The Converted-P (or SV-P) Mode: Valuable and Already in Your Possession but Not Utilized
by Bob A. Hardage
BIO
Bob A. Hardage received a PhD in physics from Oklahoma State University. His thesis work focused on high-velocity micro-meteoroid impact on space vehicles, which required trips to Goddard Space Flight Center to do finite-difference modeling on dedicated computers. Upon completing his university studies, he worked at Phillips Petroleum Company for 23 years and was Exploration Manager for Asia and Latin America when he left Phillips. He moved to WesternAtlas and worked 3 years as Vice President of Geophysical Development and Marketing. He then established a multicomponent seismic research laboratory at the Bureau of Economic Geology and served The University of Texas at Austin as a Senior Research Scientist for 28 years. He has published books on VSP, cross-well profiling, seismic stratigraphy, and multicomponent seismic technology. He was the first person to serve 6 years on the Board of Directors of the Society of Exploration Geophysicists (SEG). His Board service was as SEG Editor (2 years), followed by 1-year terms as First VP, President Elect, President, and Past President. SEG has awarded him a Special Commendation, Life Membership, and Honorary Membership. He wrote the AAPG Explorer column on geophysics for 6 years. AAPG honored him with a Distinguished Service award for promoting geophysics among the geological community.
Abstract
Common P-wave sources (vertical vibrators, buried explosives, vertical impacts) generate down-going S-wavefields that are suitable for S-mode imaging. The basic physics of this long-ignored principle will be explained, and then S-wave illumination by P sources will be demonstrated with numerical modeling, field tests, and several real-data images.
The down-going SV illuminating wavefield produced by a P source creates up-going P and SV reflections at deep interfaces. Up-going SV-SV reflections are recorded by horizontal geophones, and up-going SV-P reflections are recorded by vertical geophones. We will focus on SV-P data because 1000s of sq. mi. of unused SV-P data already exist, which means SV-P imaging can be done at many locations for zero data-acquisition cost.
The 200-year-old Reciprocity Principle will be applied to show that SV-P vertical-geophone data are identical to P-SV horizontal-geophone data, the latter being an imaging option that has been used for 30 years. The Reciprocity Principle implies that any advantage that has been provided by horizontal-geophone P-SV data during the past 3 decades can also be provided by vertical-geophone SV-P data. The truth of this reciprocity claim will be demonstrated by comparing real-data P-SV and SV-P images.
Probably the most important applications of P-SV data have been achieved by segregating reflected P-SV wavefields into fast-S and slow-S images. I will show that SV-P reflection wavefields can also be segregated into fast-S and slow-S wavefields. Specifically fast-S and slow-S azimuths will be determined in all 98,000 stacking bins that comprise a 24 sq. mi. vertical-geophone survey that was used to evaluate a site for CO2 sequestration. This P-source, vertical-geophone survey was acquired 8 years before this SV-P fast-S/slow-S analysis was done.
