Microseismic monitoring plays a crucial role in ensuring the safety and integrity of large-scale CO2 storage projects. The recently concluded deliverable 1.2 from the ENSURE consortium, titled “Comparison of Different Sensor Technologies, Network Setups, and Noise Levels with the Aim of Quantifying the Acquisition Footprints at Different Sites,” presents a thorough exploration of sensor technology effectiveness.
In-Depth Sensor Technology Comparison
In WP 1 the ENSURE team has compared microseismic monitoring data obtained from diverse CCS sites. The work primarily focuses on data from the Quest CCS site in Alberta, Canada, and the Lacq site in Southern France, with additional data from the HNAR site in Norway.
The evaluation is centered around assessing the effectiveness and challenges in detecting and locating small-magnitude seismic events of various sensor technologies, including surface seismometer networks, distributed acoustic sensing (DAS) fibers, geophones, and accelerometers both in wells and on the surface.
The results reveal that a single string of downhole geophones has the highest signal-to-noise ratio (SNR) and is ideal for microseismic event detection. With advanced signal processing methods, we can significantly increase the ability to detect microseismic events recorded at surface geophones and using DAS. Especially array-processing techniques applied to dense surface station setups can help to further increase event detectability. In terms of constraining event locations, a single string of downhole geophones is suboptimal, primarily due to insufficient azimuthal coverage. Combining downhole geophones with surface nodes lead to much more stable event locations with significantly reduced location uncertainties. The single DAS string cannot be used for event location on its own since no directional information can be estimated. However, DAS can help to further constrain event locations in combination with the downhole and surface geophone data especially by revealing a more comprehensive picture of the entire seismic wavefield. Furthermore, co-located DAS and geophone string can also be beneficial for better understanding of DAS data.
DAS versus borehole geophones
The ENSURE consortium’s commitment to advancing sensor technologies not only fosters the safety and integrity of CO2 storage projects but also sets the stage for more effective and reliable microseismic monitoring. The detailed findings from this report serve as a valuable resource for optimizing sensor setups, thereby contributing to the evolution of future CCS technologies.
For more information, contact Steve Oates, WP1 lead (Shell).