Estimating Thermal Conductivity in Sedimentary Basins Using Lithologic Data and Geophysical Well Logs

Abstract

ABSTRACT A method for estimating in-situ thermal conductivity profiles in oil and gas wells is advanced to rectify a major shortcoming in thermal analyses of sedimentary basins. Thermal conductivity estimates are made in a two-stage procedure and are based on a model for the conductivity of mixtures and input data from lithological and geophysical logs. First, rock matrix conductivity for an arbitrary depth interval (i.e., drill cuttings sample interval, which is about 3 m) is determined from the laboratory-calibrated conductivities and volumetric representation of its individual lithologic components using a geometric mean model. In-situ conductivity is then estimated by a second application of the model, correcting for temperature and porosity determined from geophysical logs. The method is illustrated for three Uinta basin (Utah) wells that penetrate a series of Tertiary sandstones, shales, and muddy carbonates. Detailed lithologic descriptions, together with sonic and neutron logs, were digitized and used for estimating in-situ conductivity. The validity of the method was tested by comparing the prediction against laboratory measurements on 565 samples from the same wells. Rock matrix thermal conductivity ranges from 1.6 to 6.8 W/m/K and is predicted within 20% of the actual measurement for 90% of the samples. Both in-situ conductivity values and variations for a given lithologic unit are reduced at increased porosity and increased temperature. Thermal conductivity nomograms are presented as useful tools to predict directly the in-situ thermal conductivity of a formation from a well log signal.