ABSTRACT: Basin Log Temperatures vs. Measured Temperatures

HABERLE, FREDERICK R., Consulting Geologist, Dallas, TX

Interpretation of electric logs, studies of hydrocarbon generation and many other facets of petroleum geology require temperature data for varying depths in the earth. Such temperatures, usually obtained from bottom-hole temperatures recorded during logging operations, are used to calculate a geothermal gradient. Detailed studies reveal that log temperatures are rarely recorded after temperature equilibrium is reached in the borehole and therefore do not accurately measure formation temperature at a given depth. Comparison of temperatures recorded during logging with temperatures recorded after long shut-in periods for production tests indicate that the logging temperatures may be as much as 45 degrees F lower than the true formation temperatures. Study of temperature measurements rec rded after logging and after shut-in periods permit a generalized correction curve to be established for a basin. Such a curve will be unique to that basin.

As there appears to be a general association of geothermal gradient highs with gravity maxima, structures may be indicated by such highs. It is possible to use geothermal gradients as an exploration tool as long as it is remembered that all geothermal gradient highs are not necessarily productive. Higher geothermal gradients above uplifted fault blocks and lower gradients above downfaulted blocks are common. By using geothermal gradients depths to a given temperature may be calculated. If any particular temperature is considered necessary for large scale hydrocarbon generation, productive fields in areas with lower temperatures would indicate either migration or an active tectonic area.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)