Smeaheia Natural Seismicity Network (SNS-Net): preparing for containment verification

Background and purpose of the project:
Since the start-up of storage in Sleipner in 1996, Statoil ASA has been a leader in carbon capture and storage technology (CCS: CO₂ Capture and Storage). Technology development within monitoring of the CO₂ storage projects at Sleipner and Snøhvit has been published in several scientific journals and utilization of knowledge and experience from these storage projects has been gained. There is also a desire to demonstrate cost-effective monitoring technologies within the framework of the Norwegian storage regulations.

NORSAR has a leading international position in the use and interpretation of micro-seismic information. NORSAR has also established a US-Norway collaborative project, CO₂CAP, with the Illinois State Geological Survey, Sintef Petroleum and UT Austin, Texas. CO₂CAP examines possibilities for improving the location of stored CO₂ by comparing information from active 4D seismic and VSP with micro-seismic in a common tomography. The technology around microseismic monitoring has matured in the last 5-10 years and the partnership is well positioned for further growth and development of the technology.

The project is divided into five phases, with decision gates between the phases. In phase 1 (this project), the solutions for seismic instrumentation will be investigated that are sufficient and cost-effective to establish the necessary background seismic level in the Smeaheia area. Here, both solutions on land and on the seabed will be investigated. For land-based monitoring, different array solutions must be evaluated in interaction with individual stations. The noise level on land will be evaluated and the geometry and distances between the stations will be optimized according to the noise and the target area. On the seabed, solutions for certain Ocean-Bottom seismometers, nodes and / or small layouts of seabed geophone cables will be evaluated. Power supply and data transmission are some of the challenges here.

Information from alternative subsea and onshore instrument layouts is the basis for calculations of how well the seismicity can be registered with different solutions. These are compared technically and financially to form a decision basis that deals with the professional value and quality of the proposed solutions as well as financial costs for the instruments, instrumentation and operation. A comprehensive cost / benefit analysis presents a recommendation for a monitoring design.

What was the goal of the project:
Smeaheia CO₂ storage project is the world’s first, dedicated large-scale offshore CO₂ storage project. It is important for future projects that the concept is documented safely; that there can be no uncertainty that CO₂ will remain in the subsoil. The monitoring solution will be new and unique, but the aim is to reuse as much as possible of the knowledge from offshore oil and gas, from onshore CO₂ storage monitoring as well as automatic collection and processing from nuclear test blast monitoring. The technology gap that is closing is to establish the world’s first continuous monitoring of an offshore CO₂ storage. A good balance between costs and quality becomes important so that we can show the world that this is feasible elsewhere as well.

In order to accelerate large-scale CO₂ storage in Norway and the rest of the world, it is crucial that the safety of the storage site and the control over where the CO₂ is located is sufficient at all times. Real-time monitoring of seismicity is one of the few monitoring methods that is suitable for continuously confirming how the voltage field in and around the storage site may change, and thus say something about the risk of leaks. Monitoring of background seismicity is a prerequisite for being able to see any changes in the voltage field caused by the injection, and to be able to distinguish these from natural, tectonic changes in the voltage field.