R. Pevzner, Curtin University
Stage 3 of the CO₂CRC Otway project has injected 15 kt supercritical CO₂-rich gas injection into saline aquifer at the Otway site, Victoria, Australia. For seismic monitoring using distributed acoustic sensing (DAS), five wells, four of which are deviated, were instrumented with highly sensitive fibre optic cables cemented behind the casing. Two different acquisition geometries were used, namely, offset VSP acquired continuously with a set of nine permanently deployed orbital vibrators (SOVs) acting as seismic sources and 4D VSP acquired with conventional vibroseis sources. 4D VSP survey comprises baseline and two monitor surveys, after injection of 4 and 12 kt of CO₂. The CO₂ injection commenced in December 2020 and ceased in April 2021, however the continuous monitoring using DAS/SOV combination is performed for a period exceeding 14 months, commencing in June 2020 and still ongoing as of August 2021. This provides both long baseline and post-injection monitoring data.
In this presentation we discuss the highlights of the seismic monitoring program and initial outcomes. A combination of the continuous monitoring and 4D VSP allows for an in-depth analysis of the time-lapse signal from the injection and different components of time-lapse noise, including the noise caused by surface condition variations, human activities, etc. Having the same plume imaged by data from several deviated wells gives estimates of uncertainties of seismic imaging.