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GEOFAR : Innovative geothermal technologiesLast modifications: 2009-10-14

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GEOPRESSURIZED SYSTEMS

GENERAL PRESENTATION

Context

Geopressured resources are deep reservoirs of high-pressured hot water that contain dissolved natural gas. A

geopressured reservoir is formed in sedimentary formations when water percolates into the pores of a layer of

sand. When non-porous shale settles on top, it traps the fluid into the sand layer at very high pressures. Over

millions of years, this pressure increases even more as additional sedimentary layers build on top of the reservoir.

If the sand body in which the water is trapped is large enough, the reservoir can economically produce energy for

quite a long time. An important characteristic of geopressured reservoirs, at least from an energy perspective, is

that they contain dissolved methane, or natural gas. This, therefore, yields three sources of energy that can be

utilized from the reservoir:

1. Hydraulic energy from extreme pressure

2. Heat energy from the fluid

3. Dissolved natural gas

Comparing to other natural gas reservoirs, the amount of dissolved methane in these types of reservoirs is very

small. For the natural gas alone, the reservoir would be uneconomical. However, with two more sources of

energy, their utilization becomes worthwhile.

A geopressured geothermal facility operates on both natural gas and geothermal fuel. It could also be considered

as a geothermal-fossil fuel hybrid system.

State of the art

A successful demonstration plant operated in US in the 1980’s. The Department of Energy built a demonstration

plant in Texas which produced electricity from geopressured resources. Although it run successfully as a

demonstration, it was not considered economic at the time and was dismantled by the US Department of Energy.

Geothermal solution

In the USA, there is a renewed interest in the energy potential of geopressured geothermal resources. Congress

authorized new technology demonstrations for geopressured geothermal systems in 2007.

Resources of this type exist in the North Sea and can be found in deep ponds in Europe.

FOCUSING ON THE GEOTHERMAL SOLUTION

Current status of the solution

Comments

Scientific Project (only on paper or

under preparation)

Demonstration project One demonstration project was built in the 1980’s. Nowadays new

interests are appearing and another demonstration project is


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currently developed in the USA.

Scientific Pilot

Industrial Pilot

Industrial stage

Other?

Advantages

(1, 2, 3, 4

or 5) *

Comments

Environmental

Economical 4 Multi uses of the resources extracted from one well

Social

ScientificallyOthers

* 1(very few advantageous) to 5(totally advantageous)

Advantages against other applications

For the natural gas alone, the reservoir would be uneconomical. However, with two more sources of energy

(including geothermal heat), their utilization becomes worthwhile.

Focusing on Economic Feasibility

- Estimated costsIt is impossible to make generalities about the costs due to the character of the project.

- Impact on profitability

Geopressured geothermal resources have not been tapped since they were successfully demonstrated almost

two decades ago, when oil and gas costs were low. Today’s increasing oil and gas costs make the economics of

geopressured applications look particularly promising.

However, American researchers argue that a fresh approach to geopressured resources is called for. Advanced

technology, coupled with greater need for domestic energy and higher values for both electricity and natural gas,

could result in economical production from the substantial geopressured resource base.

EXAMPLES/CASE STUDIES

Location

Demonstration Project: Pleasant Bayou (Texas, USA)

Technical characteristics of the operation

The US Department of Energy embarked on a project to demonstrate geothermal geopressured resources in the

1980s at Pleasant Bayou in Texas. The original concept as defined in the DOE document was to tap into three


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forms of energy: heat from the geothermal resource (thermal energy), energy from natural gas in the reservoir

(chemical energy), and well head pressure (mechanical energy). Due to cost considerations, in the Pleasant

Bayou demonstration plant only the thermal and chemical energy were captured. Exhaust heat generated from

the onsite burning of the natural gas was recovered to improve cycle efficiency. The one megawatt geothermalgeopressured project was tested in October through December 1989. The demonstration ran January through

May of 1990. The design power plant output was 905 kW, with slightly over half of the power derived from the gas

engine. Though the capacity factor was decreased due to a 3-day plant outage and a 4-week turbine outage, the

overall plant availability was 97.5 percent. During the 121 days of operation, 3,445 MWh of electricity were sold to

Houston Power and Light.

According to experts associated with the project, there were no major technical problems—carbon deposits

accumulated in the exhaust gas heat exchanger, but these were easily removed. Scale inhibitors were used

successfully to control scale in the production well at the facility.

SOURCES AND CONTACTS

http://www.geo-energy.org/publications/reports.asp

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