GRC Transactions, Vol. 45, 2021

Eavor-Lite Performance Update and Extrapolation toCommercial Projects
Matthew Toews, Michael Holmes
Eavor Technologies Inc.

Keywords
Geothermal, closed-loop, multilateral, load-following, Eavor-Loop, Eavor-Lite, Rock-Pipe,
district heating
ABSTRACT
Eavor-Lite™ is a full-scale demonstration project of a multilateral closed-loop geothermal system.
An update is presented based on ~16 months of operations and testing. The project is located near
Sylvan Lake, Alberta, Canada and 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 sealedwith a chemical completion technique, resulting in a large subsurface heat exchanger.
An update is provided on project construction, operations, and thermodynamic performance. A
transient thermodynamic model is used to history match the outlet temperature and demonstrate
the predictability of conduction-based systems. An analytical model is derived and closely tracks
the transient model and field data. This analytical model is then extended to case studies of a
district heating project and a high temperature electricity project, demonstrating that they can
produce predictable, low decline output over long timeframes. The high temperature case study
produces an average of 8 MWe over a 30-year operating period when controlled with a constantmass flow rate.
1. Introduction
Over the past decade wind and solar have been the renewable energy source of choice withincreased manufacturing economies of scale and improvements in technology contributing to a
precipitous decline in cost. Both wind and solar are variable power sources that produce
electricity when their fuel, wind or sun, is available. Advanced zero-emitting firm or flexible
technologies are needed for electricity grids to transition to a net-zero carbon future. Further, innorthern Europe and North America almost 50% of total residential and commercial energy
demand, and therefore carbon emissions, is for heating rather than electricity. These are two of
the fundamental problems facing the energy transition. The current market consensus on

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potential solutions to address these problems appears to be focused on Battery Energy Storageand Hydrogen. However, both technologies have technical risks, require significant capital until
they become viable, have many qualitative drawbacks, and are more expensive than geothermal
even at their 2050 projected costs on an aggregate grid level (Holmes et al., 2021).
Geothermal is a natural fit for these two unsolved issues but still only accounts for < 0.3% of theworld’s energy output. In addition, while conventional geothermal has had a flat or slightly
increasing cost per unit over the last decade, Wind, Solar, and Shale oil/gas wells have each showna tremendous cost decline driven by a repetitive, fast, manufacturing approach (Toews et al., 2020).
Geothermal has remained a niche solution partly due to its lack of scalability and speed.
Closed-loop systems can address these challenges and provide both heat and firm or loadfollowing electricity. These systems differ from conventional geothermal and Enhanced
Geothermal Systems (EGS) as they consist of a subsurface closed-loop heat exchanger, that relies
only on conductive heat transfer into a network of pipes, rather than reservoir or fracture fluid
flow. Several recent efforts describe the technical challenges and opportunities. The impact of welldiameter in a deep closed-loop system has been shown to be relatively small while the mostimportant design consideration is depth (Esmaeilpour et al., 2021). Thermal interference between
wellbores in a multilateral closed loop system has been investigated with a natural coupling
analytical method (Yuan et al., 2021). Specific capital cost of a multilateral closed-loop system
has been investigated along with various sensitivities, showing that drilling cost of cased lateral
sections is a challenge to achieving commercially viable economics (Malek et al., 2021). This
paper specifically addresses the progress made with multilateral closed-loop geothermal systems,
their technical and financial advantages (Table 1), and their commercial potential.

System design
Permeability
Parasitic power load
Induced Seismicity
Water treatment
Dispatchable

Hydrothermal or EGS

Multilateral Closed-Loop Systems

Open System: Brine produced from reservoir, fluid
exchange between system and geological formation
Hydrothermal requires a hot and permeable reservoir; EGS
creates a reservoir through fracking.

Closed System: Working fluid circulates in isolationfrom reservoir, no fluid exchange
No need for permeable reservoir or hydrothermal
source.

Requires an electric pump to circulate brine continuously

Driven by thermosiphon, no pumping required

Fracking or high injection pressures can lead to induced
seismicity. Seismicity has caused several failed EGS
projects in Europe, Asia.
Continuous water treatment issues that may include scale,erosion, corrosion, produced gases, NORMs
BaseloadIn projects with low enthalpy or high TDS brine, Opex canbe greater than Capex over life of project
Large initial output uncertainty prior to spending capex.
Even after operating for 5 years or longer, there remains
Thermal Output Uncertainty
substantial risk of precipitous drop in revenue due to cold
water breakthrough.

