Table of Contents
GEO-PRESSURIZED HOT DRY ROCK: Hot dry rock is an abundant source of heat available for use. A concept for extracting valuable amounts of heat from HDR originated at Los Alamos National Laboratory in 1970, and researchers at the Laboratory have received a US patent covering it
| Attribute | Description |
|---|---|
| Basic Definition | The Earth’s internal heat, is primarily from radioactive decay of isotopes. |
| Depth | Typically more than 3 kilometers beneath the Earth’s surface. |
| Heat Source | The Earth’s internal heat is primarily from radioactive decay of isotopes. |
| Method of Heat Extraction | Water is injected into the deep rock fractures, where it gets heated and then extracted as steam or hot water, which is then used to generate electricity. |
| Temperature Range | 150°C to 300°C (can vary based on the location and depth). |
| Reservoir Requirements | Requires no natural permeability or fluids. The system is engineered by fracturing the rock and injecting water. |
| Plant Type Used | Binary cycle power plants are commonly used because of the moderate temperature range. |
| Advantages | 1. Can be developed in regions without natural geothermal reservoirs.<br>2. Large potential as most of the Earth’s crust is hot dry rock.<br>3. Sustainable and low greenhouse gas emissions. |
| Challenges | 1. High initial costs for drilling and fracturing.<br>2. Potential for induced seismic activity.<br>3. Need for significant water resources for the extraction process. |
| Environmental Impact | A geothermal energy extraction method involves man-made fractures in deep underground rocks, allowing water to circulate and absorb heat from these hot rocks. |
| Examples | Experimental and early commercial plants have been developed in regions like France, Australia, the UK, and the US. |
Energy from Rocks History
Konstantin Tsiolkovsky (1898) had an idea of the extraction of heat from deep dry and hot rocks which is also described by Charles Parsons in 1904 and Vladimir Obruchev in 1920. The Fenton Hill Project is the first system to extract HDR heat from an artificially formed tank that was created in 1977.
Energy from Rocks
Although often confused with the relatively limited hydrothermal resource already disproportionately marketed, HDR heat is exceptionally different. By comparison, hydrothermal energy production can only draw on hot fluids that already exist in the earth’s crust. The HDR system (consisting of the pressurized HDR tank, surface holes, and surface injection pumps, and associated piping) recovers heat from the Earth through dry regions via a pressurized closed-loop circulating fluid.
This fluid, injected from the surface below the top, opens pre-existing joints within the base rock, creating an artificial reservoir that can reach the size of one cubic kilometer. The fluid injected into the tank absorbs heat energy from the high-temperature rock surfaces and is the carrier to transport the heat to the surface for practical use.
GEOPRESSURIZED HOT DRY ROCK technology
Drilling and pressurizing
According to Brown’s description, an HDR geothermal energy system is first developed using conventional drilling to access a deep, hot region of basement rock. Once the chosen area has been determined, it does not contain gaps or open joints (by far the most common situation), an isolated section of the primary well is pressurized to a level high enough to open previously sealed joints within the rock mass.
With continuous pumping (hydraulic stimulation), a large region of stimulated rock (the HDR reservoir) is created, which consists of an interconnected series of joint flow paths within the rock mass. The opening of these flow paths causes the generation of seismic signals (micro-earthquakes). Analysis of these signals provides information about the situation and size of the developing field.
Planning and control of GEOPRESSURIZED HOT DRY ROCK
Since the pressure expansion forms the pool of joints, the elastic response of the surrounding rock mass leads to a strongly compressed and sealed rock neighborhood at the periphery, making the HDR pool confined and contained. Therefore, this tank is fully designed. The physical characteristics (size, depth at which it is created) also exist because the operating parameters (injection and production pressure, production temperature, etc.) can be pre-programmed and strictly controlled.
Production wells
Typically, an HDR tank forms in an ellipsoidal shape, with its longest axis orthogonal to the almost negligible amount of the Earth’s main voltage. This pressure-stimulated region is accessed from two production wells at the intersection of the HRD field near the elongated ends of the stimulated area. In most cases, the starting hole serves as an injection to the other wells of a pressurized water circulation system.
GEOPRESSURIZED HOT DRY ROCK operation (HDR)
During operation, fluid is injected at pressures high enough to open the interconnected network of couplings against global stresses and to effectively circulate fluid through the HDR tank at high speed. However, during routine energy production, the injection pressure is kept slightly below the extent that can cause further pressure stimulation from the surrounding rock mass to maximize energy production by limiting additional reservoir growth.
Productivity
In newly created open joints within the HDR tank, the volume is less than one percent of the size of the pressure-stimulated rock mass. As these seals still expand the pressure, the overall flow impedance through the tank becomes very low, resulting in high thermal productivity.
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