### Abstract

Original language | English |
---|---|

Pages (from-to) | S69-S79 |

Journal | Geophysics |

Volume | 78 |

Issue number | 2 |

DOIs | |

Publication status | Published - 2013 |

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*Geophysics*, vol. 78, no. 2, pp. S69-S79. https://doi.org/10.1190/GEO2012-0182.1

**Time-lapse wave-equation migration velocity analysis.** / Shragge, Jeffrey; Lumley, David.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Time-lapse wave-equation migration velocity analysis

AU - Shragge, Jeffrey

AU - Lumley, David

PY - 2013

Y1 - 2013

N2 - Time-lapse (4D) analysis of seismic data acquired at different stages of hydrocarbon production or gas/fluid injection has been very successful at imaging detailed reservoir changes. Conventional time-domain analysis of 4D data sets usually assumes a linear perturbation about a reference baseline earth model. However, this assumption is violated when production/injection significantly alters the subsurface generating large 4D velocity changes, time shifts, and complicated 4D wavefield coda, necessitating a more robust 4D analysis involving prestack wave-equation depth migration and velocity analysis. We address these situations by extending conventional 3D waveequation migration velocity analysis (WEMVA) based on one-way wave-equations and single-scattering theory to 4D velocity estimation using a "parallel" inversion approach involving parallel solution of two separate inversion problems. Recognizing that the 4D WEMVA strategy requires precomputed baseline/monitor image-difference volumes, we develop an approximate 4D WEMVA technique that replaces these differences with a single weight function derived from the smooth background time-lapse image difference. We demonstrate the usefulness of the parallel and an approximate 4D WEMVA approach using a synthetic time-lapse CO2 geosequestration experiment that requires inverting for a thin-layer velocity change derived from CO2 injection in an analogue North Sea reservoir. The parallel 4DWEMVA solutions generate an excellent highresolution velocity estimates, whereas the approximate methods recover lower-resolution estimates with magnitudes thatmust be rescaled through a post-inversion gradient line-search © 2013 Society of Exploration Geophysicists.

AB - Time-lapse (4D) analysis of seismic data acquired at different stages of hydrocarbon production or gas/fluid injection has been very successful at imaging detailed reservoir changes. Conventional time-domain analysis of 4D data sets usually assumes a linear perturbation about a reference baseline earth model. However, this assumption is violated when production/injection significantly alters the subsurface generating large 4D velocity changes, time shifts, and complicated 4D wavefield coda, necessitating a more robust 4D analysis involving prestack wave-equation depth migration and velocity analysis. We address these situations by extending conventional 3D waveequation migration velocity analysis (WEMVA) based on one-way wave-equations and single-scattering theory to 4D velocity estimation using a "parallel" inversion approach involving parallel solution of two separate inversion problems. Recognizing that the 4D WEMVA strategy requires precomputed baseline/monitor image-difference volumes, we develop an approximate 4D WEMVA technique that replaces these differences with a single weight function derived from the smooth background time-lapse image difference. We demonstrate the usefulness of the parallel and an approximate 4D WEMVA approach using a synthetic time-lapse CO2 geosequestration experiment that requires inverting for a thin-layer velocity change derived from CO2 injection in an analogue North Sea reservoir. The parallel 4DWEMVA solutions generate an excellent highresolution velocity estimates, whereas the approximate methods recover lower-resolution estimates with magnitudes thatmust be rescaled through a post-inversion gradient line-search © 2013 Society of Exploration Geophysicists.

U2 - 10.1190/GEO2012-0182.1

DO - 10.1190/GEO2012-0182.1

M3 - Article

VL - 78

SP - S69-S79

JO - Geophysics

JF - Geophysics

SN - 0016-8033

IS - 2

ER -