Phase 3 of the Seismic Monitoring Network for the Horda Platform Region (H-Net) Project

Background and purpose of the project:

The industry partners of the Northern Lights full-scale CCS project (Equinor, Shell and Total) together with researchers at NORSAR and the University of Bergen are working on developing and demonstrating cost-effective monitoring of seismicity within the framework of the Norwegian storage regulations. HNET3 is the current project phase, leading up to planned start of injection in 2024 and building on earlier project phases called SNS-Net and HNET which were led by Equinor and NORSAR. These projects also build on many other CLIMIT projects aimed at maturing the technology for micro-seismic monitoring, including the DEMODAS “Distributed seismic monitoring” project led by CMR (now Norce), the “Induced-seismic geomechanics for controlled CO₂ storage in the North Sea” (IGCCS) led by NGI and the CO₂CAP/CO₂CAP2 projects led by NORSAR & SINTEF.

The overall goal has been to work out how CO₂ storage projects can effectively monitor seismicity on the offshore setting which is more challenging than for onshore projects. In the initial phase (SNS-NET) the project investigated solutions and options for seismic instrumentation onshore and offshore, and then in Phase 2 (H-Net) the project took the concepts further with the implementation of a new onshore array (HNAR) located on the Holsnøy island north of Bergen, while also demonstrating how offshore PRM nodes could be integrated with onshore detection arrays. In the current phase, the HNET3 project, the team will continue to use HNAR onshore monitoring array and also test out the use of new ocean-bottom seismometers.
This project is focused on the pre-operational CCS phase and aims to build a good understanding of natural seismicity. This background seismicity dataset will form the basis for assessing the nature of tectonic seismic activity before CO₂ is injected underground and will also allow the operator to more accurately assess possible induced seismicity during the injection period.

The overall goals of the project:

The Northern Lights project is the world’s first full-scale CCS project linking onshore industrial CO₂ emissions points to a dedicated offshore CO₂ storage facility (see https://ccsnorway.com/ for more information about the Longship project and Northern Lights). It is important for this CCS project and for future projects to demonstrate safe storage and to reduce uncertainties associated with long-term storage containment. While the integrated monitoring solution in the project is novel, it reuses existing technology and knowledge gained from offshore oil and gas operations and from onshore CO₂ storage monitoring projects globally. The technology is also used in global earthquake monitoring. Establishing the world’s first continuous microseismic monitoring array for an offshore CO₂ storage project will close a significant technology gap. A balance between cost and quality is also important to convince the world that large-scale CO₂ storage is feasible elsewhere as well.

Regulatory context:

In any CO₂ storage project, it is crucial to monitor where the CO₂ cloud is located during and after the project and to ensure site integrity. Real-time monitoring of seismicity is one of the key monitoring methods needed for confirming successful storage and ensuring long-term containment (i.e. avoiding the risk of leaks). The Northern Lights project is subject to “Regulations on the utilization of subsea reservoirs on the continental shelf for the storage of CO₂ and on the transport of CO₂ on the continental shelf” which require monitoring of stored CO₂.

Development of the technology in the project is important to meet the requirements of the following section of the regulations:
“The choice of monitoring techniques shall be based on best practices available at the time of design. The following alternatives shall be considered and used if possible: j) Technologies that can detect the presence, location and migration path of CO₂ in the subsoil and on the surface, k) Technologies that can provide information on the development of pressure and volume and area / vertical saturation of the CO₂ cloud (the plume) to improve numerical 3D simulations related to 3D geological models of the storage formation established in accordance with § 1-10 of this Regulation and Annex I, l) Technologies that can cover a wide area to retrieve information about previously undiscovered potential leakage paths over the area dimensions of the entire storage complex and above, in case of significant irregularities or migration of CO₂ out of the storage complex»
HNET3 project in brief:

Project runs from May 2021 to April 2024 with a budget of 10MNOK
Project goal: Efficient data collection, processing and interpretation in support of baseline seismicity assessment for CO₂ storage the Horda Platform region

Project participants: Equinor, Shell, TotalEnergies, Northern Lights JV, NORSAR, University of Bergen and Gassnova
Main activities in HNET Phase 3 Project:

A1: Routine operation of the HNAR seismic array (Holsnøy)
A2: Testing of offshore deployment of ocean bottom seismometers
A3: Advanced data analysis and interpretation research

– Automatic routines for joint processing of offshore nodes and onshore data.
– Improvement of the regional velocity model.
– Routine use of waveform correlation methods.

A4: Risk assessment and data integration.