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ISO 27916:2019 — CO2 Storage Using Enhanced Oil Recovery (CO2-EOR)
Quantification and documentation of CO2 stored in association with enhanced oil recovery operations
1. Overview of ISO 27916:2019
ISO 27916:2019 provides requirements for quantifying and documenting the amount of carbon dioxide (CO2) stored in association with enhanced oil recovery (CO2-EOR) operations. This standard, developed by ISO/TC 265, recognizes that CO2-EOR is primarily an oil recovery operation but that safe, long-term CO2 storage occurs as an inherent part of the process. The standard establishes methods for demonstrating safe containment of CO2 within the EOR complex and quantifying the associated storage.
CO2-EOR has been deployed internationally for decades. ISO 27916 provides the first internationally recognized standard for quantifying the CO2 storage that occurs as an intrinsic part of these operations, removing a key barrier to increased use of anthropogenic CO2 in EOR.
The standard applies to CO2 injected into oil and gas reservoirs for enhanced recovery where quantification of the CO2 that is safely stored long-term is sought. The standard is designed to work alongside other greenhouse gas quantification frameworks, including ISO 14064 series.
2. CO2-EOR Process and Storage Principles
2.1 Fundamentals of CO2-EOR
In CO2-EOR operations, CO2 is injected into oil reservoirs at pressures where it typically mixes with the oil, reducing oil viscosity and enabling it to flow more freely to production wells. The process is typically designed as a closed-loop system where some of the injected CO2 is co-produced with oil, separated in above-ground recycling facilities, and reinjected. This cyclic process results in a portion of the injected CO2 becoming permanently trapped in the reservoir through various mechanisms including miscible trapping, residual trapping, and dissolution in remaining oil and formation water.
| Trapping Mechanism | Description | Time Scale |
|---|---|---|
| Miscible/Structural trapping | CO2 trapped as a supercritical phase below caprock | Immediate to decades |
| Residual gas trapping | CO2 immobilized as disconnected droplets in pore spaces | Years to decades |
| Dissolution trapping | CO2 dissolved in formation brine or remaining oil | Decades to centuries |
| Mineral trapping | CO2 converted to solid carbonate minerals | Centuries to millennia |
2.2 Standard Boundary and Applicability
The standard defines the EOR complex as the three-dimensional geological volume encompassing the project reservoir, surrounding and underlying formations, and the sealing system. The standard boundary includes all injection and production wells within the EOR complex, surface facilities for CO2 handling and recycling, and associated measurement equipment. CO2-EOR projects using either miscible or immiscible displacement are covered, and the standard applies to both onshore and offshore operations.
ISO 27916 does not address site selection, characterization, or permitting for CO2-EOR projects, as these are covered by existing oil and gas regulations. The standard focuses specifically on demonstrating containment and quantifying storage.
3. Containment Assurance and Monitoring
3.1 Containment Assurance Requirements
The standard requires a comprehensive containment assurance program throughout the project lifecycle. This begins with geological characterization of the EOR complex to assess its ability to contain CO2, including evaluation of caprock integrity, fault sealing, and wellbore integrity of all wells within the complex. During operations, containment assurance is demonstrated through pressure management, monitoring of injection and production parameters, and verification that operations remain within the designed operating envelope.
3.2 Monitoring Program
A risk-based monitoring program must be implemented to detect potential leakage pathways and verify containment. Monitoring methods may include pressure monitoring, tracer surveys, seismic surveys, wellhead monitoring, and groundwater monitoring where applicable. The standard requires that monitoring methods be selected based on site-specific risk assessment, and that monitoring results be regularly reviewed to confirm that containment is being maintained.
The monitoring program for CO2-EOR benefits from the extensive operational data already collected during oil production operations. Pressure data, production rates, and injection profiles provide valuable information for containment verification.
