Inversion of walkaway VSP data in the presence of lateral velocity heterogeneity
Multi-azimuth walkaway vertical seismic profiling is an established technique for the estimation of in situ slowness surfaces and inferring anisotropy parameters. Normally, this technique requires the assumption of lateral homogeneity, which makes the horizontal slowness components at depths of down...
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| Format: | Article |
| Language: | English |
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KeAi Communications Co., Ltd.
2024-04-01
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| Series: | Energy Geoscience |
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| Online Access: | http://www.sciencedirect.com/science/article/pii/S2666759223001014 |
| _version_ | 1797200788156579840 |
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| author | Vladimir Grechka Ilya Tsvankin Pedro Contreras |
| author_facet | Vladimir Grechka Ilya Tsvankin Pedro Contreras |
| author_sort | Vladimir Grechka |
| collection | DOAJ |
| description | Multi-azimuth walkaway vertical seismic profiling is an established technique for the estimation of in situ slowness surfaces and inferring anisotropy parameters. Normally, this technique requires the assumption of lateral homogeneity, which makes the horizontal slowness components at depths of downhole receivers equal to those measured at the surface. Any violations of this assumption, such as lateral heterogeneity or nonzero dip of intermediate interfaces, lead to distortions in reconstructed slowness surfaces and, consequently, to errors in estimated anisotropic parameters. In this work, we relax the assumption of lateral homogeneity and discuss how to correct vertical seismic profile data for weak lateral heterogeneity. We describe a procedure of downward continuation of recorded traveltimes that accounts for the presence of both vertical inhomogeneity and weak lateral heterogeneity, which produces correct slowness surfaces at depths of downhole receivers, noticing that sufficiently dense receiver coverage along a borehole is required to separate influences of vertical and lateral heterogeneity on measured traveltimes and obtain accurate estimates of the slowness surfaces. Once the slowness surfaces are found and a desired type of anisotropic model to be inverted is selected, the corresponding anisotropic parameters, providing the best fit to the estimated slownesses, can be obtained. We invert the slowness surfaces of P-waves for parameters of the simplest anisotropic model describing dipping fractures (transversely isotropic medium with a tilted symmetry axis). Five parameters of this model, namely, the P-wave velocity V0 in the direction of the symmetry axis, Thomsen's anisotropic coefficients ϵ and δ, the tilt ν, and the azimuth β of the symmetry axis, can be estimated in a stable manner when maximum source offset is greater than half of receiver depth. |
| first_indexed | 2024-04-24T07:37:13Z |
| format | Article |
| id | doaj.art-3fd96befb33142ba9645cec1c310531f |
| institution | Directory Open Access Journal |
| issn | 2666-7592 |
| language | English |
| last_indexed | 2024-04-24T07:37:13Z |
| publishDate | 2024-04-01 |
| publisher | KeAi Communications Co., Ltd. |
| record_format | Article |
| series | Energy Geoscience |
| spelling | doaj.art-3fd96befb33142ba9645cec1c310531f2024-04-20T04:17:55ZengKeAi Communications Co., Ltd.Energy Geoscience2666-75922024-04-0152100255Inversion of walkaway VSP data in the presence of lateral velocity heterogeneityVladimir Grechka0Ilya Tsvankin1Pedro Contreras2CWP, Department of Geophysics, Colorado School of Mines, Golden, CO, 80401, USA; Borehole Seismic LLC, USACWP, Department of Geophysics, Colorado School of Mines, Golden, CO, 80401, USAPDVSA-INTEVEP, Apartado 76343, Caracas, 1070A, Venezuela; Department of Physics, ULA, Venezuela; Corresponding author. Department of Physics, ULA, Venezuela.Multi-azimuth walkaway vertical seismic profiling is an established technique for the estimation of in situ slowness surfaces and inferring anisotropy parameters. Normally, this technique requires the assumption of lateral homogeneity, which makes the horizontal slowness components at depths of downhole receivers equal to those measured at the surface. Any violations of this assumption, such as lateral heterogeneity or nonzero dip of intermediate interfaces, lead to distortions in reconstructed slowness surfaces and, consequently, to errors in estimated anisotropic parameters. In this work, we relax the assumption of lateral homogeneity and discuss how to correct vertical seismic profile data for weak lateral heterogeneity. We describe a procedure of downward continuation of recorded traveltimes that accounts for the presence of both vertical inhomogeneity and weak lateral heterogeneity, which produces correct slowness surfaces at depths of downhole receivers, noticing that sufficiently dense receiver coverage along a borehole is required to separate influences of vertical and lateral heterogeneity on measured traveltimes and obtain accurate estimates of the slowness surfaces. Once the slowness surfaces are found and a desired type of anisotropic model to be inverted is selected, the corresponding anisotropic parameters, providing the best fit to the estimated slownesses, can be obtained. We invert the slowness surfaces of P-waves for parameters of the simplest anisotropic model describing dipping fractures (transversely isotropic medium with a tilted symmetry axis). Five parameters of this model, namely, the P-wave velocity V0 in the direction of the symmetry axis, Thomsen's anisotropic coefficients ϵ and δ, the tilt ν, and the azimuth β of the symmetry axis, can be estimated in a stable manner when maximum source offset is greater than half of receiver depth.http://www.sciencedirect.com/science/article/pii/S2666759223001014Walkaway vertical seismic profileLateral velocity heterogeneityAnisotropic parameter estimationVertical inhomogeneity |
| spellingShingle | Vladimir Grechka Ilya Tsvankin Pedro Contreras Inversion of walkaway VSP data in the presence of lateral velocity heterogeneity Energy Geoscience Walkaway vertical seismic profile Lateral velocity heterogeneity Anisotropic parameter estimation Vertical inhomogeneity |
| title | Inversion of walkaway VSP data in the presence of lateral velocity heterogeneity |
| title_full | Inversion of walkaway VSP data in the presence of lateral velocity heterogeneity |
| title_fullStr | Inversion of walkaway VSP data in the presence of lateral velocity heterogeneity |
| title_full_unstemmed | Inversion of walkaway VSP data in the presence of lateral velocity heterogeneity |
| title_short | Inversion of walkaway VSP data in the presence of lateral velocity heterogeneity |
| title_sort | inversion of walkaway vsp data in the presence of lateral velocity heterogeneity |
| topic | Walkaway vertical seismic profile Lateral velocity heterogeneity Anisotropic parameter estimation Vertical inhomogeneity |
| url | http://www.sciencedirect.com/science/article/pii/S2666759223001014 |
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