Overpressuring at the base of salt is a serious drilling hazard in subsalt exploration. Even thin salt sills can be highly efficient fluid seals. As a result, we sometimes encounter extremely overpressured sediments immediately under salt. This paper suggests we may be able to predict overpressuring at base of salt by comparing primary and converted mode seismic reflection amplitudes.

We now recognize that base of salt primary and converted mode reflection amplitudes are often of similar strength (e.g., Kessinger et al., 1998 and Kessinger and Ramaswamy, 1996). Given that we already know the lithology on one side of the base of salt boundary, the presence of strong P-wave and C-wave reflections may present an ideal opportunity for recognizing lithology, fluid content and pressure conditions immediately beneath this boundary.

This work was part of Monica's Rice University master's thesis. Monica finished her graduate work in spring 1999 and is now working in Houston for Kerr-McGee.

Other work on the seismic response of salt

"Subsalt imaging using mode converted energy and acoustic depth migration," Walter Kessinger and Murali Ramaswamy, presented at the Fall 1996 International SEG Meeting in Denver. This abstract has a nice demonstration of imaging the base of salt with converted mode reflections using prestack depth migration.

"Elastic modeling initiative, part II: converted mode energy in subsalt exploration," Walter Kessinger, Monica Miley, Manik Talwani and Robert Wiley. Our 1998 project report to Lawrence Livermore National Laboratory. This paper has some beautiful examples of base of salt mode conversions from the Ewing Bank area. The figures were taken from Monica Miley's thesis work.

"Elastic wavefield modeling of salt bodies," Walter Kessinger and Riju John, presented at the Fall 1996 International SEG Meeting in Denver and at Subsalt '97 Subsalt Technology Conference and Exhibition, January 28-30 in Houston.

"Subsalt response of elastic wavefield modeling," Walter Kessinger, Ronit Strahilevitz and Murali Ramaswamy, presented at the Fall 1995 International SEG Meeting in Houston and the November 1995 GSH Processing SIG meeting.