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The reconciliation of measurement differences between seismic and well-log derived data is a critical issue in exploration. Both data sets contain "apparent ground truth" information, but neither is free from errors. Because well logs can be considered as in-situ measurements and seismics are considered as surface sensing measurements, the major physical differences between the two are: (1) the volume of rocks the data represent, and (2) the presence of wave propagation effects for the seismic method.
The conventional method of reconciliation is through the use of the synthetic seismogram. The geophysicist simulates the seismic signature of the given earth model defined by sonic and density logs, and attempts to match the synthetic with the seismic trace. In practice, the character and travel-time of the events from the seismic trace usually do not match those from synthetic seismograms. In addition to the physical differences between the measurements, the mismatch can be attributed to : (1) one-dimensional model used to generate the synthetic seismogram, (2) use of an approximate solution to the wave equations in synthetic seismogram calculation, and (3) inability to simulate seismic processing effects in the synthetic seismogram generation.
Some of the reconciliation methods show that (1) free surface multiples and interbed multiples remaining on seismic data can be identified by using VSP-processed data; (2) observations that seismic times are longer than integrated sonic times are reconciled by determining and comprehending multiples, Q, and dispersion factors; and (3) full waveform offset-dependent modeling is essential to comprehend and understand VSP, seismic, and integrated sonic-log derived differences.
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