Standardized Resource Evaluation Methodology for Geothermal

Benjamin M. Hubbard, P.E.

Principal, Geothermal Advisory

What Is a “Standardized” Geothermal Resource Evaluation Methodology?

The viability of geothermal projects hinge on reliably characterizing the subsurface and translating it into bankable reserves and resources. Subsurface variability can produce wide ranges in volumetric estimates, well deliverability, decline rates, and ultimately in levelized cost of heat and/or power. A standardized, defensible resource and reserve evaluation methodology gives developers, investors, lenders, and regulators a common language. It defines classification boundaries, documents uncertainty consistently and transparently, and makes like‑for‑like comparisons across geographies and development concepts possible.

Consistency is fundamental to rapid industry growth. For developers, it shortens decision cycles and focuses capital on the best‑fit concepts. For lenders, it allows for clear comparison across technologies and geographies. For policymakers and utilities, it underpins how geothermal contributes firm, low‑carbon energy capacity. Above all, a consistent approach directly promotes financial interest, anchoring debt facilities and attracting equity investors. It also generates a third-party technical summary that can serve as project technical due diligence, accelerating investor interactions.

Why Do Geothermal Resource Evaluations Produce Different Results?

Geothermal assessments can diverge for reasons that seem small at the outset but compound throughout the analysis:

Data Heterogeneity in Geothermal Projects

Data heterogeneity: In addition to projects with missing or incomplete data sets, without a standard hierarchy of evidence, two teams may weight the same dataset differently, generating materially different conclusions.

Concept Drift Across Geothermal Development Concepts

Concept drift: Geothermal systems are often evaluated using analog tools, yet various development concepts differ in temperature regimes, flow assurance risks (e.g., scaling), well paths, stimulation/permits, and surface integration. Applying undifferentiated decline or capacity factors can skew economics.

Terminology Gaps in Resource Classification

Terminology gaps: Terms such as “resources”, “reserves” and “recoverable heat” are generally not interchangeable. Inconsistent terminology leads to confusion during fundraising efforts.

Risk Stacking in Geothermal Project Evaluation

Risk stacking: Exploration, drilling, stimulation, and surface-integration risks are sometimes blended into a single discount rate, masking where risk mitigation is needed. A standardized approach separates and quantifies these risks explicitly.

Documentation Gaps and Evaluation Transparency

Documentation gaps: Without a consistent audit trail—data lineage, model versions, sensitivity baselines—external parties cannot replicate results, and internal teams cannot efficiently learn from post‑drill variance.

A standardized methodology addresses each of these issues, providing clarity on what is known, how it is known, and identifying what is unknown.

What Are the Core Components of a Defensible Geothermal Resource Evaluation?

The following components are the backbone to developing a robust, repeatable technical and commercial evaluation that is transparent and auditable.

Technical foundation

Geological and Geophysical Model

Geological and geophysical model: Start with a clear conceptual model of the reservoir: heat source, permeability pathways (natural fractures vs. stimulated zones), caprock integrity, and fluid geochemistry. Each dataset must be ranked by resolution and uncertainty with a documented weighting scheme.

Heat-in-Place and Recoverability Assessment

Heat‑in‑place and recoverability: Calculate heat‑in‑place using consistent thermodynamic parameters and spatial discretion. Critically, recoverability factors should be differentiated by concept. The recoverability range should also be linked to analogs and to the project’s specific well architecture.

Well Deliverability and Decline Analysis

Well deliverability and decline: Adopt standardized decline archetypes per concept and document the physics behind any corrections for non‑Darcy flow, skin, scaling, and stimulation cleanup. Provide P10/P50/P90 deliverability curves with clear ties to data quality.

Surface Integration and Availability

Surface integration and availability: Translate subsurface thermal resources to net power (or process heat) with a transparent workflow: brine temperature and flow → binary/flash cycle efficiency → parasitic losses → seasonal ambient effects → net capacity factor. Availability assumptions should be evidence‑based.

Commercial and economic layer

Standardized Cost Libraries

Cost libraries: Use standardized cost libraries by region and concept: exploration (MT, seismic), drilling and completion (depth, bits, casing design, stimulation), surface facilities (turbomachinery, heat exchangers, cooling), and gathering/reinjection. Escalation indices and local content requirements should be explicit. Where vendor quotes are used, preserve them in the audit pack.

