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Unformatted text preview: ors in borehole consists of: • Signals arrive from above the tool: which is direct arrival & downgoing multiples • Signals arrive from below the tool: which is direct reflections & upgoing multiples There are many types of VSP survey: • Zero-offset VSP: n which the energy source is positioned directly above the receivers, typically very close to the wellbore. • Offset VSP: in which the source is located at an offset from the drilling rig during acquisition. This allows imaging to Walk‐above some distance away from the wellbore. Walk‐away • Movable source VSP: in this case the source is not stationary. • Walk-away VSP: in which the source is moved to progressively farther offset at the surface and receivers are held in a fixed location, effectively providing a mini 2D seismic line that can be of higher resolution than surface seismic data and provides more continuous coverage than an offset VSP • Walk-in VSP: originating from successive shots fired from far offset source with decreasing offset. • Walk-above VSP: accommodate the geometry of a deviated well; sometimes called a vertical incidence VSP. Each receiver is in a different lateral position with the source directly above the receiver for all cases. Such data provide a high-resolution seismic image of the subsurface below the trajectory of the well. Zero‐offset Offset VSP Synthetic Seismogram: It is a result of one of many forms of forward modeling to predict the seismic response of the Earth. A more narrow definition used by seismic interpreters is that a synthetic seismogram, commonly called a synthetic. it is a direct one-dimensional model of acoustic energy traveling through the layers of the Earth. The synthetic seismogram is generated by convolving the reflectivity derived from digitized acoustic and density logs with the wavelet derived from seismic data. By comparing marker beds or other correlation points picked on well logs with major reflections on the seismic section, interpretations of the data can be improved. The quality of the match between a synth...
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This note was uploaded on 01/05/2011 for the course GEOL 1 taught by Professor Jenniferalford during the Spring '10 term at Indian Institute of Technology, Roorkee.
- Spring '10