Geothermal engineering

The Greek words gê, which means Earth, and thérm, which means heat, are combined to form the word "geothermal".  Geothermal energy is the thermal energy that the Earth produces. Geothermal resources refer to localized areas inside the Earth's crust that contain significant amounts of heat energy. Geothermal energy, or heat, that is currently or reasonably soon obtainable and economically used

There are thermal energy concentrations close to the Earth's surface that can be exploited as an energy source because of spatial fluctuations in the thermal energy found in the planet's deep crust and mantle. Three main mechanisms—conduction through rocks, magma rising to the surface, and deep water circulation—transmit heat from the Earth's lower layers. Most high-temperature geothermal resources are linked to heat concentrations that happen when magma (melted rock) moves to places close to the surface, where it can store heat. Due to the low heat conductivity of rocks, massive magma intrusions may take millions of years to cool.

Geologic mapping, geochemical analysis of water from hot springs, and geophysical techniques utilized in the mining sector are the most prevalent methods employed in the exploration for geothermal resources. With developments in seismic methods, reflection seismic surveys are increasingly being employed. Geothermal drilling relies on technologies used in the oil/gas sector that are updated for high temperature applications and wider well sizes. Because high flow rates are often required for profitable production, the oil and gas industry has developed methodologies for extensively fractured reservoirs that are used in well testing and reservoir engineering.

Types of Geothermal Systems

Exploitable geothermal resources are hydrothermal systems containing water in pores and fractures with sufficient permeability to produce fluids in adequate volume. Most hydrothermal resources contain liquid water, but higher temperatures or lower pressures can create conditions where steam and water, or steam alone, are the continuous phases. Examples of steam-alone fields are among the oldest developed geothermal fields—Larderello in Italy and The Geysers in Northern California. These types of geothermal fields are termed "vapor-dominated" because the initial pressure follows a vapor-static gradient, as opposed to hydrostatic gradients in liquid-dominated fields.

Other types of geothermal systems that have been looked into for energy production are (1) geopressured-geothermal systems, which have water that is slightly warmer than normal and under a lot more pressure than hydrostatic for its depth; (2) magmatic systems, which have temperatures between 600 and 1,400 °C; and (3) hot dry rock (HDR) geothermal systems, which have temperatures between 200 and 350 °C. HDR systems are characterized, as are subsurface zones, with low natural permeability and little water. Currently, only hydrothermal systems shallower than about 3 km and containing sufficient water and high natural permeability are exploited.

A more recent addition is "enhanced geothermal systems" (EGS), which fall between HDR and hydrothermal systems. These may lack enough fluid or have low permeability for commercial use, and ongoing research focuses on injecting fluids and enhancing permeability for improved efficiency. Currently, only hydrothermal systems less than 3 km deep with sufficient water and high natural permeability are actively utilized for energy production. Another option is utilizing the heat from beneath the Earth's surface with low hydraulic conductivity, occasionally termed deep heat mining (DHM). Given that the continental crust is primarily composed of granite or gneiss, HDR systems specifically target granitic heat reservoirs. HDR systems typically aim for temperatures above 200 °C, requiring the drilling of wellbores reaching depths of 6 to 10 km in the continental crust, which maintains an average geothermal gradient.

Geothermal Energy Potential

Estimates of potential for geothermal power generation and thermal energy used for direct applications are available for most areas. The most recent review of worldwide electrical generation reports 12,810 MW_e (megawatts electric) of generating capacity is online in 23 countries (Table 9.1). Since that report, additional 4,013 kW_e capacity has been added in Indonesia, the most additional capacity of all countries. The expected capacity in 2005 is 19,757 MW_e. Geothermal resources also provide energy for agricultural uses, heating, industrial uses, and bathing. Fifty-five countries have a total of 16,209 MW_t (megawatts thermal) of direct-use capacity. The total energy used is estimated to be 45,000 TW-hrs/yr (terawatt-hours per year).

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  Table 9.1—Worldwide Installed Geothermal Electrical Generating Capacity in 2016 in Megawatts Electric(MWe)

Gawell et al. estimate that identified geothermal resources using today's technology have the potential for between 35,000 and 73,000 MW of electrical generation capacity. The Gawell study relied on expert opinions and generally focused on identified resources. Stefansson prepared an estimate of identified and unidentified worldwide potential based on the active volcanoes of the world. He estimates a resource of about 11,200 ± 1,300 TW-hrs/yr using conventional technology and 22,400 using conventional and binary technology (Table 9.2). Stefansson points out that his estimate is in general agreement with that of Gawell et al., although individual regions may not be in agreement.

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  Table 9.2—Estimated Geothermal Resources Suitable for Electrical Generation Reported as Terra-Watt Hours per Year (TWH/A)

The U.S. Geological Survey has prepared several assessments of the geothermal resources of the United States. Muffler estimated that the identified hydrothermal resource, that part of the identified accessible base that could be extracted and used at some reasonable future time, is 23,000 MW_e for 30 years. That is, this resource would operate power plants with an aggregate capacity of 23,000 MW_e for 30 years. The U.S. undiscovered resource (inferred from knowledge of Earth science) is estimated to be 95,000 to 150,000 MW_e for 30 years.

Muffler also provides an explanation of the terminology used to define the various categories of resources. Resource base is all of the thermal energy contained in the Earth. The portion of the resource base that is accessible is shallow enough for production drilling to reach it. Resources are those portions of the accessible base that can be used at some reasonable future time. Reserves are that portion of the resource that has been identified and can be used under current economic conditions. Resources are also divided into categories of "identified" and "undiscovered," based on knowledge of the certainty of their existence.

Geothermal Exploration

Geochemical Studies

Geophysical Techniques

Geophysical Methods in Geothermal Exploration and Field Operations

Geothermal Drilling

Background

Nature of Geothermal Formations

The Key Differences between Drilling Operations in Geothermal and Oil and Gas

Well Design in Geothermal

Well Type

Comparison Parameters of Various Well Type

Casing Design in Geothermal

Cementation of Casings in Geothermal

Drilling Fluids in Geothermal

Well Control in Geothermal

Geothermal Drilling Technology

Drill Pipe Continuous Circulation Device (CCD)

Drilling with Casing (DWC)

Reservoir Engineering

Definition

The Development of Geothermal Reservoir Engineering

Reservoir Characterization

Well Testing

Completion Test

Injectivity Test

Heating Measurement

Production test

Transient Test

Partial Penetration

Decline Curve Analysis

Data Preparation: Normalizing Flow Rates

Arps Decline Curves

Fetkovich Type Curves

Tracer Testing

Geothermal Tracers

Recent Advancements in Tracer Technology

Tracer Selection Criteria

Injection and Sampling Techniques

Analytical Modeling Methods

Interpretation Methods

Flow Channel Model

Advancements in Quantitative Analysis Techniques

Interpreting Tracer Data in Heterogeneous Reservoirs

Numerical Simulation

The Evolution of Geothermal Simulation

Challenges in Modeling Geothermal Reservoirs

Governing Equations

Conceptual Models and the Native State

The Impact of Fractures

The Simulation Process

Future Directions

Field Operations

Stimulating Production

Measurements in Geothermal Production Applications

Mass Flow

Flow Measurement Errors in Well Testing

Fluid Compositions

Geothermal Energy Conversion Systems for the Production of Electrical Power

Direct Steam Systems/Vapor-Dominated Resources

Flash Steam Systems/Liquid-Dominated Resources

Binary Systems/Liquid-Dominated Resources

Nomenclature

Acknowledgments

Copyright Notice

Noteworthy papers in OnePetro

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External links

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See also

PEH:Geothermal Engineering