Operating Costs

Project Cycle Time

Typically 5-10 years or longer

No fracking, pressure-balanced, no induced
seismicity
Minimal water treatment, simply circulating abenign working fluid
Baseload and Dispatchable, able to time-shift
output while maintaining 100% capacity factor
Significantly lower due to inherent removal of key
Opex drivers
Thermal output predicted accurately prior tospending capital. No thermal output risk or
uncertainty.
~18 months, depending on regulatory regime

Table 1 - Comparison of Hydrothermal and EGS to multilateral closed-loop geothermal systems

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2. Eavor-Lite™ Project
To develop the base technologies required for a multilateral closed-loop system, the Eavor-Lite™
demonstration project was constructed in Alberta in 2019. The project is described in a previous
paper by the author and preliminary results were presented (Toews, Riddell, Vany, & Schwarz,2020). This paper provides an update to those results up to May 2021.
Eavor-Lite™ (Figure 1) is a full-scale prototype of the Eavor-Loop™ technology intended to derisk the key technical components. The project was partially financed through grants from several
Federal and Provincial agencies in Canada and Alberta: Sustainable Development Technology
Canada, Natural Resources Canada, Emissions Reductions Alberta, and Alberta Innovates. It
consists of a large U-tube shaped well with 2 multilateral legs at 2.4km depth, a test facility, and apipeline connecting the two sites at surface. It was constructed with two drilling rigs 2.5km apartthat drill and intersect these horizontal multilateral wells midway between the sites. The circulatingwater picks up heat in the subsurface loop, exits at surface, and the thermal energy is discharged
in an aerial cooler. The test facility is designed to allow the circulating water to be treated withadditives to enhance performance. The multilateral heat exchange section was sealed with RockPipe™ technology, a chemical sealing system that removes the need for steel casing. The wellcompletion design, multilateral junctions, multilateral wellbore intersections, and thermodynamic
performance is consistent with a commercial design.

Figure 1 - Eavor-Lite™ Schematic

The project was executed successfully, on-time and on-budget, demonstrating that an EavorLoop™ can be drilled, sealed, and operated purely driven by a thermosiphon effect withthermodynamic results in agreement with the predicted output from simulations. A summary of
the key technical objectives and outcomes is outlined in the Table 2.

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Technical Objective

STATUS

Summary of Results
LEG-2 was successfully intersected on September 1, 2019

1. Drill and intersect a multilateral EavorLoop with two laterals

LEG-1 was successfully intersected on September 11, 2019

Drilling program was completed and rigs were demobilized on September 14, 2019.

9 x formation integrity tests to 5 MPa performed throughout drilling and upon completion ofdrilling program with > 97.5% of pressure maintained.
2. Create a closed system by chemicallysealing the Eavor-Loop (Rock-Pipe™
completion)

Current operation leak off rate is < 0.5 m3/d.
Visual samples and filter differential pressure monitoring indicating negligible solids
production, facility has been running at ~95% uptime since Dec 4, 2019 start-up.
Thermosiphon has been fully operational, ongoing circulation without use of pump sinceDec 4, 2019 start-up.

3. Validate thermodynamic performanceand demonstrate thermosiphon

Thermodynamic model validation has been completed with measured performance within
2% of predicted.
Ongoing data collection and validation to prove out simulation capability over longer timeframe. Third party validation of results received from multiple organizations.

Table 2 - Summary of Eavor-Lite™ technical objectives and results

Construction of the pipeline and surface facilities was executed during October and November of
2019, and the entire facility was commissioned in December 2019. The facility has continued toperform without issue, operating consistently on thermosiphon mode (i.e. no pumping required)since December 4, 2019. Figure 2 illustrates some of the project components; there is also a virtual
tour of the facility and description of the process online at https://www.eavor.com/eavor-litevirtual-tour.

Figure 2 - Eavor-Lite™ Drilling Operations, initial Leg #1 intersection, and commissioning of the facility.

