NO CURRENT OR BURGEONING GEOTHERMAL PRODUCTION METHOD IS GLOBALLY SCALABLE AGAINST CARBON.
Limitations of the Four Primary Geothermal Extraction Methods Are Described:
HYDROTHERMAL
The original and highest producing geothermal type, natural hydrothermal / steam sources are quite rare, present under only 0.15% of land.
- Drilling ten exploratory boreholes are required to locate a potential resource
- Successful drilling is not guaranteed even after discovery, contributing to the requirement of several years development time before revenue commences
- Natural water supplies are vulnerable to depletion or regulatory restriction
- Natural fluids may be highly corrosive, requiring use of costly alloys in the production infrastructure
ENHANCED GEOTHERMAL SYSTEMS (EGS)
Under development since 1973, but not commercially detectable, traditional Enhanced Geothermal Systems (EGS) suffers six fundamental weaknesses:
- The requirement for two or more wells doubles drilling cost
- Required deviated (non-vertical) drilling, further inflates cost 50% - 60%
- Deviated drilling limits reaching utility scale depths and temperatures -- EGS accesses half the heat at twice the cost
- Hydraulic reservoir stimulation at the shallow depths may cause earthquakes, although extremely rarely
- Shallow geology contains natural fractures that cause excessive water losses, to 60+%
- EGS’s minimal intersecting well-reservoir configuration causes hydraulic and thermal short-circuiting between the wells, where as little as 10% of the available heat is produced
LOOPS
Simple circulating loops, except when placed in uncommonly hot rock, do not produce scalable power. On average, approximately 0.5 gross MW is generated from average 300oF rock per loop-mile, making loops mostly suited for direct use building heat and similar.
SUPERDEEP / SUPER HOT / SUPER CRITICAL FLUID (SCF) EXTRACTION
SHDR/SCF-type wellbore creation methods generally involve rock vitrification in 750+oF rock, with some processes claiming sinking capabilities to 10 miles or greater depth. These systems rely on thermal disintegration as means of borehole excavation, likely a decade+ from usefulness, given the realities of field environments and market adaptation laggings. Once a well volume is evaporated, a glasslike borehole wall is left embrittled, unable to withstand the weight and other complex stresses of many miles of overlying rock compressing, twisting, and bending this “glass”. Typically proposed as a multiple well production scheme, SHDR systems provide no means of connecting to or creating a useful reservoir. Except with installation of DGS type reservoirs, no scalable heat transfer effectiveness can be expected. This is because, first, natural permeability closes under high rock weight. Second, induced reservoir-fractures propagate as a narrow width, vertically oriented plane that is virtually impossible to connect to a second well unless it is directionally drilled – yet another challenge in the extreme conditions. Further, there are currently no practical fractured-reservoir stimulation fluids to survive the 1000+oF environments targeted by proponents.