Crain's Petrophysical Handbook - CASE HISTORY -- EDITING WITH RESISTIVITY DATA

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CASE HISTORY -- EDITING WITH RESISTIVITY DATA

Editing with Resistivity Data Editing with Fisher and Good Editing with Faust and Smith

MODELing with resistivity data
This Section contains a case histories using resistivity methods for editing and illustrates the differences obtained from various approaches, as well as the dramatic reduction in noise on the final synthetic seismograms. Refer to other Sections of this Chapter for the mathematical details.

Case History - Fisher Good Editing
This example shows the effect of the Fisher-Good method on noisy sonic and density data. The illustrations show:
   1. original and edited sonic
   2. original and edited density
   3. synthetic from original sonic and density
   4. synthetic from edited sonic and density

Original and edited sonic log

Original and edited density log

Synthetic from original logs

Synthetic from edited logs

The close match of the edited logs to the original (where no editing was required) demonstrate the calibration of parameters. Rational logs are generated where bad hole effects seriously degrade both original sonic and density. The synthetic seismogram has no spurious reflections and horizon time picks are reliable.

The method is described in more detail in "An economic approach to sonic error corrections: The EASElog process"; Fischer, J.G., Good, W.F.; p. ??, SEG 1985. This example was prepared by Harold Ryan using the seismic modeling module of the author's LOG/MATE software package.

Case History - Faust and Smith Editing
These examples show the results of using Wyllie time average (response equation), Faust, and Smith editing techniques to four US cases. The log plots show:
   1. gamma ray log
   2. resistivity log
   3. computed lithology
   4. original sonic and Wyllie edited sonic
   5. original sonic and Faust edited sonic
   6. original sonic and Smith edited sonic
   7. error between original sonic and Wyllie edited sonic
   8. error between original sonic and Faust edited sonic
   9. error between original sonic and Smith edited sonic

Faust, Smith, and Wyllie editing - onshore Gulf Coast, Texas

Faust, Smith, and Wyllie editing - offshore Gulf Coast, Texas (upper) and Fort Worth Basin, Texas (lower)

Faust, Smith, and Wyllie editing - East Texas

It is clear that reasonable sonic, and also density if needed, can be generated by these techniques. The error traces help identify the places to concentrate effort. Places where the error is small identify reasonable good original log data and where parameters can be refined by successive iterations. These illustrations are from "In search of the well tie: what if I don't have a sonic log?"; Adcock,S.; SEG Leading Edge, p. 1161-1164, Dec 1993.