Feasibility of deep direct-use heating for district-scale energy systems over the Illinois Basin

This study is assessing the feasibility of using deep direct-use (DDU) geothermal energy to heat agricultural research facilities on the University of Illinois at Urbana-Champaign (UIUC) campus, and its application to other district-scale facilities over the Illinois Basin (ILB). The geothermal system being evaluated would exploit low-temperature brine (<50 degrees C) in the lower part of the ILB extracted using a two well (doublet) system. The surface infrastructure connected to the wells would include heat exchangers connected in parallel to pipelines carrying brine, and fresh cold and hot water. Two geologic formations were initially evaluated as a potential source of heated brine based on pre-initial temperatures and fluid flow rates. At the UIUC campus, the St. Peter and Mt. Simon Sandstones lie at depths of 2202 feet (670 m) and 6190 feet (1887 m) bgs, respectively, and are regionally-extensive and prolific ILB aquifers. Modeling of the geothermal system indicates the aquifers would meet the baseload heating rate at the UIUC facilities, 2 MMBtu/hr (2110 MJ/hr), by pumping approximately 6000 barrels (954 m3) of brine per day. After evaluating the heating requirements of these facilities, it was determined only the Mt. Simon Sandstone could deliver brine that is at or above the target temperature of 110 degrees F (43 degrees C). A life-cycle cost analysis (LCCA) is being conducted to estimate the total cost over the life of the project. Ultimately, the system would reduce greenhouse gas emissions and fresh water usage on the UIUC campus and contribute to the University's goal of becoming carbon neutral by 2050. Multiple system designs are being analyzed to maximize: 1) the performance of the geothermal system, 2) energy efficiency, and 3) cost recovery. Undertaking this high-level evaluation will provide a benchmark for adopting DDU technologies in district-scale energy systems at other educational campuses, industrial and medical facilities, and military installations over the ILB.