OVERVIEW

While one part of petrophysics is concerned with the interface with geologists and reservoir engineers in order to produce reservoir models, a further interface exists with the seismologists to ensure that the well data are used to help calibrate and understand seismic properties.

While the preparation of synthetic seismograms to tie log-formation tops with seismic horizons is a long-established technique, recent advances in far-offset seismic processing, combined with the ability to measure shear-sonic transit times, have opened up a lot of new possibilities for facies and fluid determination from seismic data. In this chapter some of these techniques will be discussed.

6.1 SYNTHETIC SEISMOGRAMS

There are two elements to synthetic seismograms. The first is the derivation of the acoustic impedance (AI) from the log data, from which reflectivity may be derived. The second is the conversion of the depthrelated traces from a depth reference to a time reference so they can be compared with seismic sections. From the log data, the following may be derived:

where V _p is in m/s and sonic is measured in ?s/ft.

where ? is in kg/m ³ and density is measured in g/cc.

The AI is given by:

where AI is in kg/m ²/s.

Hence an AI trace may be derived simply from the sonic and density logs. Prior to generating the AI, it is necessary to correct for any washouts; if necessary, editing the logs by hand. It is also necessary to correct the logs for any...