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2.1 Drilling and Intersection
Both Leg #1 and Leg #2 wellbore intersections were successfully achieved by PD Rig #241 on
Sept 1 and Sept 11, 2019, respectively. Wellbore ranging operations were executed flawlesslyon the LEG #1 segment – nearly a direct hit. After intersecting, we reamed into the target
wellbore 50+ meters taking measurements while drilling surveys throughout to further verify
mechanical intersection. See Figure 3 below where the target well (14-12) is shown in ‘green’
and the intersecting wellbore (06-01) is shown in ‘blue’. For Leg #2 a more typical intersection
was achieved, intersecting at a low convergence angle roughly 83m laterally back from the toe ofthe target well.

Figure 3 - Intersection diagrams, Leg #1 (L) and Leg #2 (R)

2.2 Rock-Pipe™ wellbore sealing
The vertical wells are cased with steel casing and cemented in place, following best practices
from the geothermal and oil and gas industries. However, the multilateral heat exchange section
is sealed with Rock-Pipe™, an Alkali-Silicate based sealant system. It is designed to:•••Permanently seal the near wellbore porosity / permeability while drilling the open holelaterals of an Eavor-Loop™
Maintain the seal during the operational life using working fluid additives and treatments
Maintain Wellbore Integrity throughout the operational life

Rock-Pipe™ has two primary components: the initial sealing phase function which is achieved
during the drilling phase, and the additives/ treatments deployed with the long-term circulating
fluid (“working fluid”) within the Eavor-Loop™. These additives maintain and improve theseal, by naturally leaking-off and plugging any remaining permeability. Further, the working

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fluid is designed to provide important well integrity functions such as chemical stability toshales/muds and maintain appropriate compressive strength to the formation.
In laboratory core flooding tests at in-situ pressure and temperature, the sealant penetrates
several centimeters into the core before setting into a solid. Results indicate the core does notcompletely plug off with the initial treatment, however >99.9% of permeability is lost.

Figure 4 – Rock-Pipe core, after sealing

The key performance indicator for success of the Rock-Pipe™ system is the operational subsurface leak-off rate. The measured daily leak off over time is shown in Figure 5. The steadystate leak off rate is only ~0.5 m3/d, despite the circulating fluid being over-pressured by ~2800
kPa relative to the in-situ pressure of the formation. The leak-off rate varies slightly withworking fluid chemistry yet remains below the 1 m3/d target for the project and continues totrend down over time. This rate of leak-off is immaterial to thermodynamic performance or
project economics.

Toews and Holmes

Figure 5 - Eavor-Lite™ Leak-off rate

2.3 Thermodynamic Performance
Thermodynamic performance of the Eavor-Lite™ project is measured and compared to thesimulated performance calculated using thermodynamic modelling software. Data has beencollected since start-up on December 3, 2019 which is then imported into Eavor’s transient 2D
thermodynamic model, described in (Toews et al., 2020) and (Holmes et al., 2021). The key
input parameters are inlet well pressure, temperature, flow rate, rock temperature and rockthermal conductivity. Using these parameters along with the wellbore geometry, the outlet
temperature and pressure of the system are calculated numerically by closing the energy, mass,and momentum equations for each discretized segment of the Eavor-Loop™ vertical and lateralwellbores. The prediction of the outlet temperature is directly tied to the amount of thermal orelectrical energy that the Eavor-Loop™ can produce.
Validating the model involves generating a history match of the empirical field results using themodel, then forecasting that model forward to predict future performance. A good history match
is obtained if the model accurately predicts measured values.
The transient 2D model was used to predict the measured performance data from Eavor-Lite™.
The model was history matched using 60 days of time series production data comprising outlet

Toews and Holmes
wellhead temperature, outlet wellhead pressure, and outlet well temperature at varying depth
measured by a 6-point thermocouple in the outlet well. Time series of measured circulation rate,
inlet wellhead temperature, and inlet wellhead pressure were provided as inputs. Properties of
the working fluid must also be accounted for as working fluid chemistry changes. History match
parameters were the rock thermal conductivities adjacent to the vertical and lateral wellbores.
The history match was performed using a genetic algorithm to minimize an objective function
specified as a weighted sum of squared error terms between the model’s prediction and themeasured data. Rock thermal conductivities, and accordingly thermal performance of the system,
were calculated to be within 5% of the values estimated prior to drilling the loop, highlighting
the predictability of closed-loop geothermal systems.
Figure 6 below shows the measured and predicted outlet temperature. The vertical solid blackline separates the data used for the history match (left) from the extrapolation and forecast(right). Circulation rate is shown for reference. Note that periods where there is no measured
wellhead temperature correspond to periods where the loop was shut down (circulation rate of 0)
for thermal recharge testing. To date, the model has been used to successfully predict over 16months of operating data with a mean absolute error of only 0.19°C (0.37%).

