Developments in geothermal energy in Mexico—Part thirty-three. Simultaneous determination of the thermal properties of geothermal drill cores

Abstract

Thermal conductivity, thermal diffusivity and specific heat capacity of five drill cores from the Los Humeros and La Primavera geothermal fields were obtained via parameter estimation. The data were obtained by fitting an analytical model to the transient temperature rise caused by a line source of heat of constant strength located along the axis of the samples. The model was obtained from the solution to the problem of an infinite region bounded internally by a hollow circular cylinder with thermal contact resistance at the cylinder surface (J. H. Blackwell, Transient heat flow problems in cylindrical geometry, Ph.D. Thesis, University of Western Ontario Canada, London, Canada, 1952). Results were obtained for fused quartz and a Berea sandstone for calibration purposes and the agreement with known properties for these samples showed maximum differences of 10%. Results obtained for a dry drill core from the Los Humeros field showed a thermal conductivity of 1.36 W m −1 K −1, a diffusivity of 0.54 × 10 6 m 2 s −1 and a specific heat capacity of 0.96 kJ kg −1 K −1. Results for dry drill cores from the La Primavera geothermal field showed thermal conductivities between 1.53 and 2.51 W m −1 K −1 while thermal diffusivity varied from 0.71 to 1.0 × 10 −6 m 2 s −1. Specific heat capacity varied from 0.73 to 1.03 kJ kg −1 K −1. Results obtained for these cores under water saturation conditions showed significant increases in all three properties with the degree of increase being a function of the pore volume occupied by the water.