In chapter 3 I showed that for a synthetic crosswell experiment PS transmission arrivals may be migrated to locate a vertical boundary parallel to the boreholes, a boundary that is invisible to PP reflections. It was also demonstrated that the reduced-time imaging condition introduced in chapter 2 could be applied to these data to decrease the focusing errors due to an incorrect migration velocity. Wavepath migration was applied to the crosswell data to reduce the migration artifacts by limiting the migration to the Fresnel zone at the specular transmission point.
Utilizing the synthetic RVSP data I applied PS and SP transmission migration as well as PP reflection migration to locate the vertical boundary. Due to the velocities chosen SP transmission migration was able to image approximately two-thirds of the boundary, PP reflection migration one-half of the boundary, and PS transmission migration one-third of the boundary. As for the crosswell simulation, the reduced-time imaging condition migrated the energy more accurately than conventional migration for an incorrect velocity model. To account for errors in the migration velocity model, wavepath migration should smear migrated energy along several Fresnel zones.
A salt diapir model was used to test the feasibility of migrating PS transmission events for a more complex model. Although PS transmission migration of the entire shot gather delineated the diapir flanks, migrating only the PS transmission events illuminates the diapir flank more clearly.
In chapter 4, PS transmission migration of the Kidd Creek crosswell data and the Gulf of Mexico VSP data demonstrated the feasibility of imaging the transmitting boundaries. The use of reduced-time migration with the Kidd Creek data clearly showed better focusing and more accurate imaging than images obtained with conventional migration. Applying reduced-time migration to the Kidd Creek data illustrated that in the presence of an unknown time shift transmitted SP arrivals and reflected PP arrivals can be used to accurately image the transmitting and reflecting boundaries. For these data, the base of the ore body would have remained unimaged without the availability of PS transmitted arrivals.
The Gulf of Mexico VSP data were successfully migrated to reconstruct the top and bottom of the tabular salt body even though the top of the salt body was above the receiver array. This further illustrates the utility of migrating transmitted PS arrivals to illuminate boundaries invisible to PP reflections.
In summary, migration of transmitted converted waves and reduced-time migration are two new tools that can be used to reduce imaging error and illuminate nearly vertical boundaries, or "dark" parts of salt flanks, ore bodies, and other targets.
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