Part 5

• Geothermal


  Geo means Earth; thermal means Heat
• Geothermal features


  • Geysers = steam jets
  • Fumaroles = vents at the surface where volcanic gases and vapours are emitted
  • Mudpots = acidic mud pool = acidic hot spring with limited water (like a bubbling mud)
• Desirable characteristics of sustainable energy supply systems


  • Renewable: non-depletable
  • Accessible and well distributed: available close to demand
  • Emissions free: no NOx, SOx, CO2, particulate matter (PM), etc.
  • Dispatchable: for base load, peak demand shaving, and distributed needs
  • Robust: Scalable:from < 1 MW to 1000 MW (thermal or electric), Flexible: generation of electricity, heat, and cogeneration
  • Reliable and safe to operate
  • Cost competitive with conventional fossil fuels
• Advantages of using Geothermal Energy to Generate Electricity


  • Clean: No emission; safe to use
  • Reliable: Continuous, reliable base power
  • Sustainable/ Reusable: Water can be recycied back into the earth and reused. No other fuel mixture required to create electricity
  • Land conservative: No major land requirement. Can be integrated into the local area without adverse effect
  • Flexible/Modular: Geothermal plants can have modular designs with additional units installed when needed to fit into growing demand of electricity
• Advantages of the Geothermal Energy Systems


  • Use of fossil fuel is limited to that needed to generate electricity to run the heat pumps
  • CO2 emissions are minimized
  • Systems require less maintenance compared to fossil-fired power generation plants on the same capacity
• Renewable Energy Sources


  • The sun --"looking outward" Examples: solar and wind
  • The earth --"looking inward" Examples: OTEC (Ocean Thermal Energy Conversion), tidal wave, geothermal
• Currently, we are 'looking outward' for clean energy technologies e.g. solar PV, solar thermal / CSP, wind
• 'Looking inward' for geothermal energy requires technology advancements and understanding of subsurface environments
• Three Methods for Geothermal Energy Capture (Heat Mining)

  • Hydrothermal
  • Deep geothermal systems hot dry rocks (HDR)
  • Geothermal heat pumps (GHP)
• Geothermal Heat Pump (Vertical Closed Loop)
• Typical Hot Dry Rocks [HDR] system Majorly for Energy conversion for end use
• Efficiency is
• Combined Heat and Power (CHP)


  Need to combine "Topping" and "Bottoming" cycles to achieve the highest possible efficiency. Combined heat and power are often produced together to maximize the use of otherwise wasted heat. Topping cycles produce electricity from high –Temperature heat, and use the waste heat for other process needs. Bottoming cycles use medium-Temperature heat to generate electricity.
• Aquifer


  An underground layer of water bearing permeable rock, rock fractures, or unconsolidated materials. Groundwater from an aquifer can be extracted through a well. It is also a body of porous rock or sediment saturated with ground water.
• Twin Borehole System for Heat Extraction from an Aquifer

  1. Cold water is injected at the inlet borehole x = 0

  2. Hot water is extracted at the outlet borehole x = L

  3. Assume that the aquifer is initially at temperature T1

  4. The cold water at inlet is at temperature T0
• Darcy's law for fluid flow through a porous media

  • In order to obtain a given volume flow rate Q, it is necessary to apply a pressure drop P between the boreholes
  • The volume flow rate Q through a slab of porous rock of cross-sectional area A and length L, is given by Q = (k*A*P)/L, where k is the permeability
• Lost Drilling Circulation Mud Increases Costs
• Need to detect and mitigate the problem of drilling mud being lost/leaked into the rock formations during drilling


  • Early detection of lost circulation mud is crucial in minimizing problems
  • Risk mitigation includes development of a rolling float meter for mud outflow and an advanced, acoustic Doppler flow meter for mud inflow to detect and quantify lost circulation
  • Work is also being done to integrate the rolling float meter into an expert system that will diagnose drilling problems and recommend action
• Slimhole Drilling


  • Use of smaller-than-standard-diameter drilling bits and pipe to reduce oil and gas exploration costs by 25 to 75%
  • Need to investigate whether slimhole drilling can provide sufficient data to characterize a geothermal reservoir and how slimhole-drilling costs compare with conventional-sized holes
• Diagnostics-While-Drilling (DWD)


  A concept that uses a closed information loop carrying data up and control signals down between the drilling platform at the surface and tools at the bottom of the hole
• Faster drilling and problem mitigation are clearly important for reduced cost, but truly cost-effective drilling also requires that all functions of the overall process operate optimally
• The graph shows the "upward and downward" high-speed information flow to diagnose the drilling conditions in real time
• Variation of Temperature with Depth Across Three Zones of Differing Thermal Conductivity (KT)