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7th Middle East Geosciences Conference and Exhibition
Manama, Bahrain
March 27-29, 2006
Migration
and Model Building
Geophysics Department - Stanford Exploration Project, Stanford University, Mitchell Bldg, 397 Panama Mall,
Stanford, CA 94305-2215, phone: (650)723-1319, [email protected]
Large hydrocarbon reservoirs are located below salt bodies in several areas of the world, such as the Gulf of Mexico, the Persian Gulf, and offshore West Africa. In these areas, economical recovery of the hydrocarbons depends on our ability to image the reservoir with seismic data. Seismic imaging below salt bodies is a challenging task that pushes the limits of current imaging methods. The difficulties are associated with the complexity of the wave -propagation phenomena that occur when the seismic wavefield interacts with the salt body (e.g. multi -pathing, scattering, mode conversion) and with the structural complexity of the salt bodies and the target reservoirs.
The routine use of 3-D prestack depth migration
, and in particular of wave-equation
migration
, had a positive impact on
many exploration projects. However, simple
migration
has difficulties to produce artifact-free images where the salt
geometry prevents an even illumination of the subsalt reflectors from surface data.
A promising research direction is to go beyond simple wave-equation migration
and instead iteratively invert 3-D waveequation
operators. I will illustrate this idea by describing two research projects. The first project aims at improving the
image of poorly illuminated areas by inverting a 3-D one-way wavefield operator. The second project developed a robust
Migration
Velocity Analysis (MVA) method based on wave-equation operator, that can be used where conventional raybased
tomography fails. This method bypasses the difficulties involved in tracing high-frequency rays through a complex
salt body and accurately models finite-frequency wave propagation.