A technique for improving pseudo-synthetic seismograms generated from neutron logs in gas-saturated clastic rocks

Shih Ling Kung, Charles Lewis, Jong Chang Wu

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

In clastic and carbonate rock sequences, the neutron and sonic log curves usually deflect in a similar fashion. Moreover, in some cases the two curves can be overlain and they generally appear to mimic each other, with variations between them only in the amplitudes of the two curves. This descriptive correlation is the basis of direct cross-plot techniques used to convert a neutron log into a pseudo-sonic log, which can then be combined with a density log to create a pseudo-synthetic seismogram. Unfortunately, the seismograms produced in this way may not match the standard synthetic seismograms produced from the sonic and density logs if the 'gas effect' is not taken into account. In order to correct for the gas effect, the inter-log correlations between the compensated neutron log (CNL) and the borehole-compensated (BHC) sonic log curves from a well in Taiwan were carefully examined. Then, we developed a technique for transforming the CNL log into a pseudo-BHC log by splicing together several continuous sandstone intervals in which the gas effect could be identified from the scattered data on the cross-plot of neutron porosity versus sonic interval transit time. Based upon our results, application of the new composite transform method yields a pseudo-synthetic seismogram that better matches the standard synthetic seismogram (made from the sonic and density logs) according to frequency, amplitude and polarity. This gas correction technique may be particularly useful in oil and gas exploratory and development areas where neutron logs are more prevalent than sonic logs or where sonic logs are scarce.

Original languageEnglish
Article number035015
JournalJournal of Geophysics and Engineering
Volume10
Issue number3
DOIs
Publication statusPublished - 2013 Jun 1

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geology
  • Industrial and Manufacturing Engineering
  • Management, Monitoring, Policy and Law

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