Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
ISO/TR 27915:2017 — Quantification and Verification of CO₂ in CCS Projects
Systematic framework for measuring, reporting, and verifying CO₂ captured, transported, and stored in carbon capture and storage systems
ISO/TR 27915: Quantification and Verification for CCS Projects
ISO/TR 27915:2017 establishes a systematic framework for the quantification and verification of CO₂ captured, transported, and geologically stored in CCS projects. Accurate quantification is essential for regulatory compliance, carbon credit trading, and public acceptance of CCS as a climate mitigation technology. The standard addresses the entire CCS chain — from capture at the emission source through transport to the injection site and long-term storage — providing methodologies for mass balance accounting and uncertainty estimation at each stage.
For CCS projects seeking to generate carbon credits under Article 6 of the Paris Agreement or compliance markets such as the EU ETS, quantification methodologies aligned with ISO/TR 27915 are becoming a de facto requirement for verification bodies.
The standard defines three quantification tiers, each with increasing accuracy and associated cost. Tier 1 uses default emission factors and simple mass balance approaches, suitable for screening-level estimates. Tier 2 incorporates site-specific measurement data and engineering calculations. Tier 3 employs continuous monitoring systems with rigorous uncertainty quantification, required for carbon credit generation and regulatory reporting in most jurisdictions. The choice of tier should balance the intended use of the data with the cost of monitoring infrastructure.
Measurement and Verification Methodologies
ISO/TR 27915 details specific measurement techniques applicable at each CCS chain stage. At the capture stage, CO₂ mass flow is determined using either direct measurement (flow meters combined with gas composition analysis) or indirect methods (carbon balance across the facility). The standard provides guidance on selecting appropriate flow meter technologies — orifice plates, ultrasonic, Coriolis, and thermal mass flow meters — each with distinct accuracy and reliability characteristics.
| CCS Chain Stage | Primary Quantification Method | Typical Uncertainty | Monitoring Frequency |
|---|---|---|---|
| Capture inlet | Carbon mass balance | ±5-15% | Daily / batch |
| Capture outlet (CO₂ stream) | Coriolis / ultrasonic flow + composition | ±1-3% | Continuous |
| Transport (pipeline) | Custody transfer metering | ±0.5-1.5% | Continuous |
| Injection wellhead | Coriolis flow meter + PT monitoring | ±0.5-2% | Continuous |
| Storage reservoir | Pressure / saturation monitoring | ±5-20% | Periodic / continuous |
| Monitoring wells | Geochemical sampling + pressure | ±10-30% | Quarterly / monthly |
The largest uncertainty in CCS quantification typically arises not from flow measurement but from the composition analysis of the CO₂ stream. Impurities such as N₂, O₂, Ar, H₂, and CH₄ affect both the measured flow rate (through density correction) and the actual CO₂ mass, contributing up to 5% additional uncertainty if not properly characterized.
Verification under ISO/TR 27915 follows a risk-based approach. The verifier assesses the quantification methodology, data quality management system, and uncertainty analysis. The standard introduces the concept of “materiality” for CCS — a quantitative threshold (typically ±5% of reported emissions reductions) below which discrepancies are considered immaterial. Verification statements include both the quantified amount and a confidence interval, enabling informed decision-making by regulators and carbon credit purchasers.
Engineering Design Insights for Monitoring Systems
From an engineering perspective, ISO/TR 27915 offers critical guidance on designing monitoring and verification systems that balance accuracy with cost. A key design insight is the importance of redundant measurements at critical mass balance nodes — particularly at the capture outlet and injection wellhead. Redundancy enables cross-validation and provides backup during instrument drift or failure, which is essential for maintaining data integrity over the 20-30 year operating life of a CCS project.
The standard also addresses the challenge of quantifying fugitive emissions — unintentional CO₂ releases from equipment leaks, venting, and mechanical losses. While fugitive emissions are typically small (0.1-2% of captured CO₂), they can significantly impact net storage effectiveness. ISO/TR 27915 recommends a combination of bottom-up (component-level leak detection) and top-down (facility-level mass balance) approaches for comprehensive fugitive emission accounting.
Large-scale CCS projects implementing the Tier 3 quantification approach recommended by ISO/TR 27915 have demonstrated measurement uncertainties below ±2% at the injection point, enabling reliable accounting of over 95% of injected CO₂ for regulatory and carbon market purposes.
Frequently Asked Questions
Q: How does ISO/TR 27915 relate to ISO 14064 and the GHG Protocol?
A: ISO/TR 27915 provides CCS-specific quantification guidance that complements the general GHG accounting frameworks of ISO 14064-2 (project-level) and the GHG Protocol. It fills gaps specific to CO₂ capture, transport, and geological storage that are not addressed in the general standards.
A: ISO/TR 27915 provides CCS-specific quantification guidance that complements the general GHG accounting frameworks of ISO 14064-2 (project-level) and the GHG Protocol. It fills gaps specific to CO₂ capture, transport, and geological storage that are not addressed in the general standards.
Q: What is the required accuracy for CO₂ quantification under this standard?
A: The standard does not mandate a single accuracy requirement. For Tier 1 (screening), ±15-30% may be acceptable. For Tier 3 (carbon credit quality), the standard recommends target uncertainty below ±3% at the injection point and ±5% overall chain uncertainty.
A: The standard does not mandate a single accuracy requirement. For Tier 1 (screening), ±15-30% may be acceptable. For Tier 3 (carbon credit quality), the standard recommends target uncertainty below ±3% at the injection point and ±5% overall chain uncertainty.
Q: How should stored CO₂ that remains in pore space be quantified?
A: The standard recommends using reservoir simulation models calibrated with pressure monitoring data and periodic seismic surveys to estimate the stored volume. The difference between injected and produced volumes, corrected for dissolution and residual trapping, provides the net stored amount.
A: The standard recommends using reservoir simulation models calibrated with pressure monitoring data and periodic seismic surveys to estimate the stored volume. The difference between injected and produced volumes, corrected for dissolution and residual trapping, provides the net stored amount.
Q: Are there specific requirements for third-party verification?
A: Yes. The standard recommends that verification be conducted by independent, accredited bodies with CCS domain expertise. The verification cycle should match the reporting period, typically annually, with more frequent audit for the initial years of injection.
A: Yes. The standard recommends that verification be conducted by independent, accredited bodies with CCS domain expertise. The verification cycle should match the reporting period, typically annually, with more frequent audit for the initial years of injection.