Figure 6 Comparison of Measured and Simulated outlet temperature results from Eavor-Lite™

A thermocouple string with 6 temperature measurement points was installed in the outlet well.
The model properly captures the potential energy and Joules-Thomson effects in the outlet well,matching all 6 thermocouple points closely.

Toews and Holmes

Figure 7 - Comparison of Measured and Simulated thermocouple data from Eavor-Lite™

2.4 Analytical method
A simple analytical equation can be derived to estimate the outlet temperature from a horizontal
lateral well. This equation is analogous with the approach developed by Ramey (Ramey, 1962)
for vertical wellbores under the key assumption that the heat transfer can be treated as quasisteady state radial heat conduction from the rock into the fluid flowing through the well bore.
The steady-state radial heat conduction equation is given by:𝑑𝑞𝑟 =2𝜋𝑘𝑟 𝑑𝐿(𝑇𝑟 − 𝑇𝑤 )𝑟𝑒𝑓𝑓𝑙𝑛 ( 𝑟 )𝑤(1)

Toews and Holmes
where 𝑑𝑞𝑟 is the incremental heat flow from the rock to the fluid in the lateral at a given axial
position
𝑘𝑟 is the thermal conductivity of the rock𝑑𝐿 is the incremental length in the axial direction
𝑟𝑒𝑓𝑓 is the effective thermal radius
𝑟𝑤 is the radius of the horizontal lateral wall
𝑇𝑟 is the temperature of the undisturbed surrounding rock
𝑇𝑤 is the temperature of the horizontal lateral wall
The steady-state heat conduction is based on an effective thermal radius for the rock beyond
which the temperature of the rock is unchanged. The effective radius varies with time and isgoverned by the non-dimensional Fourier number, Fo, for this transient radial conduction
problem:
𝛼𝑟 𝑡(2)Fo = 2𝑟𝑒𝑓𝑓
where 𝛼𝑟 is the thermal diffusivity of the rock; 𝛼𝑟 = 𝑘𝑟 /𝜌𝑟 𝐶𝑝𝑟
𝐶𝑝𝑟 is the specific heat capacity of the rock𝜌𝑟 is the density of the rock
The Fourier number is assumed to be a constant for this transient heat transfer problem with theprescribed geometry. Based on a linear, least-square regression against our numerical transientradial heat transfer model, Fo = 2.4675. Equation (2) can be re-arranged in terms of theeffective radius:𝜋(3)𝑟𝑒𝑓𝑓 = √𝐶𝑡 𝛼𝑟 𝑡 = √2.4675𝛼𝑟 𝑡~ √𝛼𝑟 𝑡2This equation (3) for the effective radius can be directly substituted into the “quasi” steady-stateheat conduction equation (1.1):𝑑𝑞𝑟 =2𝜋𝑘𝑟 𝑑𝐿(𝑇𝑟 − 𝑇𝑤 )𝜋 𝛼𝑟 𝑡)𝑙𝑛 ( √
2𝑟𝑤(4)

Here we assume that the thermal resistance due to convective heat transfer in wellbore is
negligible compared to the thermal resistance of the rock. Therefore, the temperature of thelateral wall, 𝑇𝑤 is essentially the same as the bulk fluid temperature, 𝑇𝑓 at a given axial location,i.e. 𝑇𝑤 ∼ 𝑇𝑓
The energy equation for the fluid flowing in a horizontal lateral be written as:
𝑑𝑞𝑟 = 𝑚̇𝐶𝑝𝑓 𝑑𝑇𝑓(5)

