Application of hydraulic and thermal stimulation techniques at Raft River, Idaho: A DOE enhanced geothermal system demonstration project

The Raft River geothermal field located on the Idaho-Utah border is the site of a Department of Energy (DOE) Enhanced Geothermal System (EGS) demonstration project. The field consists of four production and four injection wells drilled into Precambrian metamorphic rocks. The purpose of this project is to stimulate a sub-commercial well, RRG-9 ST1, using a combination of hydraulic and thermal techniques. These stimulations have led to a significant improvement in the performance of the well. Over time, injection rates have increased from near zero in June 2013 to the current flow rates of 3546 Lpm (937 gpm) (February, 2016), at constant or decreasing wellhead pressures. This injectivity improvement was achieved through a combination of three hydraulic stimulations accompanied by thermal contraction of the surrounding rocks from continuous injection of sub reservoir temperature water from the geothermal plant. Geological studies, borehole imaging, and temperature surveys indicate that the water injected into RRG-9 ST1 flows into a fracture zone at 1722 m MD (5650 ft.). It is suggested this fracture zone connects with a larger northeast-trending shear zone within the Elba Quartzite referred to as the Narrows Zone. This zone acts as both a barrier and a conduit to fluid movement within the field. Both thermal and hydraulic stimulation effects contribute to the increase in permeability and injectivity of the well.