Geothermal Systems
Geothermal energy has been a proven renewable energy source in areas of the world where high temperature hydrothermal resources are close to the earth’s surface, and are an important resource for power and direct heating applications.
Conventional (Hydro-thermal) Geothermal Systems
A hydrothermal resource contains three key conditions:
- Heat – which increases with depth below ground
- A natural water source – to allow the heat to be brought to surface via the fluid
- Sufficient permeability – to allow the fluid to contact the heat in the ground
These conditions exist primarily at tectonic plate boundaries, where fissures in the rock allow very high temperature and high pressure fluid to be produced to surface. Depending on the temperature and pressure, the fluid may steam or very hot water at surface. There are currently hydrothermal power plants operating in over 30 countries, mainly along the “Pacific Ring of Fire”, such as the United States, New Zealand, and Indonesia.
Enhanced Geothermal Systems
However, hydrothermal resources do not occur in many locations that require base-load power or large amounts of hot water. While heat occurs at depth globally, in most locations there is no naturally occurring water source. Additionally, in sedimentary reservoirs there may be permeability. However hard rock is impermeable, and flow only exists in naturally or artificially created fractures.
If the wells are drilled into a reservoir that has natural permeability, such as a sedimentary basin, then natural hydraulic communication may exist between injection and production wells. This type of configuration is sometimes termed “sed heat.”
Geothermal resources that contain heat but do not contain a natural water source are generally termed Hot Dry Rock resources. In these cases, since there is no naturally occurring water, fluid is injected into the resource from surface through one or more injection wells. The water is then returned to surface through one or more production wells. These Enhanced Geothermal Systems (EGS) are typically drilled deep into solid, non-porous rock to access higher temperatures, and may be more than 5 km deep.
In these EGS configurations, water is injected into one well and flows through fractures in the hot rock to a second well. It is then produced to surface through the second well. On surface, the fluid or steam is used similarly to a hydrothermal application. It is either passed through turbines or Organic Rankine Cycle (ORC) to generate electricity, or used for direct heating needs, before the water is re-injected again.
With EGS, while fractures in the hot rock generally occur naturally, sufficient permeability between the two wells is usually created by stimulating or “hydro-shearing” the rock. This opens the naturally occurring fractures in the rock, or creates new ones.
There are also developments related to “closed-loop” EGS, sometimes referred to as Advanced Geothermal Systems (AGS). These systems either utilize existing wells, or use newly drilled wells, to create an in-well heat exchanger system. For these systems the fluid remains in the wells. For example, EAVOR Technologies has a system called the EAVORLOOPTM, where a number of wells and multi-laterals are drilled within the reservoir. Fluid then flows from surface through the injection well, through the network of multi-laterals, and to the production well. Heat is transferred from the reservoir via conduction from the rock to the fluid.
Geothermal Challenges
There are a number of technical challenges with both “conventional” (hydro-thermal) and EGS.
Challenges with Hydrothermal Operations
The severe environments of high temperature geothermal wells can pose a significant challenge in terms of well integrity, equipment performance, and reliability:
- Well barriers must be properly designed to prevent uncontrolled releases of reservoir fluids to surface. Ongoing monitoring of wellbore condition is important.
- Casing connection design is critical to ensure structural integrity and pressure containment of casing strings throughout the well life. Strain-based design is crucial since completions will typically experience plastic deformation.
- Flow assurance must be maintained through on-going fluid corrosion and scaling mitigation.
Challenges for EGS
Despite the promise of EGS to allow for geothermal anywhere, the challenges of efficiently recovering the available heat has limited the commercial success of EGS. While the above concerns exist for all geothermal applications, additional challenges are encountered with EGS:
- Sufficient reservoir volume and permeability must be created in the reservoir between the injection and production wells to avoid lack of fluid flow.
- Fluid Short-circuiting in major channels between the injection and production wells needs to be avoided to ensure sufficient heat transfer and avoid cooling of production fluid over time.
- Difficulty with drilling rate of penetration (ROP) may lead to very high initial costs, especially with non-vertical wells.
- Careful design and monitoring during drilling or stimulating activities needs to be done in active seismic areas to reduce induced seismicity concerns.
- Many EGS applications will require some type of pumping system, either to inject fluid, produce fluid, or both. Designing suitable artificial lift systems that are reliable and are capable of operating at high flow rates and high temperatures can be challenging.