Revenue Architecture

Revenue architecture: Articulate the revenue stack: PPA tariffs, capacity payments, Renewable Energy Certificates, carbon credits, and heat offtake. For co‑produced and industrial heat projects, include process‑integration savings. Price scenarios must be clearly separated from technical contingencies to prevent double counting of risk.

Project Valuation and Discounted Cash Flow Analysis

Deploy DCF with scenario‑linked technical inputs (P10/P50/P90), to generate a probabilistic risk‑weighted valuation for exploration and development portfolios. Clearly separate systematic market risk (e.g., power price) from project‑specific technical risk.

Risk and uncertainty

Stage-Gate Risk Taxomony

Stage‑gate risk taxonomy: Define exploration, appraisal, and development stage gates with pass/fail criteria. At each gate assign a probability of success and define the cost and time at risk. Maintain a risk register aligned to technical due diligence items (e.g., scaling/chemistry treatment efficacy, long‑term thermal interference).

Sensitivity Discipline

Sensitivity discipline: Run standardized sensitivities: well productivity, thermal decline rate, capacity factor, capex overrun, drilling days, and tariff. Report elasticities in a format that ranks most impactful variables for driving value.

Geotechnical Audit Process

Geotechnical audit: Institute a geotechnical audit protocol—data provenance, model assumptions, calibration steps, and peer review. This creates consistency across internal teams and gives external stakeholders confidence that the evaluation can be replicated.

How Global Classification Frameworks Support Geothermal Resource Evaluation

While geothermal is distinct from hydrocarbons, the industry benefits from classification logic that separates geological certainty, project maturity, and socio‑economic viability:

UNFC Classification Framework

UNFC‑style axes group projects by: (E) socio‑economic viability, (F) feasibility/maturity, and (G) geological knowledge.

Applying PRMS Principles to Geothermal Projects

PRMS‑style thinking distinguishes resources from reserves by requiring not just recoverability in principle but also a defined development plan, demonstrated deliverability, and commercial context (offtake, permits, financing).

A standardized methodology should translate geothermal evaluations into these recognized frames without forcing a one‑to‑one copy of oil and gas definitions. The goal is clarity that protects capital and improves outcomes for stakeholders.

How Standardized Evaluations Improve Geothermal Project Finance

For lenders and investors, project viability hinges on three questions: Can the resource deliver? Can the project convert that resource to contracted revenue? Can the structure withstand downside? A standardized evaluation directly supports each.

Deliverability Assessment

Deliverability: A consistent workflow ties heat‑in‑place to recoverability and then to net capacity with traceable assumptions. Financiers can test downside by toggling documented P90 deliverability and decline.

Revenue Conversion

Revenue conversion: Standardized treatment of availability, parasitic losses, and seasonal ambient effects avoids optimistic bias in capacity factors. With a realistic net MWh availability, PPAs and capacity payments can be credibly benchmarked.

Project Resilience

Resilience: A uniform sensitivity package feeds directly into financing and structuring analyses. Structured properly, this enables tighter covenants and potentially lower financing costs.

Portfolio Risk Allocation

Portfolio effects: For funds and utilities, standardization allows portfolio‑level risk allocation. Exploration risk can be ring‑fenced; projects that clear appraisal gates can graduate into reserve‑class assets and different cost of capital. This improves capital efficiency and speed of deployment.

How Sproule ERCE applies a Standardized Geothermal Evaluation Methodology

Sproule ERCE brings a multidisciplinary team that marries geothermal geology and reservoir engineering with the commercial and regulatory fluency that investors, lenders and boards expect.

We integrate seismic, subsurface surveys, temperature gradient data, and geochemistry into calibrated reservoir models. Using concept‑specific recoverability factors, standardized sensitivities, and a geotechnical audit workflow, we produce evaluations that withstand investor and lender scrutiny. Our experience spans low‑, medium‑, and high‑enthalpy resources and compares conventional, binary, co‑produced, and EGS development pathways on a consistent basis.

Conclusion: Why Standardized Resource Evaluation Improves Geothermal Bankability

The geothermal industry is poised to scale significantly. But scaling requires clarity—on what is known, how it is known, and how uncertainties impact value. A standardized evaluation methodology strengthens lender confidence and lowers the cost of capital.

If you’re planning exploration, advancing appraisal, or preparing for a raise, Sproule ERCE can help you refine your methodology and produce an audit‑ready evaluation that stands up to technical due diligence.

Discover how this methodology delivers measurable, bankable outcomes in real‑world geothermal developments by exploring our Sproule ERCE Geothermal Case Studies.

🔗 https://sproule-erce.com/case-studies/?f_type=57