CCS Monitoring Using Time-Lapse Walkaway VSP in the West of China

The China’s first CCS demonstration project is a full process coal-based CO2 capture and multi-layer injection project. The CCS monitoring project in West China has deployed multiple phases of time-lapse zero offset VSP, offset Walkaround VSP, and 8 directional Walkaway VSP in Well Z-2 and using time-lapse VSP data processing and interpretation results to monitor the migration and spatial distribution of the CCS after the injection. This time-lapse VSP project adopts an integrated approach of theoretical study, survey design, data acquisition, processing and interpretation. Walkaway VSP data with good consistency with previous phases was acquired using a large downhole geophone array. Based on the 4th phase Walkaway VSP data, modeling test was conducted using the VSP survey geometry to verify the effectiveness of the time-lapse VSP monitoring method. Using the actual data, we studied the consistency processing workflow of time-lapse VSP data and VSP imaging technique and obtained high-resolution time-lapse VSP profiles. Through formation layer calibration and various attribute interpretations, the seismic response characteristics of VSP data before and after CO2 injection were analyzed, and the subsurface migration range of injected CO2 was predicted, achieving the expected monitoring objectives of CCS project.