Imaging below a complex overburden with borehole-seismic data

Abstract

We have determined how the measured polarization and traveltime for P- and S-waves can be used directly with vertical seismic profile data for estimating the salt exit points in a salt-proximity survey. As with interferometry, the processes described use only local velocities. For the data analyzed in this paper, our procedures have confirmed the location, inferred from surface-seismic data, of the flank of a steeply dipping salt body near the well. This has provided us more confidence in the estimated reservoir extent moving toward the salt face, which in turn has added critical information for the economic evaluation of a possible new well into the reservoir. We also have found that ray-based vector migration, based on the assumptions of locally plane wavefronts and locally plane formation interfaces, can be used to create 3D reflection images of steeply dipping sediments near the well, again using only local velocities. Our local reflection images have helped confirm the dips of the sediments between the well and the salt flank. Because all parameters used in these processes are local and can be extracted from the data themselves, the processes can be considered to be self-sufficient.

Imaging complex three‐dimensional structures, applying three‐component vector migration to synthetic vertical seismic profiling data

“…This process was developed further by Haldorsen et al . (2015) and Haldorsen and Jahren (2020). The next paragraphs summarize this work, for simplicity of arguments – replacing the general Green's propagators by a time‐delay or a time‐advance operator.…”

“…We then summarize the ray‐based vector migration process for three‐component data, based on Haldorsen (2002), Haldorsen et al . (2013, 2015), and Haldorsen and Jahren (2020), as pertaining to general imaging with Vertical Seismic Profiling data, using semblance‐weighted deconvolution in the imaging condition. This ray‐based formulation, including explicit use of particle‐motion polarization to establish whether a specific component of the wavefield could possibly originate – or be reflected, converted or refracted – at a specific point in the three‐dimensional volume is under investigation.…”

“…The work described in this present paper partially predates and did support the work reported by Haldorsen et al . (2013, 2015), Haldorsen and Jahren (2019, 2020), but was not cleared for publication until recently. Their work demonstrates that vector migration when applied to field data create reasonably looking images.…”

“…With the present data set, we can demonstrate that the vector migration process allows the reconstruction of both steeply dipping salt flanks, and the sediments that have been dragged along by the moving salt and truncated against the sides of the salt body. Haldorsen and Jahren (2020) explore the use of vector migration to image exit points from salt sediment interfaces. Although the migration smiles essentially are the remains of not‐properly‐cancelled isochron surfaces, the wavefield projections used in the formulation promoted by Haldorsen (2002) (and used in the work reported on here) limit the active part of the isochron surface by a cosine tapering.…”

“…Extending an idea by Kiyashchenko et al . (2009), Haldorsen and Jahren (2020) suggest using ‘fat rays’ with aperture. This may be a decent compromise, but has not been used for the analyses in this article.…”