Session 1D: Energy Conversion/Utilization

Flexible energy resources are key for a reliable power supply in a decarbonized grid with a significant fraction of variable power sources. Geothermal energy has always been an economic resource for baseload power and district heating. Recently, geothermal facilities have been expanding beyond baseload to supply flexible heat and electricity. Geothermal Energy can be harnessed through Enhanced Geothermal Systems (EGS). EGS involves creating an artificial reservoir by stimulating the natural permeability of hot rock formations beneath the Earth's surface. However, EGS may result in fast thermal depletion due to continuous fluid circulation. To slow down EGS thermal depletion due to continuous fluid circulation, we proposed the Huff &Puff technique as a better system, providing increased contact time between the injected working fluid and the hot geothermal rocks. The primary objective of this work is to determine the technical and economic feasibility of harnessing geothermal energy from deep Enhanced Geothermal Systems using the huff-and-puff approach. We also aim to determine the optimum injection, soaking, and production schedule. In addition, we also determine the optimum fracturing and post-fracturing production period by analyzing the fracture propagation distance. To carry out these investigations, we use a 3-dimensional coupled thermo hydro mechanical numerical model to understand the system performance and the effect of different parameters on energy production. The outputs considered are wellhead temperature and production mass flow rates. We then use a tool called FGEM, Flexible Geothermal Economics Modeling, which is specifically designed for the techno-economic analysis of flexible geothermal power generation. We apply this flexible geothermal economics modeling to optimize EGS huff-n-puff systems.

Geothermal production wells are susceptible to pressure decline over time, which could make them unusable for power generation when their pressure drops below the plant's operating conditions. This situation could decrease the power output, necessitating drilling make-up wells at a considerable capital cost. This study looks at options for using an ejector to mitigate this problem. An ejector is a static device that can potentially be used to draw fluid from a low-pressure well using a flow from a nearby high-pressure well. In ejectors, two flows are combined in a mixing chamber, and the mixture passed through a diffuser, leaving at an intermediate outlet pressure, which could be higher than the pressure of the low-pressure well.

Although ejectors are widely utilized in industries such as oil and gas and refrigeration, their application in geothermal energy has mainly been limited to gas extraction from power plant condensers. However, the literature lacks reports of successful ejector use for inducing geothermal fluid from low-pressure wells. As part of the Geoejector project, this paper focuses on the design, development, and performance analysis of a supersonic laboratory scale ejector prototype constructed at Reykjavik University. The prototype was tested using saturated steam for primary and secondary flows under different pressure conditions.

A new supercritical carbon dioxide (sCO2) turbine has been tested to conditions anticipated for geothermal power production. The prototype machine owned by Sage Geosystems was designed by Southwest Research Institute for operation in a low to mid-enthalpy geothermal field at a 3MW scale. The closed loop CO2 system within the plant will allow for improved conversion of heat to power by taking full advantage of the efficiency and power density of sCO2 turbomachinery. The megawatt scale system offers a significant reduction in overall size vs other commercial systems.

This paper will present data from the laboratory testing at SwRI to show aerodynamic performance and power output along with how the information is used to prove the models of the 3MW setup under field conditions. The proven mechanical integrity and rotordynamics of the modular design will also be discussed along with feedback of turbine subsystems used for this design.

The turbine testing has shown great results during operation with CO2 at mid-enthalpy temperatures (150-250°C). The paper will conclude with details on the turbine startup and shutdown process to provide a better understanding of potential use cases for a similar class turbine.

The combined utilization of Organic Rankine Cycle (ORC) technology and advancements in enhanced geothermal systems (EGS) hold significant promise for unlocking the full potential of geothermal resources for dispatchable power generation. Geothermal energy, with its inherent reliability and minimal carbon footprint, presents a compelling solution for sustainable electricity production. Modern drilling techniques and subsurface analytics complement ORC systems, creating a synergistic partnership that addresses key challenges in future grid management.

Future grids require firm, clean, dispatchable power to ensure reliability and sustainability. To examine this need, we took data from NREL's Cambium mid-case scenario, identified the highest emission hours per month in 2035, and then averaged net load and emissions by hour for that month. This approach allows us to pinpoint the periods within the year when emissions are at their peak, offering insights into the correlation between net load and emissions during these critical hours. The results highlight the necessity for energy resources that can ramp up production quickly and efficiently, particularly during non-solar hours. We then discuss how EGS and ORC systems enable the extraction of continuous, dispatchable, carbon-free power from geothermal resources, contributing to a more sustainable and resilient energy mix.

High Temperature Reservoir Thermal Energy Storage (HT-RTES) is a promising solution for large-scale energy storage that can stabilize the electric grid, increase its flexibility, and provide energy on demand. Despite its advantages, the HT-RTES wells require a higher standard for cement integrity due to higher temperatures and thermo-mechanical stresses during injection and production. In this study, we provided a thorough mechanical investigation on the hydrophobic fly ash cenospheres (FCS) incorporated calcium aluminate cement, which exhibits a lower thermal conductivity compared to conventional oil and gas well cement to prevent heat losses. The cement was treated with superhydrophobic polymethylhydrosiloxane (PMHS). The compression tests were conducted under in situ high pressure high temperatures, with pressure reaching up to 10 MPa and temperature up to 180 °C. The findings revealed that the PMHS-treated specimens, after undergoing simulated thermo-mechanical stresses, showed an increase in cement compressive strength from 4.6-30 MPa to 6.1-33 MPa, an improvement in elastic modulus from 0.34-1.37 GPa to 1.1-3.3 GPa, and an enhancement in Poisson’s ratio from 0.07-0.15 to 0.1-0.33. Therefore, lightweight calcium-aluminate cement formulations with PMHS treated FCS could preserve its mechanical performance after subjecting to thermal shock. We further incorporated the measured properties into a fully coupled thermoporoelastic model for wellbore integrity analysis. Results show that the novel PMHS treated FCS could resist large range of pressure and temperature perturbations during heat injection and production. Overall, this novel formulation could be a promising solution to the durability of the HT-RTES wells.

This paper presents a technological advancement in geothermal and energy storage technology with the development of a high-pressure Pelton turbine designed for deployment on the flowback cycle of well operations. Conventionally used at high-head hydroelectric sites, the Pelton turbine has been reimagined to harness high pressure held in deep wells, offering a new pumped storage approach.

The custom-designed Pelton turbine features a 3.2MW rating across a range of pressures from 3500-5000 psi, making it a unique but robust solution for extracting energy from high-pressure energy storage or geothermal reservoirs. With efficiency on par with pumped hydro storage facilities, this turbine introduces a scalable and cost-effective solution to geothermal energy extraction. This turbine technology will decrease the cost of energy storage or geothermal wells and power plants, making them a more likely solution for a source of baseload renewable energy.

The use of this technology in subsurface energy storage and generation industries marks a significant departure from traditional geothermal practices, as it now captures the abundant pressure available from pumping and flowing back water in wells, providing a simple yet highly efficient means of energy extraction. This has allowed recently tested energy storage concepts to be further developed, lowering the cost of geothermal applications, which harvest both pressure and heat, and become competitive with solar and wind.

The simplicity of the high-pressure Pelton turbine offers an affordable and scalable solution, paving the way for the widespread deployment of geothermal and energy storage wells. This paper discusses the design, performance expectations, and transformative potential of this technology, positioning it as a key player in the sustainable energy landscape.