Passive seismic imaging for CO2 geological storage in the Sudret area of Gotland, Sweden

Carbon capture and storage (CCS) is a strategy that can be employed to reducing human impact on climate change In the 21st century. Geological storage has been currently considered the most promising strategy. It is reported that there is a large theoretical capacity to store CO₂ in the Precambrian sedimentary succession of the Baltic Basin.

 

To aid in surveying and evaluating the potential storage reservoirs in the Baltic Sea, a seismic survey was performed over similar geology in the Sudret area of Gotland. Part of the survey consisted of 14-hours passive data, recorded along a 2.8 km profile with 10m receiver spacing and 1ms sample rate using 329 5Hz SmartSolo nodal units in the vicinity of two boreholes that had been drilled earlier.

 

We retrieved body wave and surface wave virtual shot gathers after applying signal separation and cross correlation calculations. For the body waves, conventional seismic data processing was conducted to obtain a stacked profile; for the surface waves, we could determine the dispersion curve in the frequency range 0.5 to 5.5 Hz and inverted these curves to obtain a velocity model from the ground surface down to c. 1500m depth.

 

Both the body waves and surface waves provide a high quality and high resolution image of the top of the Ordovician formation and have a good consistency with active seismic data in the same location. Moreover, they revealed some reliable deep geological information which active data cannot provide because of the limited source energy. Compared with active seismic exploration, passive seismic is friendly to the environment and cost effective. In some cases, it is an important complementary or alternative method to active seismic for CO2 storage and monitoring.