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Where 𝐶𝑝𝑓 is the specific heat capacity of the fluid flowing through the horizontal lateral and 𝑚̇is the mass flow rate.
Equating the incremental heat flow from the rock, equation (4) with the incremental heat flow
into the fluid flowing in the lateral, equation (5), yields:𝑚̇𝐶𝑝𝑓 𝑑𝑇𝑓 =2𝜋𝑘𝑟 𝑑𝐿(𝑇𝑟 − 𝑇𝑓 )𝜋 𝛼𝑟 𝑡)𝑙𝑛 ( √
2𝑟𝑤(6)

Re-arranging equation (6) and integrating it from the start to the end of the lateral:

∫

𝑇𝑓𝑜𝑢𝑡

𝑇𝑓𝑖𝑛

𝐿
𝑑𝑇𝑓
=∫
𝑇𝑟 − 𝑇𝑓0

2𝜋𝑘𝑟 𝑑𝐿𝜋√𝛼𝑟 𝑡)𝑚̇𝐶𝑝𝑓 𝑙𝑛 ( 2𝑟𝑤

(7)Assuming the fluid properties remain constant over the length of the horizontal lateral, equation
(8):

(8)

𝑘𝑟 is the thermal conductivity of the rock (W/m K)
𝐿 is the length of a single lateral in the axial direction (m)𝑚 is mass flow rate through a single lateral (kg/s)
𝑟𝑤 is the radius of the horizontal lateral wall (m)𝑇𝑟 is the temperature of the undisturbed surrounding rock (deg C)
𝑇𝑓𝑖𝑛 is the inlet fluid temperature (deg C)
𝑇𝑓𝑜𝑢𝑡 is the inlet fluid temperature (deg C)
𝐶𝑝𝑓 is the specific heat capacity of the fluid (J/kg K)
𝛼𝑟 is the thermal diffusivity of the rock; 𝛼𝑟 = 𝑘𝑟 /𝜌𝑟 𝐶𝑝𝑟
𝐶𝑝𝑟 is the specific heat capacity of the rock (J/kg K)
𝜌𝑟 is the density of the rock (kg/m3)
This analytical equation has several limitations. It assumed constant fluid properties and it is only
valid for horizontal wellbores. Despite these limitations it still provides a close match to the Eavor-

Toews and Holmes
Lite™ field data and the more complex numerical models. Figure 8 displays the measured datafrom the deepest thermocouple in the outlet well compared to the 2D transient model and theanalytical equation. Inputs into the analytical equation are in Table 3. Lateral length has beenadjusted slightly, from 1700m to 1900m, to account for the heat transfer that occurs within thevertical inlet well and build/turn section that is otherwise ignored in this analytical method.

Figure 8 - Analytical equation comparison

Average rock temperature
Inlet fluid temperature
Rock conductivity
Effective Lateral length
Mass flow
Wellbore radius
Fluid specific heat capacity
Thermal diffusivity

77.8
24
4.64
1,900
2.88
0.079
4.18
1.57E-06

°C
°C
W/m.K
m
kg/s/lateralmkJ/kg.K
m2/s

Table 3 - Analytical model inputs for Eavor-Lite™

Toews and Holmes
3. Commercial projects
Multilateral Closed-Loop systems can be applied to many market segments, such as
•
•
•
•
•

District heating or cooling in cities (i.e. as commonly found in Northern Europe)
Large scale (100’s of MW to GW capacity) baseload or flexible clean electricity
generation projects
Distributed electricity (i.e. behind-the-fence for data centers or industrial end-users)
Remote or Island Communities (currently generating energy with shipped or trucked
diesel)Resiliency markets (ex: Defense)

In each of these segments there are limited or no commercially available solutions to decarbonize
energy at a competitive price. The geometry and design of an optimum multilateral closed-loopsystem depends on the project specifics, the application, and the technological maturity of theunderlying components. Figure 9 shows the technical evolution of Eavor-Loop™, from theEavor-Lite™ project to the first projects being commercialized in Europe, and a deeper, hotter
version informally called “Eavor-Loop™ 2.0” which is currently under development.

Figure 9 – Eavor-Loop™ design evolution

Case studies are described below for a district heating project and a high temperature scalable
electricity project. The analytical method provides a simple, quick method with sufficientToews and Holmes
accuracy to evaluate commercial projects, and has been shown to closely match Eavor-Lite fielddata and more rigorous numerical models.

