Positive temperature anomalies associated with fluid-migration paths are expected effects within a compacting and dewatering sediment pile. However, temperature anomalies are also produced by lateral variations in thermal conductivity of the sediments. Using established relations between thermal conductivity and seismic velocity, an estimate of regional heat flow, and average surface temperature, it is possible to estimate the local geothermal gradient (due to solid state, one-dimensional conduction) from sonic logs or downhole velocity surveys. Subtraction of such calculated temperatures from corrected bottom-hole or log temperatures produces mappable residual temperature anomalies which can be interpreted as effects of active upward fluid migration. Mapping of such residual temperature anomalies and comparison with structural setting provide a stronger tool for interpreting routes of water (and perhaps hydrocarbon) migration, than using temperature values without removal of conductive effects. The procedure is analogous to removing a predicted regional gravity Field to produce residual gravity anomaly. Interpretations are strengthened by mapping calculated fluid pressure and salinity anomalies which might also be attributable to fluid movement.
Examples from the Louisiana Gulf Coast Miocene illustrate the application and promise of the technique. Residual temperature anomalies occur close to faults, suggesting the potential importance of such structures as routes for fluid escape. The method also provides a means of interpreting correspondence of thermal highs with structural highs as products of either conductive focusing or fluid movement up structure, though two- or three-dimensional modeling is required.