KEM-24a Effect of reservoir pressure maintenance by fluid injection on seismic risks Groningen

Worldwide, the production of natural gas from subsurface porous reservoirs leads to surface subsidence and induced seismicity, caused by the compaction of the depleting reservoir. Fluid injection during or after production is a potential measure to control the reservoir pressure and, hence limit, reservoir compaction. This intervention may result in a lower risk of induced seismicity compared to scenarios without fluid injection.
The first objective is to investigate and identify what the best method is to model and quantify the effect of fluid injection on the expected seismicity risk profile. Two main factors will be considered: (1) using various injection fluids (N2, CO2 and water) or a mixture of natural gas and an injected fluid, and (2) different injection scheme options, including reusing existing production facilities. The second objective is to find a reliable method to assess possible additional seismic risks associated with fluid injection itself (as it might locally trigger seismicity) and to determine which factors, circumstances or injection configuration and volumes may increase the probability of seismicity and vice versa.
The overall objective is to assess whether the net effect of fluid injection on the seismic risk profile can be positive and to give recommendations to optimize the risk reduction at minimum injection costs.

FULL RESEARCH REQUEST

The objectives of this project were twofold: i) to investigate and identify the best method of modelling and quantifying the effect of fluid injection on the expected seismicity risk profile, ii) to find a reliable method to assess possible additional seismic risks associated with fluid injection itself (as it might locally trigger seismicity) and to determine which factors, circumstances or injection configuration and volumes may increase the probability of seismicity and vice versa. Injection fluids to be considered were N2, CO2 and water, or a mixture of natural gas and one of the injected fluids.

The deliverables are presented in three final reports: a report on literature review and input data compilation, a report on numerical modelling of pressure evolution during reservoir depletion and for various injection scenarios, and a report on the effect of fluid injection on seismic hazard. In addition, an umbrella report in two versions, Dutch and English, has been provided. This umbrella report provides a useful summary of the research objectives, methodologies, results, conclusions, and recommendations.

KEM PROJECT A SUMMARY (and in DUTCH)

KEM PROJECT REPORT B (WP0), REPORT C1 (WP1) and REPORT C2 (WP2)

The research team members of Fugro and Dynafrax were knowledgeable and skilled in their research areas and invested time and effort in all work packages. However, not all research questions and modelling tasks could be addressed. The research tools that were originally mentioned in the proposal (namely PFC3D and TOUGH3) for numerical modelling could not be used due to computational costs. As a result, some of the original research questions have been only partially answered or have remained unanswered.

Based on the results of this study, answers to the original research questions can be summarized as follows:

1.       Regarding the overall effect of fluid injection on seismicity no conclusive statement can be made. The fluid injection may be positive during significant production as average depletion and compaction can be stopped. Regarding possible injection scenarios after stopping production, it is concluded that seismic activities will decrease sharply after shut in anyway and injection will not lead to any significant reduction of seismicity.

2.       Regarding possible injection scenarios for pressure maintenance during production, it is not possible to give a definite answer. Injection should be avoided near Loppersum area because of the stress-criticality of Loppersum fault system and near production wells in order to avoid sharp pressure variations.

The KEM-24 has been evaluated by the KEN scientific expert panel.

KEM PROJECT EVALUATION

The main reason that conclusive answers to above questions could not be provided is that the main code used for numerical studies and its underlying assumptions proved not to be quite suitable for simulating Groningen field. The best option for numerical modelling would have been to couple TOUGH3 code with PFC3D, as was originally planned or an alternative code with similar capabilities or other suitable code. The question of how to adapt the Groningen seismic module for injection to account for pressure increase or decrease can therefore not be answered.

Additional research on this topic is recommended to better address the original research questions.

In November 2022, the Minister has sent a letter to Parliament on follow-up activities on this topic.