Steam-based geothermal systems have been well-studied and developed since the first small successes in Lardarello in 1911.  However, geothermal steam for direct power generation is a rarity around the world, and extremely site-specific.  The Iceland successes are well-known, as are fields such as Cerro Prieto and the Geysers, but >98% of the land mass of the world does not have High-T (steam) systems.  Thus, we will focus on medium and low-grade systems in permeable reservoirs, and in hot dry rock at depth.

We will also discuss geothermal energy storage, geothermal fluids, HDR stimulation, and related topics.  Our intent is to leave you with a broad understanding of the thermal energy beneath our feet, how we might exploit it, and how we might even store heat in a “Thermal Battery” for power generation, or for habitat heating.  Geothermal energy may fit comfortably with renewable energy sources (hydro, wind, sun) but integrating different combustion-free energy sources required careful planning and good geological and mechanical engineering.    

1.     Introduction

a.     Geothermal systems (petroleum system elements format)

 i.     High-T Steam systems – dry steam, wet steam

 ii.     SedHeat systems – hot aqueous fluids in porous permeable strata

 iii.     HDR systems – Hot (& warm) Dry Rock systems with minimal permeability

b.     Low energy, high energy systems

 i.     Lowest energy systems are geothermal gradient systems

 ii.     Highest energy systems are supercritical water systems at moderate depth

 iii.     Intermediate energy systems in hot areas of sedimentary basins

c.      Temperate and Northern climates

 i.     Extreme need for heat in sub-arctic and artic climate zones

 ii.     Use of heat for power, habitats, agriculture

d.     Tropical and Arid Environments

 i.     Extreme need for cooling in hot-dry and hot-humid climates

 ii.     Combining geothermal and other renewable energy sources for cooling

2.     Clastic Reservoirs

a.     Typical petrophysical properties (e.g. geopressured aquifers in the GOM)

b.     Adequate flow and energy flux

3.     Carbonate Reservoirs (Volker)

a.     Carbonate systems, naturally fractured strata (dual porosity systems)

b.     Hot fluids from oil production

4.     HDR – Hot Dry Rock

a.     EGS – Enhanced Geothermal Systems

b.     Naturally fractured systems and stimulation

c.      Advective and conductive heat flux

5.     Saline Aquifers and Salt

6.     Data collection and requirements

a.     Thermal information: T (z, t…), specific heats, porosities, thermal conductivities, etc.

b.     Fluid flux information: reservoir characteristics, well stimulation effects

c.      Geochemistry of fluids and scale potential in SedHeat and High-T systems

d.     Microseismic surveillance, Deformation monitoring, Pressures … 

7.     Geotechnical Constraints and Hazards

a.     Fluids management

b.     Hydraulic fracture stimulation

c.      Induced seismicity – ΔT, Δp effects

8.     Energy Storage

a.     Heat storage in shallow geo-repositories (<1000 m)

b.     Heat storage in deep geothermal heat reservoirs

c.      Integrating geothermal energy with compressed air energy storage