Applying C-FER's Expertise
C-FER’s interest in geothermal developed for a few key reasons:
- It is a low-carbon renewable energy source that holds a lot of promise for base-load power and heating applications. Unlike intermittent energy sources, geothermal can provide “on-demand” energy regardless of season or atmospheric conditions.
- Our many years working with thermal energy operators in Alberta has equipped us to solve many challenges that are similar between the two industries.
We use a combination of numerical and testing capabilities that can be brought together to solve geothermal challenges.
Geothermal Project Examples:
C-FER has had the following involvement in geothermal projects:
- Developed a custom wellhead design for a geothermal operator (SE Asia)
- Completed a customized, ISO-based full-scale qualification test on premium well casing connections (SE Asia)
- Reviewed the fitness-for-service of severely damaged geothermal wellheads and wellbores (USA)
- Solved well servicing challenges by adapting technologies from Canadian thermal oil sands wells (USA)
- Completed a techno-economic assessment for the use of deep geothermal wells to provide hot water to oil sands extraction plants (Canada)
- Completed a techno-economic review of a novel geothermal production method (Canada)
- Taught the geothermal well design course in conjunction with the international Geothermal Rising conference (USA)
- Evaluated the feasibility of using titanium alloy for geothermal well casing with a focus on premium connection performance (SE Asia)
- Performed CRA casing analysis for geothermal operator (USA)
- Performed wellbore modelling and computation fluid dynamics (CFD) for a novel downhole geothermal technology (Canada)
Learn more about our areas of expertise
Oilfield Technologies and Methods
- Assess and implement oilfield technologies in geothermal wells
- Modify oilfield technologies for geothermal wells
Flow Assurance
- Assist operators with flow assurance issues through material testing, reliability analysis, accelerated aging testing, flow loop testing, chemical analysis, scale and corrosion management
- Demonstrate concepts/new technologies and their impact on EGS feasibility and economics
- Techno-economic feasibility analysis
- Sensitivity to depth, flow rate, completion, thermal gradient, fracture spacing
Full-scale Qualification Testing
- Premium and semi-premium casing connections
- Corrosion resistant alloy material evaluation
- Full-scale corrosive environment testing
- Packers and vacuum insulated tubing (VIT)
- Artificial lift systems
On-site Monitoring & Instrumentation
- Select the appropriate well equipment and operating procedures that balance reliability, performance and cost
Training Courses
- Thermal well design & integrity for geothermal wells
- Wellbore Thermal-hydraulics for thermal wells
- Qualification of tubular connections for geothermal wells
- Well deformation analysis using Well Xplore
Papers, Reports and Media Releases
World Geothermal Congress
- An Integrated Analytical Approach to Casing Connection Evaluation for Geothermal Applications
- Casing Connection Evaluation for High-temperature Geothermal Applications – A Case Study
- Evaluating Casing Deformations in Geothermal Wells Using Multi-Finger Caliper Data Analysis
Geothermal Research Council Annual Meeting
- An Introduction to Flow Control Devices and the Potential Benefits to Geothermal Applications
- High Temperature ESPs for Geothermal Production: The Ideal Pump
- Technical Considerations of Well Design and Equipment Selection for High Temperature Applications – A Canadian Perspective
Pathways Alliance
- Preliminary Assessment of Enhanced Geothermal Systems for Oil Sands Mining Operations
- Emerging Technologies: Advancing geothermal energy for mining
Geothermal Rising
GeothermalCanada.org
Contributors
Brian Wagg, MSc, PEng.
Director, Testing Services
With over 35 years with C-FER, Brian Wagg’s current focus is on applying C-FER’s analytical and full-scale testing capabilities to projects in clean energy including CCUS, hydrogen, geothermal and small modular nuclear reactors.
Kelly Piers, MSc, PEng.
Principal Engineer, Business Development & Strategic Initiatives
Kelly Piers is a Principal Engineer at C FER Technologies. In this position, Kelly works on strategic and business planning for C-FER and focuses on identifying, developing and implementing C-FER’s strategic diversification objectives, working with a number of industry associations in Alberta and across Canada.
Kirk Hamilton, BSc, PEng.
Director, Engineering Services & Sales
Kirk Hamilton works on strategic and business planning for C-FER and focuses on identifying, developing and implementing C-FER’s strategic diversification objectives. Kirk is a globally recognized expert in premium connection qualification execution and evaluation of methodology/techniques for high-pressure high-temperature, thermal, and unconventional applications.
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