THE EFFECTS OF TEMPERATURE DEPENDENT THERMAL PROPERTIES IN MODELING GEOTHERMAL GRADIENTS OF THE ILLINOIS BASIN
We measured D using the contact-free laser flash analysis (LFA) method, and CP using differential scanning calorimetry (DSC) from 25°C to 300°C, for a series of well-characterized mudstones collected from drill core in the Illinois Basin. We found that: (1) mineralogy affects D more than texture or elemental composition, (2) mudstones have a lower D than sandstones, limestones, or dolostones, (3) the k of mudstones decreases between 4% and 18% from 25 to 300˚C, which is a smaller decrease than for other sedimentary rocks, and (4) our measured k values are not reproduced well by current models that estimate kbased on composition and texture.
The new values of temperature dependent thermal properties were used in seven one-dimensional, conductive heat flow models of past and present geothermal gradients in the Illinois Basin. There is good agreement between the models and present-day borehole temperature (BHT) measurements. The temperature effect on k is greatest at low temperatures, demonstrating the importance of using temperature dependent thermal properties when modeling geothermal gradients of sedimentary basins. The variation between measured and predicted k values suggests more high temperature measurements of thermal transport properties are needed.