Energy potential of a single-fracture, robust, engineered geothermal system

Abstract

Engineered Geothermal Systems (EGS) are promising, but high-risk targets for baseline energy generation. Technology breakthrough is needed to lower the high risks from largely unknown geologic variables and the limited control of the coolant flow field underground. A new, robust EGS (REGS) arrangement and creation technology is reviewed featuring innovative fracture opening, stabilization and permeability control. The geometry, aperture support technique and coolant fluid flow isolation system are all robustly planned and created according the inventive concept. The new elements of the REGS technology are (1) the step-by-step creation, control, and tests of hydraulic fracturing to achieve a planar wing fracture or fractures osculating along the well trajectory; (2) fracture stabilization by hardening grouting injection to create a central support island in each planar wing fracture for zonal isolation; and (3) well-fracture-well fluid circulation for geothermal energy extraction from single, or clustered planar fractures as geothermal heat exchangers. The paper reviews ongoing tests to prove the key components of the REGS geologic heat exchanger with stabilized, large fracture aperture and controlled flow zones for minimized opening pressure loss, seismicity and maximized energy extraction. Flow fields and heat transport are reviewed around zonal isolation of fracture flow by a grouted, blocking island for heat exchange. The robustness is reviewed for the step-by-step construction of a REGS. The paper reports new results from using numerical, coolant flow and heat exchange models to demonstrate the geothermal energy potential of a single REGS well drilled in hot, dry rock.