Geological Thermal Energy Storage (GeoTES): Combined with Concentrated Solar or Heat Pumps: Premier Resource Management’s GeoTES Project in California and Potentially Other Areas in the Southwest U.S.

 

     California company Premier Resource Management expected to drill and operate oil wells when they bought wells and leases in California’s Central Valley in 2018. This area in Kern County near Bakersfield is one of California’s largest legacy oil fields. They could not get permits to drill due to California’s regulatory environment which tends to be hostile to fossil fuel producers. Instead, beginning in 2020, they are focusing on geological thermal energy storage (GeoTES). This means utilizing favorable geology to store geothermal energy in the form of pre-heated water that is injected through one well and produced through another well when needed to power steam turbines to produce electricity.  Geological favorability also includes a reservoir temperature that will keep the water hot. Areas where the geothermal gradient, or temperature increase with depth, is higher than normal, are most amenable to geothermal energy storage. The company thinks that they can store the water in a usable state, heated at the surface with solar collectors utilizing parabolic mirrors to concentrate the energy enough to heat the water, for a month or more. They plan to use the brackish water already in the reservoirs. They plan to pump it to the surface, then heat it to 700 degrees F, run it through heat exchangers, and then inject it back underground. This project involves drilling new geothermal wells, but other projects may utilize existing wells.

     The company is partnering with the National Renewable Energy Laboratory (NREL), Berkeley National Lab, Idaho National Lab, and industry partner Ramsgate Engineering. This first pilot is still in the planning and permitting stage. It is hoped that the demonstration plant will begin construction in 2026 or 2027. NREL is also working with a company in Texas to store energy in existing wells, but in reservoirs that have not produced hydrocarbons, perhaps in deep saline aquifers, but maybe in shallow freshwater or brackish water aquifers as well.

     Geological thermal energy storage utilizing existing oil and gas wells being combined with solar heating requires certain conditions to be most successful and economical: adequate sun, suitable geology, distance from homes or sensitive areas where water contamination could be an issue, and proximity to power transmission lines.

     Premier’s CEO Mike Umbro thinks that eventually, California’s San Joachin Valley alone can support 60 GW of GeoTES. He noted some other advantages such as the project uses existing oilfield land with no new land disturbed and the components of the system will all be low to the ground and so less of an eyesore than oilfield equipment. They also tout jobs. They think their project will support 200-400 construction jobs lasting 10 years or more and 100 ongoing jobs. According to a 2023 report the pilot demo project is expected to produce 10 MW of electrical power for five hours every night. According to the same article in ThinkGeoEnergy:

 

“The company is planning to construct 60-acre solar arrays and a series of tanks for separating and cleaning the water. Energy will be stored in 37 geothermal wells. The system would then be connected to a nearby substation and power transmission lines owned by Pacific Gas and Electric Co.”

    

Umbro stated then:

“We believe the oil fields could meet roughly half California’s 2045 long duration energy storage goals — with 45 gigawatts of potential on the west side (of Kern) alone.”

     If the pilot project works as designed the company plans to expand the project to 400MW of energy storage at a cost of about $2 billion. A project that size could power Bakersfield as needed. GeoTES provides long-duration energy storage that can provide needed support for seasonal low output of solar in the winter. When this happens California turns to natural gas. As a state, California is one of the biggest consumers of natural gas. Gas is especially needed on hot summer days and in general through the winter. Winter natural gas price spikes are common. Such systems could mitigate these issues. Of course, the potential avoided carbon emissions are desirable as well and should help to speed up permitting, although that does not seem likely.

Schematic of Premier Resource Management's Project

     NREL describes the project as follows in terms of its components: reservoir circulation, solar heat collection, and power generation:

Reservoir Circulation:  The project will be equipped with multiple producing and injecting wells in a “seven-spot” arrangement.  Seven spots typically possess improved reservoir contact and increased lifting capacity where reduced, flow-related pressure drop in the reservoir is desired, when compared to five-spot geometry.  The reservoir circulation loop will operate with varying circulation rates depending on demands made by the two other, interacting loops.

Solar Heat Collection:  Solar heat will be collected using helio-dynamic, parabolic trough-style solar concentrators.  Heat will be absorbed into a circulating working fluid, it being heated to roughly 700F.  As heat is collected this loop will command the Reservoir Circulation loop to provide sufficient fluids to absorb the collected solar heat.

Power Generation:  The Reservoir Circulation loop will provide heated fluids sufficient to boil and superheat a power-producing working fluid, which will be circulated through a power turbine.  When power is demanded by the power grid this loop will command the Reservoir Circulation loop to deliver sufficient heat for power production purposes.

The pilot project will consist of seven, 2½ acre seven spot patterns.  Roughly 40 acres of solar collectors will be installed to support the process heating requirement and a 10MW peaking turbine/generator will be installed to generate pilot project sales-power.

Cost estimates and a timeline for the project is shown below:

Source: NREL

 

Different Configurations of Geological Thermal Energy Storage Being Explored by NREL and Others

     The above project utilizes concentrated solar to heat the water. The other main way to heat the water is via a heat pump system which uses electricity. This is known as a Carnot Battery. The heat can be used for industrial processes as well. NREL compares costs, as levelized cost of storage (LCOS), for GeoTES vs. other types of energy storage:

 “… a GeoTES charged with solar thermal energy and calculated it to have a levelized cost of storage (LCOS) of 0.12 $/kWhe for 700 hours of capacity. This value was low compared to other comparable technologies at the same scale, such as hydrogen (0.5 $/kWhe), compressed air energy storage (2.8 $/kWhe), and pumped hydro-electric storage (1.6 $/kWhe) (Sharan et al., 2020). These low costs derive from the fact that – unlike other storage systems – the GeoTES storage volume has little-to-no cost. Wells provide access to the reservoir and determine the rate that energy can be extracted (and therefore the cost of power), but the marginal cost of adding energy capacity is effectively zero as long as the reservoir volume is large enough.”

