Posted on July 6th, 2021
Posted in Uncategorized
Geothermal energy is an always-on, renewable energy source that harnesses the heat energy of the earth’s interior. It made up about 0.4% of the United States’ 4 trillion kWh total electricity generation in 2020. Besides electricity generation, geothermal can be used for heating and cooling of homes. The focus of this article will be geothermal electricity production and how it may impact the oil and gas industry.
Geothermal electricity generation usually utilizes the same kinds of steam turbines as can be found in a typical coal-fired power plant. The difference is that instead of burning coal to boil water and produce steam, geothermal plants harvest the heat from within the earth to produce steam (although other working fluids can be used).
The earth has a natural geothermal gradient, and those familiar with subsurface principles probably know that gradient is nominally 1-2 °F per 100’ for on shore US oil and gas fields. Simplified, this means that the deeper a well is drilled, the hotter the rock around it will be.
In addition to a natural geothermal gradient, there are also hotspots known as geothermal reservoirs. Geothermal reservoirs are not widely distributed, and mostly occur near the boundaries between tectonic plates. Some well-known geothermal reservoirs are found in California and Iceland, which each sit on top of tectonic plate boundaries.
A number of technologies and disciplines that are already implemented day-to-day in the oil and gas industry also apply to geothermal power generation. Traditionally, geothermal power plants have been located near geothermal reservoirs since the temperatures are much hotter and the heat flux much higher than elsewhere. But developing and innovative technologies suggest if you drill deep enough and over a large enough area, geothermal power heat requirements can be met even in the absence of a geothermal reservoir.
Directional drilling, hydraulic fracturing, reservoir management, and water will be key disciplines that are involved in developing geothermal fields.
Directional drilling in combination with hydraulic fracturing will allow for development of large networks of wellbores deep underground. Hydraulic fracturing will increase the surface area of the earth that the wellbore has access to. Maximizing this surface area will be required to harvest the amount of heat required to supply the plant given the lower heat flux the earth provides in absence of a geothermal reservoir.
Reservoir management will play a role in ensuring the heat harvested from the geothermal field is in balance with the heat able to be supplied from deeper within the earth.
Water injection will be required to harvest the earth’s heat from deep below and transport it to the surface. Analogous to the water flooding of enhanced oil recovery (or solution mining of salts), water will be injected in one location, heated by the earth, and be brought to surface at the power plant where it can be used to generate steam (or vaporize another working fluid) for a turbine cycle.
Although geothermal energy only made up 0.4% of the 2020 US total electricity production, its share is expected to grow. This is because geothermal energy eliminates one of the largest challenges facing renewable energy sources such as wind (8.3%) and solar (2.3%): intermittency. The solution to wind and solar intermittency (when the wind isn’t blowing or the sun isn’t shining) is an area of active research and development for those technologies.
As each technology works to address its own challenges, the biggest drivers for the future will likely be cost effectiveness and volume of investment (typically spear headed through government subsidies). Although it is difficult to predict, it seems geothermal will be at the forefront as we in the energy industry continue to innovate to meet growing demand. At Halker, we have built a highly qualified geothermal team enabling our customers to maximize the potential of their resources.