Toward More Efficient Heat Mining: A Planned Enhanced Geothermal System Demonstration Project

Abstract

AltaRock, in partnership with NCPA, has been working on a project to demonstrate new technology aimed at lowering the cost of an Engineered Geothermal System (EGS). The stimulation target is a hot, intrusive body in Northern California underlying an existing geothermal resource. An EGS creates or enhances a geothermal reservoir by shifting critically stressed fractures in hot rock through hydroshearing, and then cycles water through the fractures to mine the in-place heat. The goal of the project is to create multiple independent fracture zones from a single well in order to increase the aggregate flow rate without increasing the pressure drop through the system. Because well drilling and completion together represent the biggest single cost of an EGS, the ability to increase flow rates without resorting to additional wells would significantly reduce the cost of this power-generation technology. A microseismic array has been installed to monitor the fracturing progress and post-stimulation development in near real-time. New methods have been lab tested and modeled numerically to evaluate reservoir heat-exchange area, flow-paths, and fracture connectivity. These will be deployed in the field during flow back testing of the stimulated zones. Fluid chemistry will be monitored for chemical changes.