Enhanced geothermal systems

In geothermal reservoirs the energy is extracted from the underground/subsurface reservoir by circulating water (cold water is injected and hot water is pumped) through fractures/joints in a relatively impermeable reservoir. The heat extraction process depends on coupled thermal, hydraulic, mechanical and chemical (THMC) properties of fractured rock formations. Thus the heat extraction/production involves multiple processes: convection (within the heated fluids), advection (transport of heat, and reactants products by bulk motions of fluids), heat conduction in the rock, molecular diffusion, hydrodynamic dispersion and thermo-poro-elastic deformation of rock

1. Coupled thermo-hydro-mechanical (T-H-M) modeling

Hot water extraction and cold water injection into an underground geothermal reservoir cause mechanical deformation of rock matrix and rock joints/fractures. That leads to alteration of hydraulic transmissivity. Link

The spatio-temporal variations of fracture aperture greatly impacted the thermal drawdown and consequently the net energy output. Link

2. Coupled thermo-hydro-chemical (T-H-C)

Heat extraction by cold water circulation disturbs the thermo-chemical equilibrium of a geothermal reservoir, activating the dissolution/precipitation of minerals in the fractures. Link

Heterogeneous aperture distribution is very common in large faults or fracture connecting injection and production wells. The formation of a preferential flow path or channel is one of the most important consequences of heterogeneity when aperture alteration due to thermo-chemical and thermo-mechanical effects is significant. Link

For injection of undersaturated or oversaturated water with respect to the solubility of amorphous silica, the highest rates of reactive alteration occur at some distance away from the injection well. This is largely because the temperature dependence of the reaction rate plays a much greater role than temperature dependent solubility. For oversaturated injection, precipitation occurs in a band, confining the flow system to smaller areas. For undersaturated injection, dissolution causes permeability growth far from the injection well, resulting in longer flowpaths that prevent short-circuits, which implies favorable conditions for sustained energy production. Initial permeability heterogeneity influences reservoir response significantly only when the correlation lengths are of the order of 1/10th of the fracture size or more. Link

3. Coupled thermo-hydro-mechanical-chemical (T-H-M-C)

Long-term permeability change during geothermal heat extraction is influenced by complex interactions among fluid flow, reaction rates, mineralogy, thermo-mechanical properties of reservoir, residence time of fluid, joint stiffness and heterogeneity. Link

4. Machine learning to predict the thermal drawdown

Machine learning techniques are computationally inexpensive compared with experimental and numerical approaches. Link

5. Heat extraction from fault dominated heterogeneous geothermal reservoir

6. Heat Extraction from depilated oil/gas reservoir and hybrid solar-geothermal system

7. Experimental enhanced geothermal systems

Geomaterial composed of a wide range of minerals such as albite, quartz, calcite, dolomite, feldspar, plagioclase, siderite, and pyrite. The mineralogical heterogeneity and interconnectivity of minerals leads to complex porestructures, due to the vast range of pore sizes.

8. Brittle mechanics

9. Discrete Element Modeling

10. Non-destructive testing

11. Four Dimensional X-ray Microscopy (FDXM)

12. Field Emission Scanning Electron Microscope (FESEM)

13. Energy Dispersive X-Ray Spectroscopy

14. Geothermal energy potential in India

India has significant amount of geothermal energy stored under its large land mass. The geothermal resources in India are basically of low and medium enthalpy. The available resources can be utilized for direct use and generating electric power. In India, around 400 thermal springs with heat flow (78-468 MW/m2) and thermal gradient (47- 100 oC/km) were traced by the Geological Survey of India (GSI) over past three decades. The investigation shows some provinces are highly suitable for the electricity generation. Geological Survey of India also estimated the potential of generating electricity as in the order of 10 GW. For direct use the map prepared by GSI indicates power production in the order of 1000 GWt . For the time being the available resources are of very little use for direct applications (265MW installed for bathing/swimming with an annual use of 2545 TJ). Geothermal provinces of India