Deep Single Well EGS Method for Highly Elevated Power and Four Well, 216 GWh Seasonal Storage Capacity

Abstract

Despite geothermal’s potential abundance and the introduction of multi-well enhanced systems (EGS) 50 years ago, both remain as potential power. Through an innovative reconfiguring of EGS in HDR, this paper presents fundamental refinements and substantive baseload production levels making HDR geothermal highly scalable, even to climate impact levels. One novel application of the reconfigured EGS includes grouping four wells’ early production into single or paired plants, supplying three months, 30 MWe per well seasonal and replenishable energy storage. The paper’s objective is to demonstrate realizable long-term clean energy abundance by use of the innovative Deep Geothermal System, or “DGS” method, as supported by decades of subsystem field experience and by recent simulation-based design, performance evaluation, and optimization. DGS reconfigures the traditionally redundant directional or horizontal drilling of multi-well EGS into one substantially deeper vertical well, thereby accessing 50% higher average heat and maximizing per-MW drilling investment. DGS drilling trajectory is done in a manner that is co-planar with its subsequently induced fracture-reservoir-circuits, enabling full hydraulic communication along the entire well-fracture heights. Long-length flow diverters are constructed horizontally in the fractures, bifurcating them and doubling heat-collecting flow length. The diverters guide flow away and back to the well, superheating fluids over 45 hours’ exposure at depths and heat levels double or more that of traditional practice. Tuning of the co-planar hydraulics, in concert with strategic placement of the diverter, enables full control over reservoir’s hydraulic behavior and heat extraction from some 560 hectares (1380 acres) of total system geothermic rockface having 150oC to 400oC and higher heat. Simulation by Computational Fluid Dynamics (CFD) and conjugate heat transfer analyses predicted well production temperatures and output over various rock thermal gradients, fracture dimensions, separation, inlet temperatures, and flow rates. Analyses also showed high-early per well baseload nearing 120MWt by fully sweeping an optimized count of 15 massive, highly separated reservoirs. Net early well output exceeds 30 MWe, as no parasitic injection or significant cooling loads are required in the vacuum driven DGS surface inlet. Analytical work also revealed a roughly optimal 335-meter reservoir separation enabling high level baseload heat replenishment while balancing the practical aspects of overall installation design, deep well construction, economics, and sustainability. A 15 to 20 MWe range baseload output occurring for some 20 years was also shown prior to entering steady state production. Extension of the analytical work further revealed DGS’ ability to deliver 30 MWe as baseload stored energy delivery on a three-month seasonal basis. Thermal recovery occurring for the balance of the year ranged from 92% to in excess of 98%, depending on well spacing and effective rock volumes. The innovative DGS single well HDR geothermal method is not only novel, but revolutionary. DGS technology obsolesces orders more costly and less productive EGS designs requiring two or more wells per location-output. Geothermal’s promises are shown realizable by the type of work presented in the paper – and in new ways.