Gulf of Mexico. In these studies, 4-component ocean-bottom-cable (4C OBC) seismic data are used to produce high-resolution P-P and P-SV images of near-seafloor geology. Although the energy source used to generate the 4C OBC data is a standard air gun array towed at a depth of a few meters and which generates an illuminating wavefield with frequencies less than 200 Hz, geological detail as small as one meter can be imaged using proper data-processing procedures.

This discussion will explain how hydrate is embedded in near-seafloor sediment, illustrate the nature of the hydrate targets that are to be imaged, show how high-resolution target imaging is achieved, describe how P-wave and S-wave seismic attributes are used to estimate hydrate concentration, and compare seismic estimates of hydrate concentration with estimates calculated from resistivity logs at calibration wells.

Hardage, B. A., 2000, Vertical seismic profiling: principles: third updated and revised edition: New York, Pergamon, Seismic Exploration, v. 14, 552 p.

Hardage, B. A., 2007, Fundamentals of geophysics, in Holstein, E. D., ed., Volume V(A), Reservoir engineering and petrophysics, in Lake, L. W., ed.-in-chief, Petroleum engineering handbook: Society of Petroleum Engineers, p. V-25–V-75.

Hardage, B. A., Carr, D. L., Lancaster, D. E., Simmons, J. L., Jr., Elphick, R. Y., Pendleton, V. M., and Johns, R. A., 1996, 3-D seismic evidence of the effects of carbonate karst collapse on overlying clastic stratigraphy and reservoir compartmentalization: Geophysics, v. 61, no. 5, p. 1336–1350.