A new indicator is presented which allows major local tectonic features to be determined from a single well. The only measurement required, besides mud filtrate resistivity and temperature, is the SP log. The information which can be determined from this indicator includes:

  1. Location of fault zones.

  2. Location of compaction stress changes.

  3. Location of abnormal pressures.

  4. Location of permeable sands of significant extent.

The method is simple and may be cross-checked with the density or travel time log. It involves several simple principles:

  • (water salinity) (shale porosity) = constant

  • (shale porosity) = (overburden-hydraulic pressure) Water salinity may be accurately determined from clean sands, and a complete well profile is needed to make an analysis.

Several analyses are made, where the various stresses have been confirmed. Mathematical theory and laboratory results are also presented. 34

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