KEM-39 Geomechanical and geochemical factors determining fault criticality during pressure (non) cycling of underground CO2, H2, N2 storage

The objective of the research question is to re-assess the causes of seismicity, specific risk factors including chemical processes in the reservoir, and safe operational bandwidths for reservoir storage conditions during pressure (non) cycling of underground storage of CO2, H2, and N2 in depleted gas fields.

To which extent does geochemical dissolution effects cause mechanical weakening of the reservoir or faults in the caprock? How is the formation pressure affected differently for the different types of storage fluid (fluid viscosity, density, compressibility)? This research question is a follow-up of the KEM-01 study, where storage of natural gas was studied, and it focuses on the specific issues related to the storage of other gases. Storage of CO2 ,H2, N2 in depleted gas fields may be a necessary measure in the energy transition. CO2 storage is currently being pursued offshore (Porthos) in the Netherlands. Research on hydrogen storage is currently focused on storage in salt caverns (UHS) but also storage in abandoned gas fields will be considered in the future. Nitrogen is currently being stored in a salt cavern near Heiligerlee. The nitrogen is being used to convert high-calorific gas to low-calorific gas to be used in the Dutch households for heating and cooking.

During the cyclic or more permanent storage of CO2, H2, and N2,seismicity could occur depending on the geological and operational parameters and chemical reactions in the reservoir. In this study, the factors controlling the reactivation of faults during storage of gasses is assessed for insights into the risks of energy storage. Buoyance effects or mixing effects with residual gases are not specifically taken into account for this study. This study will provide first insights in the difference between (cyclic) storage of other than natural gases on the probability of seismicity.

KEM RESEARCH QUESTION

The project results are six final reports, corresponding to the six work packages of the project. The final reports present a detailed investigation of the defined research questions based on literature review and numerical modelling. The numerical modelling is based on a one-way coupling, where the pore pressure is computed by the ECLIPSE software and then the pore pressure change is used as an external force in the geomechanical ATLAS software to estimate the point of activation with respect to temporal loading, maximum slip tendency, and maximum slip distance on the faults. These results were used in quantitative ranking of the analysed scenarios from the most to the least prone to induce fault activation.

KEM PROJECT REPORTS: WP1, WP2 + Annex, WP3, WP4, WP5, WP6

Based on simulation of a range of scenarios, the project concludes that the findings in KEM-01 for underground gas storage are also valid for storage of CO2, N2, and H2. A main risk factor is whether faults have slipped during the primary production of the reservoir. In this case, reservoir pressures during storage operations must be safely bounded. Based on the modelled scenarios, geochemical effects are negligible for CO2 storage. For N2 and H2 geochemical effects were not possible to quantify, due to lack of available data from laboratory experiments and case studies. 

The project was evaluated by the KEM scientidfic expert panel.

KEM PROJECT EVALUATION

Overall, the project has delivered very well. The literature review is sufficiently comprehensive, and the modelling is performed in a sound manner, with reasonable model assumptions and simplifications, given the scope of the project. Furthermore, limitations of the study and interpretation of results with respect to the available data are satisfactorily pointed out and discussed. With the deliverables provided, the KEM panel concludes that all research questions have been well addressed. A re-assessment of the project’s findings on geochemical effects causing mechanical weakening should be made at the point where more data from laboratory experiments and case stud ies becomes available. See also the Dutch project summary.