High Resolution temperature logs in a petroleum setting: examples and applications
David D. Blackwell and Graeme R. Beardsmore,
Department of Geological Sciences, Southern Methodist University, Dallas, Texas, 75275-0395,
Richard K. Nishimori, and Richard J. McMullen, Jr.,
Mobil Technology Company, PO Box 650232, Dallas, Texas 75265-0232
in Geothermics in Basin Analysis, Computer Applications in the Earth Sciences,
Edited by Andrea Forster and Daniel F. Merriam, Plenum Press, New York and London, pp. 1 - 34, 1998.
Examples of high resolution temperature logs measured in oil and gas fields in the United States are presented and the pertinent features useful in basin analysis are discussed. We point out that wells suitable for equilibrium or near equilibrium temperature logs are commonly available and we describe by examples criteria for the evaluation of the quality of a high resolution temperature log. Examples of temperature gradient logs from two fields in the Paleozoic age Anadarko Basin in Oklahoma, one field in the Cenozoic Gulf Coast Basin, and one field in the Mesozoic/Cenozoic Sacramento Basin in northern California are described and their application to the analysis of basin thermal structure discussed. The major criteria that can be used to evaluate the quality of the log are level of (temperature) noise, presence/absence of negative/zero gradient sections, degree of correlation with other geophysical logs, and well to well comparisons. Even logs that are not in complete equilibrium contain significant information compared to a typical set of BHT points. The development of memory P/T tools and their deployment in the field for production logging means that the potential now exists for routine collection of high resolution temperature data in hydrocarbon settings world wide. Because the thermal regime of many boreholes in producing fields may be closer to equilibrium than has been thought in the past the new temperature capability can be used in a pratical way. High resolution logs can furnish detailed information on the gradient, the ratios of the thermal conductivity values in hard-to-sample lithologies to those in lithologies easier to characterize, and ultimately more precise understanding of the thermal regime (whether conductive, convective, etc.) in individual wells and sedimentary basins. So the use of these types of high resolution logs can now be added to the petroleum explorationistís data sets to be used in basin thermal analysis as an important new source of information that can be used to increase the precision and/or estimate the errors of the models developed based on conventional BHTís and cuttings measurements.