This analysis suggests that GeoTES will be quite competitive with existing long-duration energy storage, including pumped hydro, by far the most common form of it. GeoTES can be used to provide an array of energy storage services including “load-shifting, arbitrage, grid reliability, energy capacity, and seasonal storage.”

     Systems heated with concentrated solar thermal (CST) utilize a parabolic trough collector (PTC) system where the mirrors concentrate the solar energy, and a piping system utilizes mineral oil as a working fluid in the heat exchange system.

Source: NREL

     Carnot batteries use heat pumps. There are a wide range of working fluids and configurations that have been explored, including different power cycles and thermal storage materials. Carnot batteries typically use thermal energy stored at the surface in tanks of water, molten salt, or fluidized particles. GeoTES Carnot batteries use the heat underground to insulate the fluid to keep it warmer longer. Heat can also be utilized for heating and cooling through exchangers. The cost for this heat as a levelized cost of heat (LCOH) is comparable to the price of natural gas. Working fluids such as supercritical CO2 (sCO2) can be among the most efficient.

Source: NREL

The results for a concentrated solar (CST) system and a Carnot Battery (CB) system are shown below:

Source: NREL

     NREL came up with a techno-economic model for GeoTES heated with concentrated solar or heat pumps utilizing depleted oil & gas reservoirs or suitable shallow reservoirs. Like in enhanced geothermal systems, these reservoirs may be naturally porous or fractured, may have been previously hydraulically fractured, or may be hydraulically fractured within the scope of the project. Adequate permeability, typically fracture permeability, is required to get the needed flow rates. Suitable geology also includes an adequate seal both above and below the reservoir to keep fluids contained, an aquifer that is reasonably confined. NREL notes that while upfront costs can be high for GeoTES, the levelized cost of storage is much lower than both molten salt and battery storage as the following graph shows.  

 

Source: NREL

NREL also shows a single well configuration with a hot well and a cold well. With this configuration, the hot well is the only well charging and discharging the system. The cold well keeps the reservoir adequately pressured and keeps the supply going to the heat exchanger.

Source: NREL

 

NREL also describes the main geological suitability requirements:

 

1)        Reservoir temperature – a minimum temperature of 91 deg C (195 deg F) is required for binary systems. Higher temps increase the efficiency of power cycles.  

2)        Reservoir pressure – a depleted reservoir is often a pressure-depleted reservoir, which means that the current reservoir pressure is much less than the original pressure. In this case the reservoir needs to be re-pressured so that it can reestablish geopressured where the reservoir pressure exceeds the hydrostatic pressure and the fluid will naturally flow to the surface when given a borehole.

3)        Porosity and permeability of the formation – as mentioned this is all about getting adequate flow rates in geothermal and GeoTES. These properties vary considerably among different rock formations and fluid reservoirs.

4)        Potential for scaling and clogging – this too is a risk for both geothermal and GeoTES wells. Properties like pH, formation water composition, mineralogy, temperature, pressure, injection rates, and presence of salt, affect scaling and clogging likelihood.

5)        “Permeability of caprock/seal: Low permeability seals/caprocks act as a barrier for heat and mass flow and also stops inflow and outflow of gasses such as methane, CO2, and sulphur oxides.”

6)        Presence of oil remaining – this can be beneficial as an enhanced oil recovery operation could be done simultaneously, adding to project revenue. I would expect more pilots to utilize a hybrid system like this.

7)        Formation depth – it costs more to drill deeper, but temperature increases with depth so both costs and benefits change with depth.

8)        Formation damage from geothermal extraction -  changes in reservoir temperature after prolonged production and injection can result in the plugging of clay particles, reducing permeability.

9)        Steeply dipping beds in the formation – this can cause updip movement of hot water away from production wells due to buoyancy.

 

 

References:

These abandoned oil wells near Bakersfield could store enough solar power for 300,000 homes. Adele Peters. Fast Company. June 7, 2024. These abandoned oil wells near Bakersfield could store enough solar power for 300,000 homes (msn.com)

Geological Thermal Energy Storage Using Solar Thermal and Carnot Batteries: Techno-Economic Analysis. Preprint. Joshua D. McTigue, Guangdong Zhu, Dayo Akindipe, and Daniel Wendt. NREL. 87000.pdf (nrel.gov)

Techno-Economic Analysis and Market Potential of Geological Thermal Energy Storage (GeoTES) Charged With Solar Thermal and Heat Pumps into Depleted Oil/Gas Reservoirs and Shallow Reservoirs: A Technology Overview. Preprint. Guangdong Zhu, Dayo Akindipe, Joshua McTigue, Erik Witter, Trevor Atkinson, Travis McLing, Ram Kumar, Pat Dobson, Mike Umbro, Jim Lederhos, and Derek Adams. NREL. September 2023. https://www.nrel.gov/docs/fy23osti/86609.pdf

Premier Resource Management LLC is working on a hybrid solar power and geothermal energy storage project in Antelope Hills in Kern, California. Carlo Cariaga. ThinkGeoEnergy.  June 5, 2023. Geothermal energy storage project proposed in Kern County, California (thinkgeoenergy.com)