This generation has the great honor to transition from the Fossil Fuel Age to renewable resources. During this development, it would be fruitful to reuse oil and gas wells as geothermal energy plants.
Adaptive reuse of society's legacy from previous economic regimes can lead to low-cost and highly sustainable future. No one knows exactly how many oil and natural gas wells there are in the world, but the value is in the tens of millions.
The geothermal activity varies from well to well depending upon factors such as well depth, the thickness of the Earth's crust in that area, and local subterranean temperature. Many of these wells were drilled deep into the earths crust, even as far as 11 km deep.
While a well with a temperature of 200°C can power a city, even wells which produce 37°C can power a neighborhood. Several smaller wells in close proximity can also be combined into one system.
An oil or gas well does not have to be empty to harness geothermal energy: even operating wells can use the heat of rising water or petroleum for geothermal power. In the case of depleted wells, often hot water can be brought to the surface. If a well is hot dry rock, Enhanced Geothermal Systems can be used.
Texas is leading the way towards capturing geothermal power from active and empty oil wells ("Stripper fields" is the Texas lingo for depleted oil and gas wells) of which the state has over 1,000,000. Building off abundant existing oil and gas infrastructure, several transformation studies have been completed with promising results. They have shown that existing oil and gas wells posses temperatures within the range for electrical power production [pdf].
"There are 5,000 megawatts of geothermal power in hot water coming up from abandoned oil wells in West Texas," says Karl Gawell, executive director of the Geothermal Energy Association, a trade consortium. "All that energy is just being wasted." [link]
Geothermal energy provides clean, renewable baseload electricity available 24 hours a day, seven days a week, unlike the inherent uncertainty with wind or solar energy. Geothermal heat as low as 37°C can be used to make electricity in a binary power plant. This method of power generation is very environmentally-friends as binary plants use a self-contained cycle. Nothing from the process is emitted, including "greenhouse gases".
To take advantage of the Fossile Fuel Age's legacy resources, oil and gas wells throughout the world should be evaluated for their geothermal potential. However, I would like to offer a further consideration.
Cities in the temperate regions of the earth not only have a high demand for electricity, but also heat. Geothermal wells cogenerate electricity and heat. In order to effectively use the heat resource, which has a low transmission distance, future communities could be stragetically located on post-oil well sites. Heat accounts for a large percentage of building upkeep costs. It has already been shown that cascading heat from natural resources and industry in places like Denmark and Iceland works.
The energy (and exergy) from the well would then be used several times. Heat would cascade from power generation, to heavy industry, to greenhouses, and finally to dwellings, which only require 40*C.
The vision is for a city which blooms around the geothermal hotspot as desert life is centered around an oasis.