Variations in Thermal Properties With Lithology in the San Joaquin Valley, California

SPE Member Geothermal gradients and thermal conductivities were measured in three oil-saturated formations having different lithologies at one location in the southern San Joaquin Valley, California. The three lithologies in order of increasing depth were a sandy conglomerate, diatomite, and porcelanite, respectively. porcelanite, respectively. The geothermal gradients were measured with arrays of thermocouples in dry observation wells prior to steam injection in the area. The measured gradients for the three lithologies were 1.8, 5.8, and 2.3 degrees F/100 ft (33, 106, and 42 mK/m), respectively. The geothermal gradient through the sandy conglomerate and the porcelanite are consistent with published valued for this area (Sass, J.H., Galanis, S.P., Jr., and Munroe, R.J. : Measurement of Heat Flow by a Downhole Probe Technique in the San Joaquin Valley, California (1982) USGS Open-File Report 82-819), but the gradient through the diatomite is significantly higher. Thermal conductivities of these formations were measured on core taken from nearby wells. Because thermal conductivity varies with porosity and oil saturation, core samples were selected for each lithology that had values equal to the average of their respective formations. The thermal conductivities were measured using the steady-state, divided-bar method at 150 and 300 degrees F (66 and 149 degrees C). The measured values for the sandy conglomerate at the low and high temperatures values were 0.71 and 0.77 btu/(hr-ft2- degrees F/ft) (1.22 and 1.33 W/m-K), respectively. The values for the diatomite were 0.35 and 0.51 Btu/(hr-ft2-0F/ft) (0.61 and 0.88 W/m-K), respectively, while the values for the porcelanite were 0.63 and 0.67 Btu/(hr-ft2-0F/ft) (1.09 and 1.16 W/n-K), respectively. The thermal conductivity of the diatomite was considerably lower and its temperature dependence was greater than that of the other formations. These data are consistent with published values for other sedimentary rocks (Anand, J., Somerton, W.H., and Gomaa, E. : Predicting Thermal Conductivities of Formation from Other Known Properties, Soc. Pet. Engr. J. (1973) Vol. Properties, Soc. Pet. Engr. J. (1973) Vol. 13, No. 5, pp. 267-273). The geothermal gradients and thermal conductivities were multiplied to yield the local geothermal heat flow. The formation thermal conductivities were determined by linearly extrapolating the measured conductivities to the temperatures at the midpoint of each formation. For the sandy conglomerate, diatomite, and porcelanite, these temperatures were 90, 100, and 115 degrees F (33, 38, and 46 degrees C), respectively. The resulting heat flows were 0.012, 0.016, and 0.015 Btu/(hr-ft2)(38, 50 and 47 mW/m), respectively. The difference between these numbers are from the uncertainties in the measured gradients and conductivities. These heat flows are consistent with published values for the area (Gosnold, W.D. and Fischer, D.W. : "Heat Flow Studies in Sedimentary Basins," Thermal Modeling In Sedimentary Basins. Burrus, J. (ed.), 1st IFP Exploration Research Conference, Carcans, France, (1985). This study has demonstrated that thermal properties of oil saturated rocks can vary properties of oil saturated rocks can vary significantly with lithology, particularly where diatomite is present. Such variations, if not properly accounted for, can lead to errors in the estimated formation temperatures, fluid properties, and heat flows. P. 593