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Geologically Stored Carbon: Call for Public Consultation

Puro.earth is a carbon removal crediting platform. Through Puro Standard methodologies, we certify durable carbon removal and issue CO2 Removal Certificates, CORCs, per ton of CO2 removed and stored for at least 100 years. CORCs are issued and retired in the public Puro Registry, adding transparency to carbon markets.

In 2021, Puro.earth published version 1.0 of the Geologically Stored Carbon Methodology. This methodology has been extensively updated, and it sets the requirements for the eligibility and quantification of the net CO2 removal achieved over 1000+ years in suitable geological storage reservoirs.
The intention of this update is to evolve the methodology to correspond to the state-of-the-art knowledge on geologically stored carbon dioxide. The methodology covers the capture, transport, injection, and storage of the eligible CO2 streams, and provides improved requirements for the robust quantification of CORCs within suitable regulatory frameworks. The key updates in this methodology include the following aspects:

  • Eligible sources of CO2 – Carbon containing substances excluded
  • Eligible capture and storage processes – EOR excluded
  • Rules on baseline scenarios and determination of leakage enhanced
  • Quantification of CORCs detailed
  • Life cycle assessment detailed
  • Biomass sustainability criteria enhanced
  • Data collection and monitoring detailed
  • Risk assessment and management criteria enhanced

Period of Consultation

03 April – 24 April 2024


Puro.earth welcomes feedback from stakeholders and interested parties during this period, while the current update is being finalized. All feedback is valued as an integral part of our larger process of method development and review to ensure transparency and informed decision-making. 

Please download the Public Consultation documents and send your consultation feedback to contact@puro.earth using the downloadable form provided.


Consultation Documentation


For reference
Puro Geologically Stored Carbon Methodology 2021 v1.1 (current methodology)


Public Consultation Questions 
The following is a list of key questions that have been used to draft the updated version of the methodology. Please consider these questions whilst formulating your feedback and remember that you are welcome to provide your own feedback as well.


1. Is it necessary to set a purity percentage value for the eligible CO2 stream, e.g. 95%? Are the requirements for the composition of the CO2 sufficiently covered by the local legislation and regulations?


2. What evidence should be required to show that a depleted hydrocarbon reservoir is in fact depleted, and will not produce hydrocarbons anymore? Should a threshold value be set for any incidental oil/hydrocarbons recovered from the reservoir?


3. Are there other legal frameworks that can a priori be considered robust enough to provide an acceptable framework for safe geological storage than those mentioned in rule 3.2.11 b (i.e. US, UK, and EEA member states)?


4. Are the roles and responsibilities for carbon accounting and provision of evidence clear for the operators of the carbon capture, logistics and storage stages? If not, please specify what could be clarified.


5. Quantification of supply-chain emissions (via the LCA) are required to include upstream and downstream emissions. This implies that emission factors used in the calculation must not only cover direct emission (e.g. as in greenhouse gas inventory emission factors) but also upstream/downstream supply-chain emissions (e.g. as LCA emission factors provided in databases). Should the methodology allow for the use of emission factors that do not originate from LCA databases? If so, how should the missing upstream/downstream emissions be best included in the quantification? 


6. Quantifying and reporting supply-chain emissions (in the LCA) involves multiple parties (capture operator, logistic operators, storage operator). Each party has to quantify both its embodied emissions and operational emissions, and report those to the CO2 Removal Supplier (one of the parties) that synthesizes the information for the Puro Output Audits. Some of the LCA data will also be public in the Puro Registry.

a. All parties must comply with the accounting rules set out in the methodology. Is this feasible? Are there specific training needs of operators? Are there specific contractual arrangements needed between operators? 

b. In the case of shared infrastructure (e.g. a pipeline used by multiple CO2 Removal Suppliers), embodied and operational emissions from the shared infrastructure must be shared between the different CO2 Removal Suppliers (e.g. based on % share of CO2 transported for each supplier). At what frequency is it possible to report such % shares: annually (minimum required), quarterly basis, monthly basis, or higher frequency? 

c. Table 2 in section 5 of the methodology details how to structure the LCA calculations, but also details which emission contributions must be disclosed in the Puro Registry once CORCs are issued (marked with *). Is the level of detail suggested sufficiently transparent? Are there significant intellectual property concerns with respect to the level of detail suggested? Note that in any case, the full details of the calculations must be disclosed to the auditor for verification purposes.


7. Biomass Sourcing Criteria (section 3.7 in the methodology, and separate document): the Puro Biomass Sourcing Criteria define multiple options for evidencing the sustainability criteria (see details in the document), specific for each feedstock category. Should there be additional options for evidencing the criteria?


8. In Chapter 6, Determination of leakage, leakage sources for each removal pathway and baseline are identified, rules are defined to demonstrate mitigated leakage, and ultimately, non-mitigation leakage is quantified with specific rules. This approach is in line with the Puro General Rules 4.0. Are the mitigation rules defined in sub-section 6.2 relevant and feasible to demonstrate for each pathway, baseline, and leakage source? Should some be removed, modified, or new ones added? 


9. Are the requirements for the following topics feasible and adequate to ensure robust quantification of stored carbon?

a. Frequency of experimental measurements (mainly section 7 of the methodology)

b. Quantification uncertainty (section 4.8)

c. Reversal monitoring (section 7.6)

Please send your feedback using the downloadable excel form provided above and send the form to contact@puro.earth with the subject ‘Geologically Stored Carbon Feedback’.


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