Changes

Cross-borehole tomography can be thought of as an extension of sonic logging to the reservoir cross section between two boreholes. The information obtained from cross-borehole tomography, when properly interpreted in the context of all available information, can often be invaluable for preparing accurate [[geological cross sections]] for reservoir development and planning.

Cross-borehole tomography can be thought of as an extension of sonic logging to the reservoir cross section between two boreholes. The information obtained from cross-borehole tomography, when properly interpreted in the context of all available information, can often be invaluable for preparing accurate [[geological cross sections]] for reservoir development and planning.

Important differences exist, however, between cross-borehole seismic velocity images and sonic logs. Sonic logs usually measure velocity of sound in rocks at very high frequencies (5 to 40 kHz), whereas seismic tomography measures the velocity of sound at seismic frequencies, usually in the frequency range of 20 Hz to as high as several kilohertz. Sonic logs represent the measurement of velocities at the wellbore and are usually plotted as a continuous curve in depth. Because seismic tomography measures the two-dimensional velocity field between the wellbores, it is usually represented by a color-coded map in which a color is assigned to the seismic velocity at each point. This map, or plot, is referred to as a ''tomogram''. Other displays such as contour plots can also be used, but this is not common.

Important differences exist, however, between cross-borehole seismic velocity images and sonic logs. Sonic logs usually measure velocity of sound in rocks at very high frequencies (5 to 40 kHz), whereas seismic tomography measures the velocity of sound at seismic frequencies, usually in the frequency range of 20 Hz to as high as several kilohertz. Sonic logs represent the measurement of velocities at the wellbore and are usually plotted as a continuous curve in depth. Because seismic tomography measures the two-dimensional velocity field between the wellbores, it is usually represented by a color-coded map in which a color is assigned to the seismic velocity at each point. This map, or plot, is referred to as a ''tomogram''. Other displays such as [[contour]] plots can also be used, but this is not common.

==Tomographic data acquisition==

==Tomographic data acquisition==