IEAGHG Faults and their Significance for Large-Scale CO₂ Storage Workshop 

Publication Overview

The success of CO? Capture and Storage (CCS) technology depends on the safe, secure and long-term storage of CO? at large-scale (mega tonnes per site). Upward migration and leakage of injected CO? along faults is a key risk. The aim of the workshop was to gain a greater understanding on how faults could influence long-term storage of CO?. The workshop built on oil and gas industry experiences, as well as the research community, to gain a clear perspective on fault properties that are important to CO? storage. The 1-day event provided an opportunity to review laboratory experiments, field studies, and modelling results, to gain insights on the importance of faults for CO? storage. Current practices to evaluate fault seal as well as critical technical gaps were discussed. The workshop gave an opportunity to review current research on CO? controlled release experiments and what could be learned from them, plus the contribution from simulations. The 1-day event documented critical issues for CO? storage related to faults, the experience of current experimental work, and identify remaining gaps in knowledge.

Publication Summary

• Faults are one of the pathways that CO₂ leakage could occur along (the seal being another).
• The risk imposed by faults is the key question.
• The petroleum industry has significant experience in how to assess and estimate the sealing capacity of fault systems, especially in the geological timescales. These same concepts could also be developed for a CO₂ injection timescale.
• Experience shows that cross-permeability is important, as is up-dip permeability. There is lots of experience and data on the lateral sealing of faults and the interaction of fault systems in 3D and fluid migration.
• Technology exists for deriving fault gouge permeability based on the stratigraphy and basin history, along with experimental data.
• The difference between CO₂ storage and the petroleum industry with regards to faults needs to be considered, as does CO₂ storage in areas where there is no oil and gas industry (and the implications of this on faults and potential leakage), noting that CO₂ injection operations are governed by location and engineering, whereas with hydrocarbon extraction there is no control over their location.
• Incorporating uncertainty is very important, as is modelling the uncertainty estimation.
• Current data is subject to bias towards fluids that are already trapped versus non-trapped and where to drill for success.
• There is an exposure bias in faults, for example they are easily identifiable in road cuttings and outcrops, meaning we don’t have great predictability, as yet, of fault architecture in the subsurface.
• We need to look for low-hanging fruit.
• There are lots of models but little experimental data for CO₂ migration through faults. However, there are many experiments regarding the release of CO₂ which are currently being planned or conducted and the Workshop attendees will look forward to the results. Current experimental programmes are focussing on faults at shallower depths, so the relevance to conditions at much deeper depths needs to also be considered.
• The comparison between experiments’ real benefits between different geologies, fault histories etc. is important and comparable measurement techniques are needed. These criteria need to be emphasised in the messaging of these results.
• There should be a focus on detection technologies.
• The incorporation of a more detailed geological context needs to be developed.
• There was a suggestion that because collaboration is so important, an organisation such as IEAGHG could work to help coordinate comparisons between future fault experiments.
• This workshop expressed the view that models may be predicting pressures that are higher than anticipated in reality.
• Work in the subject area has demonstrated the capabilities to model and couple multi-physics. Opportunities exist for taking these models to the next stage by incorporating complexity (the distribution of mechanical and hydraulic properties).
• It’s important to look into how much will stay in the formation or migrate (and stay) in the next formation.
• A key question to consider is the ranges of CO₂ and brine that could reach the surface, or other formations, under different storage conditions.