Temperature Gradient in Pechelbronn Oil-Bearing Region, Lower Alsace: Its Determination and Relation to Oil Reserves

Abstract

Numerous temperature measurements have been made during the last ten years in the Pechelbronn oil-bearing region, to aid in the search for petroleum deposits. However, the results of the study of approximately 500 measurements clearly show that the isogeotherms are influenced primarily by the tectonic structure of the Rhine Valley graben. They show a nearly regular rise from the edges to the central part of the graben; also not uncommonly they approach one another. Such increase of temperature is especially marked in the fault zones. Seemingly, the isotherms are not influenced by larger or smaller oil accumulations; therefore, the presence of oil can not be looked upon as the cause of the relatively elevated temperature. It is perhaps possible to explain the rise of temperature toward the central part of the graben by a gradual change in the nature of the deposits. Coarse-grained sandy beds of the graben edges are gradually replaced toward the center by increasingly finer sands, and finally by finely laminated marls. It is possible that these finest deposits act as a sort of protective cover against the loss of heat. This suggestion would also explain the increase of temperature and the accumulation of heat along the faults, as it is possible to suppose a stronger increase of temperature in the direction of the dislocation in the strata. This suggestion is strengthened by the fact that the especially high horsts are characterized by temperature maxima on the isothermal map.