GRC Transactions, Vol. 47, 2023

Eavor-Lite Update After Four Years Of Operation
Vlad Zatonski and Colin Brown
Eavor Technologies Inc.

Keywords
Geothermal, closed-loop, CLGS, multilateral, load-following, Eavor-Loop, Eavor-Lite, RockPipe
ABSTRACT
Eavor-Lite™ is a full-scale demonstration project of a multilateral closed-loop geothermal system
which has been in operation since 2019. The project is located near Sylvan Lake, Alberta, Canadaand consists of two 1.7 km long multilateral horizontal wellbores connecting two 2.4 km deep
vertical wellbores to create a U-tube shaped closed-loop geothermal system. The horizontal
wellbores are intersected using magnetic ranging technology, and sealed with a chemicalcompletion technique, resulting in a large subsurface heat exchanger. This paper includes updates
on:
••
•
•

Operation of the closed loop system
Predicted and actual thermodynamic performance.
Ongoing leak off monitoring and modelling.
A dispatchability trial and automated load following algorithm implemented in 2023.

A transient thermodynamic model is trained using early production history and forecast iscompared against actual performance demonstrating the predictability of conduction-based
geothermal systems.
Projects in various stages of development which were enabled by Eavor-Lite™ will be briefly
described along with some of the lessons learned during the operation of the pilot.
1. Introduction and Project Background
Eavor-LiteTM was constructed in Alberta, Canada in 2019. Eavor-LiteTM serves as ademonstration/pilot project to show various aspects of Eavor’s Closed Loop technology (EavorLoopTM) and serves as a platform for ongoing research and development.
Eavor-LiteTM is a full-scale prototype of the Eavor-LoopTM, consisting of large U-tube shaped wellwith 2 multilaterals. The laterals are approximately 1700m long and are placed in the Rock Creek
formation at depth of 2400m. See Figure 1.

Zatonski and Brown
Full extent of the project’s scope and goals is covered in great detail by Toews et al,. 2020 and2021.

Figure 1: Schematic of Eavor-LiteTM Pilot

2. Summary of prior publications
Eavor has presented at multiple conferences and published many papers demonstrating various
aspects of the Eavor-LiteTM Project.
Project scope, goals, timelines and execution are addressed in the Case Study of Multilateral
Closed-Loop Geothermal System paper by M. Toews, et al., 2020, while a paper by Jeanine Vany,
2020, goes to great depths to cover geological setting of the project, including thermal conductivity
modelling and geomechanics.
A one year update on the project, including thermodynamic modelling is described in the “EavorLite Performance Update and Extrapolation to Commercial Projects” by M. Toews, et al., 2021.
While the work by M. Holmes, presented in “Analysis: Multilateral Closed-Loop Geothermal
Systems as a Zero Emission Load-Following Resource” (2021) served as a basis for thedispatchability and load following algorithm which is covered in the later section.

Zatonski and Brown
3. Eavor-Lite operations
Since start-up, Eavor-LiteTM has produced close to 20 GWhth. The original temperature of theformation at TVD of 2400m was 78oC. After 4 years of operation, the outlet temperature is stableat ~ 50oC (at a production rate of 20m3/hr).
The project also serves as a testbed for Eavor’s Research and Development. Since the start ofoperations, many trials have been run at site to progress Eavor’s R&D and system understanding.
Most notable trials include:
••
•
•
•

Rock Pipe sealant augmentation – to show that Eavor’s chemical sealant (Rock Pipe),
which enables open hole completion of the multilateral section, can be reapplied after startup and develop procedure for seal reapplication.
Flow rate and operating pressure trials – test system behavior and predictability withmodels.
Shut-in trial – to illustrate system recharge and black start capability.
Fluid composition trials – test the effect of pH and viscosity on leak off.
Downhole camera inspection – inspecting wellbore condition, multilaterals andintersection point using a camera run on coil tubing.