3.1 District Heating commercial project case study
District heating grids are common throughout Europe and in some locations in North America.
The required supply/return temperatures vary depending on the age of the network; forgeothermal in general it is more attractive to supply later generation networks with lower
temperatures. However, the biggest existing grids generally have high inlet temperatures. Table
4 shows parameters for a typical district heating system in Europe to replace coal-fired hot water.
Minimum network supply
temperature
Network return temperature# of laterals
Depth
Average rock temperature
Inlet fluid temperature
Rock conductivity
Effective lateral loop length
Mass flow
Wellbore radius
Fluid specific heat capacity
Thermal diffusivity

100

°C

55
12
4500
150
55
3.50
6,000
5.00
0.108
4.18
1.18E-06

°C
m
°C
°C
W/m.K
m
kg/s/lateralmkJ/kg.K
m2/s

Table 4 – District Heating case study inputs

Figure 10 shows the performance of this system, using the analytical model and a 2D transientmodel with a fixed flow rate of 60 kg/s (5 kg/s/per lateral). Since the analytical model ignores
heat transfer in the vertical wellbore segments, it is not expected to match exactly – however itstill shows a close approximation to the more rigorous numerical method.

Toews and Holmes

Figure 10 - District Heating case study output - constant flow rate

Figure 11 is the same well design, but rather than operating with a fixed flow rate, the flow rate
is varied automatically in the transient model to output the fixed temperature of 100 °C required
for the district heating system.

Figure 11 - District Heating case study output - constant outlet temperatureToews and Holmes
Another method of controlling the system is to operate with a fixed thermal output, as depicted
in Figure 12.

Figure 12 - District Heating case study output - constant thermal duty

3.2 High temperature electricity case study
Electricity generation is inherently more scalable than heating yet requires higher temperatures tobe cost competitive in the near term. Many areas of the western United States, Asia, Islands, andsome parts of Europe have regions with sufficiently high conductive gradients to reach an
average temperature in the multilateral section well over 200°C, particularly if the multilateral
section is not horizontal but extends deeper. This “Eavor-Loop™ 2.0” configuration is depicted
in Figure 9. Many Eavor-Loops™ can be directionally drilled from centralized surface pads toscale-up electricity generation to hundreds of MWs or potentially GWs. A generic example forsuch a project is described below in Table 5.
Net heat to power efficiency was calculated based on the outlet wellhead temperature, anassumed utilization efficiency of 50% relative to Carnot efficiency, and an assumed cold sinktemperature of 15°C.

Toews and Holmes# of laterals
Average rock temperature
Inlet fluid temperature
Rock conductivity
Effective lateral loop length
Mass flow
Wellbore radius
Fluid specific heat capacity
Thermal diffusivity

12
350
80
2.50
6,000
8.00
0.108
4.18
8.44E-07

°C
°C
W/m.K
m
kg/s/lateralmkJ/kg.K
m2/s

Table 5 – High temperature electricity case study inputs

As in the previous district heating example, the loop can be operated with a constant circulation
rate, constant thermal duty, constant outlet temperature, or with a variable flow rate designed toprovide shaped or flexible output (Reference sister paper). Figure 13 plots the thermal output
over time, if operated with a fixed circulation rate. The red line shows the peak output within thefirst several days, and the green line is the average output over 30 years. The peak output issomewhat irrelevant as this is constrained by surface facility design, but more importantly the
economics of a given project are dependent on the discounted average output, which isapproximated by the simple average shown in green.

Figure 13 - High temperature electricity case study output - constant flow rate

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4. Conclusion
The Eavor-Lite™ project has been successful in demonstrating the key technical components
required for a multilateral closed-loop geothermal system. A 2D transient model has been used
to history match the project using 60 days of data. After 490 days the model is matchingextremely closely, illustrating the predictable nature of closed-loop systems. An analyticalmodel has been derived that also closely matches performance.
Case studies have been presented for a district heating grid in Europe and a scalable hightemperature electricity project. Both the analytical and transient models confirm that asignificant thermal and electrical output can be produced, respectively. The high temperatureelectricity case study produces an average of 8 MWe over 30 years. Depending on operationaland economic considerations, the loop can be controlled with a fixed flow rate which results in aminimal decline over a 25-year operating life; or it can be controlled to have a constant outlet
temperature or constant thermal output.
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Vany, J., Hirschmiller, J., Toews, M., Subsurface Characterization Methods for Multilateral
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