FORSTER, A., GeoForschungsZentrum, Potsdam, Germany; and D. F. MERRIAM, Kansas Geological Survey, The University of Kansas, Lawrence, KS

ABSTRACT: Preliminary Temperature Field Interpretation in the Southern Part of the Central North American Rift System (CNARS) in Kansas

An assessment of temperature measurements available from wells provides information on possible relations between the observed geothermal gradients and geological features. The question is whether the southern extension of the Central North American Rift System (CNARS) could have an influence on the observed thermal regime caused by different heat conductivity and heat production in relation to the surrounding basement rocks or whether structural highs of the basement could be related to the temperature field. In order to quantify these relationships and to get an insight into the function of the temperature field two approaches were used (1) a map comparison technique based on algebraic methods, and (2) the numerical computation of theoretical temperature-depth models based on conduc ive heat transfer. The temperature field information usable for the map comparison is different in response to different measurements (unequilibrated BHT and temperatures from logged measurements in equilibrium) as well as to different depth levels used in averaging the temperature gradients.

Derived from modeled results (plotted isotherms in cross sections), a close relation between gradients and thermal conductivity of the sediments is confirmed by different temperature-depth distributions. The most noticeable effect on the geothermal field as noted quantitatively from the map-comparison study is the thickness of the outcropping Permo-Pennsylvanian because of their different heat conductivity. The eastward increase of the gradients is related inversely to the total sediment thickness but mostly recognizable using the shallow temperature gradients. This dissimilarity gives additional evidence for a close linkage between gradients and heat conductivity of the sediments in which the temperature measurements were done. The effect caused by the structure in the deeper (older) units is not important and seems not to be significant nor is the influence of basement composition as indicated by a comparison with geophysical maps. The observed gradient pattern mostly reflects temperature differences caused by the different depth levels (differential heat conditions) used for averaging.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.