Distributed seismic monitoring for geological carbon sequestration

DEMODAS seeks to develop DAS as a standalone technology or in combination with other technologies to serve as an Early Warning System for identifying risks during geological CO2 injection and storage. The project has developed an experimental prototype of a standalone DAS unit that has shown the capability of detecting hammer blows used to simulate micro seismic events. The results have been compared to geophone data, and indicate the potential for detection of risks during geological CO2 injection and storage. However, for external reasons, the system has so far not been verified for monitoring at actual geological CO2 injection and storage sites. Significant efforts have gone into the interrogator hardware design, and the design implemented in the last prototype has shown that NORCE?s phase sensitive DAS platform gives high fidelity responses to seismic disturbances. Data from the tests have been shared with the consortium members, and the unit will be an open access unit available for future research projects. Processing of DAS data requires conversion from optical to strain data. Substantial efforts were necessary to ensure stable results for the different approaches in hardware. This was achieved in close collaboration and exchange between the partners NORCE and NORSAR during the hardware development periods. Different field trials established test and verification data sets. Several controlled-source experiments using both horizontal and vertical fibre placements, we were able to establish the processing capabilities that can now be extended to microseismic processing on the full scale. A main focus has been on improving the signal to noise ratio, both through optimised hardware design and through data processing techniques. The results show that the signal quality has been significantly improved. Through testing at the laboratory in Trondheim, the project has verified that DAS technology can measure at locations 50 km away. Testing the last prototype developed in this project shows that also this technology has the potential to be used at such distances. Studies of faults and fractures increase the understanding of CO2 leakage in subsurface reservoirs. It shows how fracture and faults geometry control the upward flow of CO2, it is also another evidence that leakage are localized in areas of fault intersection. Therefore, in order to develop monitoring tools and to detect areas of CO2 leakage, relationship between active tectonism and spatial distribution of structural features are important knowledge

The three research partners (NORCE, NTNU and NORSAR) are continuing the research activities on DAS applied for CCS in new projects. The knowledge gained in DEMODAS is shared with the ECCSEL Svelvik CO2 Field Lab project team in the design phase of the Svelvik site. Though the Gundih field test, Indonesia was cancelled, Institute Technology of Bandung (ITB), Indonesia has been an active partner participating in three of the project workshops. ITB is involved in establish the first CCS site in Gundih, Indonesia, DAS is still a promising technology with huge potential, in particular as low-cost, permanent monitoring system. Key challenges remain, particular in data analysis before DAS will be routinely deployed in monitoring of CO2 storage sites. DEMODAS contributed in the understanding of the technology and the potential applications of DAS. The two industry partners will continue the DEMODAS activities by participation in an international project on applying DAS for CO2 storage

This collaborative project seeks to develop and demonstrate distributed acoustic sensing (DAS) technology applied to geological carbon sequestration. Field tests will be performed at NTNU's field lab in Trondheim and the CaMi Field Research Station (FRS), Canada. By combining DAS data acquired from buried fibre cables and borehole fibre cables during multi-source seismic excitation experiments, and passive long term monitoring of the injection process, DAS has the potential to reveal information that could be used for optimising the injection process and validating well and geological formation integrity. The combination of DAS data with complementary data from EM -wave, conventional seismic, and gravimetric methods may provide further enhanced capability. DAS is a low-cost technique that fits well into the portfolio of monitoring techniques needed to secure safe injection and containment of CO2. A cOTDR interrogation unit with software for controlling the unit and recording data will be designed and made. The unit will be verified by comparison tests with conventional geophone technology(WP1). WP2 will focus on the design of the microseismic and 3D VSP field experiments. The design work will take into account geological data and geophysical models. This ensures best experiment geometry at surface and depth for the buried fibre, as well as best configuration for the combination of acoustic source and the fibre cable. Full stack seismic data from base and monitor surveys will be analysed. Difference techniques will be used to identify anomalies. VSP data from DAS systems will be used to calibrate seismic data and rock physics models for supercritical CO2 will be used to model and help the interpretation. Further will time-lapse AVO methods be tested. Visualization techniques to enhanced seismic volumetric imaging will be provided and geo-modelling and flow simulations of the interpreted seismic data will be performed (WP3)