Time-lapse VSP monitoring for CO2 injection: A case study in ordos, China

Carbon dioxide capture and storage (CCS) is considered one of the options for reducing atmospheric emissions of CO2 from human activities. Geological storage, as an important method to reduce CO2 emissions, may lead to a series of geomechanical problems due to the large amounts of gas injected. Starting in 2010, the Shenhua CCS demonstration project in the Ordos Basin, China, which is the first and the largest full-chain saline aquifer storage project in Asia, had injected a total of 0.3 million tons (Mt) of CO2 by 2015. The VSP method was used to monitor seismic properties. Baseline and repeat VSP surveys were conducted in May 2011 and August 2013, respectively. This paper focuses on the techniques of wave field separation and consistency processing. The upgoing P wave was used to image the time-lapse profiles by the VSP-CDP stack. Comparing the results, it was found that the time-lapse VSP method provides accurate and high-resolution images to monitor the CO2 diffusion range. The reliability of the method was then checked by the lithology of the target layer. With this current time-lapse VSP and geological analysis, the results showed that there is no obvious danger of gas leakage in the project, and that CO2 has been sealed in five predetermined reservoirs.