| Abstract |
Geothermal energy generation from hot dry rock is far beyond its potential in the U.S. and the world. EGS is the most promising energy source yet the least successful among all renewable energy forms. There are many reasons: (1) high risks from largely unknown geologic variables; (2) faults in the design concepts of currently used solutions relying on fracture opening partially by fluid pressure, making the joint’s aperture an operational variable and thus inherently projecting seismic activities with changing pressures and temperatures; (3) inherent loss of coolant water and energy due to excessive injection pressures as a consequence of the faulty concept, abysmal fracture aperture, and consequent large circulation loss in the currently known EGS solutions. A new, robust EGS (REGS) technology tryout is underway with innovative fracture permeability creation and control. The geometry, aperture support technique and coolant fluid flow isolation system are all robustly planned and created according to an invention. The new elements of the REGS technology are step-by-step tested and demonstrated in an international research cooperation with researchers from the USA and the EU. Planning for small-field-scale, directional drilling and fracturing experiments are underway to achieve a planar wing fracture or fractures osculating along the well trajectory at shallow depth. Laboratory-scale, hardening grouting injection experiments are built to demonstrate the creation of a central support island in each planar wing fracture. Numerical models are developed to scale the experimental results for the field-scale design of the REGS. Small-scale, experimental studies of Well-Fracture-Well fluid circulation experiments are used to verify the numerical model results for upscaling. Predicted scenarios are studied with scaled numerical models for full-scale REGS applications for wide-scale applications in (a) electrical power generation; and (b) heating use in communal or industrial examples. The tests are expected 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. The key to energy extraction is the zonal isolation of fracture flow by a grouted, blocking island between injection and extraction points of any planar fracture, forcing the coolant fluid away of the island to sweep large surface area of the planar fracture for heat exchange. The key to the creation of a series of large, planar, wing fractures is a directionally-drilled well to follow each planar fracture, intersecting it at multiple points around a section at which the fracture approximates the osculating plane of the well. The key of the robustness is the step-by-step construction of a REGS with: directional drilling; wing-type fracturing; testing for connectivity of each planar, wing fracture with the well; continuation of the construction and testing of a series of wing fractures along the directional drilled well whereas the well direction is continuously adjusted (if needed) to the planar directions of the fractures; and completion of the series of wing fractures with zonal insulation in each planar fracture by implanting (injecting) a grouted, blocking island between the injection and extraction sections of the well connections to each wing fracture. The paper reports the new results from the laboratory-scale REGS tests and their numerical scaling models; as well as the design of the field-scale experiments in a well drilled in hot, dry rock. |