3.1 Thermosiphon
One of the unique features of the Eavor-LoopTM is that the system can operate without a pump, up
to a certain flow rate – called the thermosiphon limit. Flow rates above thermosiphon limit require
the input of a pump.
At Eavor-LiteTM, the pump was only utilized for start-up and for various tests which require flowrate above thermosiphon limit. The total run time on the pump since start up is only 738 hours(compared to >30,000 hours of total system operation). For commercial projects, where trials andtests are limited, pumps will only be utilized for the initial start-up. Restarting Eavor-LoopsTM aftershut-ins do not require a pump, as the heel of the well (ex. Point C on the Figure 1.) has experienced
larger degree of thermal draw vs. the toe of the well (ex. Point D on the Figure 1.), making thesystem black start capable. (Even after prolonged shut down, due to the thermal drawdown, there
will be a temperature contrast between the inlet and outlet parts of the well).
3.2 Leak-offMultilaterals in the Eavor-LoopTM are uncased. The last stage of completions operations before
the wells are turned on is to apply the Rock-Pipe, which reduces the near wellbore permeability ofthe formation by several orders of magnitude.
Since Eavor-LoopsTM are operated above formation pressure, application of Rock-Pipe is anecessary step to reduce the leak off into the formation. The original in-situ permeability of theRock Creek formation, where Eavor-Lite’s laterals were placed, is estimated 0.5-50mD (500 –50,000 µD). Post Rock-Pipe application, the average permeability was reduced to 0.15-0.25µD, a
reduction of 3-5 orders of magnitude.
Current leak-off rate is ~0.4m3/d compared to a throughput of ~480 m3/d, indicating the system is
99.9% sealed. This leak-off rate is reducing slowly with time. Leak off can be predicted by a steadyZatonski and Brown
state – radial flow model, see Figure 2. (Note: the forecasted leak-off in Figure 2, uses constantoperating conditions - constant dP, and working fluid viscosity).

Figure 2: Historical leak-off vs. forecasted leak-off

3.3 History matching and production forecasting
The initial history match was trained on the first 60 days of data, optimizing for a series of variables
which had some uncertainty (ex. formation thermal conductivity). After the initial training, datafrom a hold-out set was used to ensure the match was accurate.
Following the initial training of the model, there were periods where the working fluid waschanged substantially (SG, viscosity, pH) for research purposes, which caused a minor discrepancy
either on the pressure or temperature matches. However, after the working fluid was stabilized (ex.
day 700), the match of forecasted data vs. actual showed very little error on both temperature andpressure plots (Figures 3 and 4).

Zatonski and Brown

Figure 3: Forecasted vs. actual Outlet Well Temperature (oC)

Figure 4: Forecasted vs. actual Outlet Well Pressure (MPa)Zatonski and Brown
The current error between the forecast and actual data is ~0.25oC and can be attributed to thechanges in working fluid properties due to the addition of corrosion inhibitor and biocides as wellas small fluid losses due to leak off.
3.4 Eavor-LiteTM Uptime
Since start-up the system has shown exceptional uptime of 96.2%, including any downtime
associated with system trials (such as dispatchability and thermal recovery trials, both of which
required a system shutdown). Outside of those trials, system reliability is 99.6% with the only
downtime attributed to a 3rd party power outage. As Eavor Lite does not produce any electricity(heat demonstration), power loss to site triggers a plant ESD for preservation purposes. Sincecommercial projects will produce electricity, PLC logic will be programed that in the event ofpower/grid loss, Eavor LoopTM flow rate will be reduced to match plant’s electrical load.

Figure 5: Eavor-LiteTM System Reliability

3.5 Load-following Algorithm
In a prior publication by Holmes (2021), the abilities of the Eavor-LoopTM technology as a zeroemission load-following resource (ZELFR) was explored. As a load-following resource, theEavor-Loop™ is capable of providing both baseload and dispatchable energy production to meetthe fluctuating demands of a population over a 24 hour period. Holmes and co-authors show thevalue that a ZELFR can bring as the globe trends towards net-zero electricity grids by providing
grid resilience and reducing overall system costs.

Zatonski and Brown
To take advantage of the Eavor-Loop’sTM ability to provide dispatchable energy, and meet a grid’s
energy requirements, the operator must be able to
1. Anticipate future energy demands from the grid,
2. Account for the physical heat transfer and energy storage mechanisms unique to the closedloop Eavor-LoopTM system, and3. Convert this information into actions to be enacted by the surface facility to achieve thefuture energy demand.
To perform these tasks manually would be onerous and difficult, especially as one’s interpretationof future energy demands changes with information that is constantly being updated.
To address these difficulties, Eavor has implemented a load-following algorithm at Eavor-LiteTM
to automate the three key steps outlined above to automatically produce a dispatchable energy
curve.
The algorithm is split into two separate models (orange nodes), and their functions are summarized
in the figure below:
Market & GridData

