EVALUATING THE USE OF LITHOLOGY AS A GUIDE IN ESTIMATING THERMAL CONDUCTIVITY VALUES FOR GEOTHERMAL RESOURCES

Geothermal energy provides an environmentally friendly alternative to standard methods of power generation and building heating and cooling. Knowledge of the rock thermal conductivity is essential for proper resource assessment and system design. One approach to estimate thermal conductivity is to use lithologic information. To better inform this lithological approach, we evaluated recently collected thermal conductivity data in Massachusetts and New Hampshire. We also took a closer look at the mineralogy-based method of Benson (2009). While it is possible to specify likely upper and lower bounds along with state and formation wide averages for different lithologic classifications, the range can be large, and individual site data varies too significantly for the means to be useful. One limitation of current data is that it represents a physical scale much smaller than the scale of interest, and potentially smaller than the scale of the natural variability. Further research is needed to assess if variability in thermal conductivity increases or decreases with the scale of measurement, and to develop a more appropriate representative elementary volume in order to better facilitate this effort.