A REACTIVE TRACER METHOD FOR THE MEASUREMENT OF SPECIFIC SURFACE AREA IN EGS RESERVOIRS

Early thermal breakthrough is an issue of concern in the geothermal industry, especially with regard to engineered geothermal systems (EGS). Determination of the specific surface area (SSA) of the fluid/rock interface in an EGS is vital to predicting early thermal breakthrough. An approach to this problem involving the application of tracers with different sorption properties (lithium, bromide, and deuterium) is presented. Upon injection into a reservoir, these tracers react along the fluid/rock interface to varying degrees. The resulting breakthrough separation at the extraction well can be used to derive SSA by applying a modified form of the advection-dispersion equation. For proof of concept, field tests were conducted in a sandstone bedding-plane fracture near Chazy, New York. Results showed minimal breakthrough separation, indicating insufficient sweep of the fracture area, and that lithium was not an ideal tracer in this medium. However, a relative measure of SSA can still be derived