Measured operational outcomes used to actively re-tune the models

Weather Data

Energy Pricing
Data

Machine Learning
Model

Optimized energy
demand forecast

Physics-Based
Digital TwinModelInstructions forFacility

Optimized Energy
OutputContractualCommitments••
Other Data
Sources

Machine Learning model ingests
applicable data
Objective function set to optimize acertain operational outcome, e.g.
maximize revenue••

Digital Twin model converts theoptimized energy demand forecast into
actionable instructions for the facility
Digital Twin model continuously mirroring
live operations

Figure 6: Load-following algorithm high-level architecture.

The Eavor-LiteTM demonstration facility is not currently connected to the local power grid, and assuch the “Machine Learning” model has been replaced by a model that produces an energy
production curve to offset a typical electricity generation “duck curve” typical of grids with highamounts of wind and solar generation.
The figure below shows the thermal production from Eavor-LiteTM and the demand target set by
the algorithm over a 48-hour period.

Zatonski and Brown
Algorithm DemandEavor-Lite Production

Baseload Capacity

1Thermal Energy Production (MW)

0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0

Figure 7: Eavor-LiteTM load-following algorithm results over a 48-hour period.

To meet the input demand curve, Eavor-LiteTM reduces production and stores the energy in thesubsurface for production later in the day when it is needed.
The preliminary results show the algorithm does a satisfactory job of being able to convert anenergy demand curve into actionable instructions for the facility that ultimately yields a production
curve that closely matches the algorithm’s requested demand. Although the Eavor-LiteTM pilot of
the algorithm showcases a use-case in the presence of a wind/solar dominated grid, the algorithm
is highly customizable to different Eavor-LoopTM projects that may be operating in a variety ofenergy generation contexts.
4. Eavor’s Projects Following Eavor-LiteTM
To prove Eavor’s latest technologies such as Insulated Drill Pipe (IDP) and ability to drill in hot
dry rock (HDR), Eavor has recently completed a multi-lateral Eavor-DeepTM project in New
Mexico. Eavor-DeepTM reached depths of 18,130ft and drilled over 20,000ft of basement rock.
Rock Pipe, which has been developed at Eavor-LiteTM has also been used to seal Eavor Deep andreduce the leak off by a similar amount to Eavor-LiteTM.
The upcoming commercial Eavor-LoopTM project at Geretsried, which began drilling in July 2023
and was the recipient of a €91.6MM EU Innovation Fund grant, will consist of 4 Eavor-LoopsTM,
with 12 multilaterals each, and will draw on the experience and lessons learned of both EavorLiteTM and Eavor-DeepTM.

Zatonski and Brown
5. Conclusions
Eavor-LiteTM has been instrumental in showcasing and derisking closed loop geothermal
technology. The pilot project serves as a platform for development and validation of closed loop
thermodynamic models which accurately predict temperatures and pressures (<0.5% error intemperature prediction) after four years of operations and despite intermittent changes to theworking fluid for various trials. Monitoring of leak off helps provide better understanding of theleak off mechanism, while the R&D and trials executed at Eavor-LiteTM helped improve the RockPipe completions, leading to lower Eavor-LoopTM completions costs.
The transient thermodynamic model which was developed and validated was fundamental to thedevelopment and testing of load following algorithm which amplifies the value of Eavor-LoopTM
and allows the Loop to serve as zero emission load-following resource.
Lessons learned while operating the Eavor-LiteTM have been captured, documented and addressed
for future projects, which should result in lower operating costs (both fixed and variable).
6. References
Jeanine Vany, J. H. (2020). Subsurface Characterization Methods for Multilateral Closed LoopGeothermal Systems. Case Study of Field Scale Technology Demonstration Project in Alberta,Canada. World Geothermal Progress. Reykjavik.
Matthew Toews, D. R. (2020). Case Study of a Multilateral Closed-Loop Geothermal System.
World Geothermal Congress. Reykjavik.
Matthew Toews, M. H. (2021). Eavor-Lite Performance Update and Extrapolation to Commercial
Projects. GRC 2021.
Michael Holmes, M. T. (2021). Multilateral Closed-Loop Geothermal Systems as a Zero-Emission
Load-Following Resource. GRC 2021.