4. Quantification Methodology
4.1 Quantification Principles
The quantification of CO2 stored in association with CO2-EOR follows a mass balance approach. The quantity stored (m_stored) is calculated as the total CO2 injected (m_input) minus CO2 losses (m_loss), which include operational losses, entrained CO2 in produced oil and gas, CO2 transferred off-site, and any leakage from the EOR complex. The standard provides detailed formulas and calculation procedures, with example calculations in Annex B.
| Quantification Parameter | Description | Measurement Method |
|---|---|---|
| m_input | Total CO2 injected into the EOR complex | Flow metering at injection wells |
| m_loss_operations | Operational losses (venting, flaring) | Direct measurement or engineering estimates |
| m_loss_entrained | CO2 in produced hydrocarbon products | Sampling and analysis |
| m_loss_leakage | CO2 leakage from the EOR complex | Monitoring and verification |
4.2 Allocation of Anthropogenic CO2
When only a portion of the injected CO2 is from anthropogenic sources (captured from industrial processes), the standard provides an allocation ratio methodology to determine the anthropogenic share of the stored CO2. This is particularly important for regulatory reporting and carbon credit calculations. The standard also includes provisions for avoiding double-counting when CO2 is transferred between different projects or accounting frameworks.
5. Project Termination and Post-Termination
When oil recovery operations cease, the standard requires a termination plan that addresses the long-term fate of the stored CO2. Periodic assurance of containment must continue until the operator can demonstrate that the CO2 is permanently trapped and no longer poses a leakage risk. The standard emphasizes that CO2-EOR project termination does not necessarily mean the end of containment assurance obligations — long-term stewardship may be required.
Unlike dedicated geological storage (ISO 27914), CO2-EOR projects are primarily oil recovery operations. When EOR operations cease, the operator must ensure that the CO2 storage aspects are properly closed out, including well abandonment and long-term monitoring commitments.
6. Engineering Insights for CO2-EOR Storage
Key engineering considerations from ISO 27916:2019 include:
- Quantification accuracy depends critically on measurement quality at injection and production points. The standard requires meters with appropriate accuracy class and regular calibration.
- De minimis losses (below a defined threshold) may be excluded from quantification, but the threshold must be justified and documented.
- Historical EOR projects can apply the standard retrospectively if adequate data exists, providing an opportunity to quantify storage from decades of existing operations.
- The standard recognizes that CO2-EOR storage quantification results can be combined with capture and transport quantifications for a full CCS chain accounting.
ISO 27916:2019 closes a critical gap in CCS standardization by providing a robust framework for quantifying CO2 storage in EOR operations — a proven technology with decades of operational experience.
7. Frequently Asked Questions
Q: Is CO2 stored during EOR considered permanent?
A: Yes, when properly conducted, CO2-EOR results in long-term storage through multiple trapping mechanisms. The standard requires demonstration of safe, long-term containment.
A: Yes, when properly conducted, CO2-EOR results in long-term storage through multiple trapping mechanisms. The standard requires demonstration of safe, long-term containment.
Q: Can ISO 27916 be used for carbon credit verification?
A: Yes, the quantification results can be used as input for greenhouse gas reporting programs, carbon credit schemes, and other regulatory frameworks.
A: Yes, the quantification results can be used as input for greenhouse gas reporting programs, carbon credit schemes, and other regulatory frameworks.
Q: Does the standard require 100% measurement of all CO2 flows?
A: Not necessarily. The standard allows for engineering estimates of de minimis losses and provides missing data procedures. However, all significant CO2 flows must be measured or accurately estimated.
A: Not necessarily. The standard allows for engineering estimates of de minimis losses and provides missing data procedures. However, all significant CO2 flows must be measured or accurately estimated.
Q: How does ISO 27916 handle CO2 that is produced and reinjected?
A> The standard uses a mass balance approach that accounts for the closed-loop nature of CO2-EOR. The net storage is calculated considering the full injection-production-reinjection cycle.
A> The standard uses a mass balance approach that accounts for the closed-loop nature of CO2-EOR. The net storage is calculated considering the full injection-production-reinjection cycle.
