Stanford Geothermal WorkshopFebruary 9-11, 2026

Mapping propped fractures and understanding proppant distribution within fractures is critical for the success of Enhanced Geothermal Systems (EGS) projects. Borehole electromagnetic (EM) measurements offer a promising method to image proppant distribution. Electrically conductive (EC) proppant enhances the EM contrast between propped fractures and the surrounding formations. However, EC proppants are expensive, necessitating their use in small concentrations mixed with normal proppants. Electrically conductive fluids are needed to further increase the EM response. This study investigates the use of carbon black suspensions as an alternative to traditional electrolytes to enhance the electrical conductivity of fracturing fluids while addressing the challenges of salt precipitation and corrosion. In addition, the effect of carbon black on fluid rheology was evaluated under high-pressure and high-temperature conditions to reduce the thermal effect on the fracturing fluid viscosity, to improve proppant transport and distribution within EGS fractures. Laboratory systems were designed to quantify the rheological properties and electrical conductivity of EC proppants and carbon black suspensions at varying concentrations under EGS conditions. Results show that carbon black suspensions can significantly increase the electrical conductivity of fracturing fluids. Low concentrations of CB (≈1 wt%) were tested at varying temperatures up to 200 °C, resulting in a 40% increase in the solution’s viscosity. Using 1% CB increases the electrical conductivity of the solution up to 0.5 s/m at 200 °C and 2000 psi. This study verifies the potential of carbon black suspensions for improving fracture mapping in EGS through borehole EM measurements while mitigating the drawbacks of electrolyte-based solutions and simultaneously improving the fluid viscosity performance under high-temperature geothermal conditions.

Topic: Enhanced Geothermal Systems