60th EAGE Conference and Exhibition

In [1] and [2], we introduced a. new tomographic method, Stereotomography, for estirnating velocity macro rnodels from seismic reflection data.

Migration velocity analysis (MVA) should allow interpreters to check and improve the complex velocity models required for 3D pre-stack depth imaging

The estimation of macromodels containing laterally varying velocities presents no problem for the method which is based on on the global inversion of focusing operators.

A crucial issue when processing seismic data is the ability to remove coherent noise while preserving the amplitudes of the signal. Strong noise (multiple reflections, ground roll, converted waves in compression mode analysis) interferes with the signal and can lead to incorrect pre stack attributes and to erroneous interpretations of the final images at target level.

The use in recent years of offset-to-reflector depth ratios of two or three rather than the unity common earlier has resulted in traveltime-offset curves that are not hyperbolic. For long offsets or where anisotropy is important, a need to include a quartic term in the squared traveltime-squared offset function has been established. Long offsets are common today for AVO analysis in areas such as the Gulf of Mexico.

The cross-spread is the basic subset of the orthogonal geometry. It is a single-fold 3D data set which was shown by Vermeer et al. (1995) to be suitable for DMO. This was good news, because DMO was usually regarded as an operation on common-offset common-azimuth (COA) subsets of the acquisition geometry.

Application of Wave Equation Datuming (WED) can produce dramatically improved seismic images. However the technique has not received the degree of acceptance it probably deserves for a number of reasons

Until quite recently, multicomponent recording has been a minor part of the seismic market, and systems have required expensive and time consuming adaptation to facilitate 4-C recording (three component velocity plus a pressure transducer). The cost and inconvenience of these adaptations has lead to a cost premium in 4-C. As the value of 4-C is becoming apparent, from numerous experimental surveys, it is now time to rethink some of the basic system design concepts to address the practicalities of efficient 4-C recording.

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