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:
Location of fault zones.
Location of compaction stress changes.
Location of abnormal pressures.
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