Rock physics & Interpretation

[RP-01] Using Surface Orbital Vibrators and DAS for Realizing Permanent Reservoir Monitoring – Lessons from the CO2CRC Otway Project

★ Invited

*Barry Freifeld¹, Roman Isaenkov^2,3, Konstantin Tertyshnikov^2,3, Sinem Yavuz^2,3, Pavel Shashkin^2,3, Alexey Yurikov^2,3, Evgenii Sidenko^2,3, Todd Wood⁴, Julia Correa⁴, Paul Barraclough³, Roman Pevzner^2,3 (1. Class VI Solutions, Inc. (United States of America), 2. Curtin University (Australia), 3. CO2CRC Ltd (Australia), 4. Lawrence Berkeley National Laboratory (United States of America))

Surface orbital vibrators (SOVs) combined with distributed acoustic sensing (DAS) presents a new approach to acquiring time-lapse seismic data. SOVs are AC induction motors mounted on fixed foundations, which spin eccentric weights, generating swept frequency P and S-waves (Freifeld et al., 2016). SOVs are built from off-the-shelf industrial components and unlike other rotary sources, there is no effort to provide phase-stability during rotation. A pilot geophone under the SOV allows for source-receiver deconvolution.

At the CO2CRC Otway Stage 3 Project, an SOV-DAS network was used to monitor the evolution of a 15 kT CO₂-rich fluid injection. Nine SOVs were operated as seismic sources and five wells are instrumented with DAS cables cemented behind casing. This installation was the first trial of dual-motor SOVs, which feature a smaller high-frequency vibrator collocated with a larger low-frequency vibrator, design to broaden the source spectral energy. Each SOV was operated for approximately two and a half hours every other day throughout a seven-month long baseline period, followed by an almost five-month injection period. Periodic 3D VSP surveys were conducted using conventional vibroseis to serve as a benchmark for comparison to the SOV-DAS data.

The SOV-DAS system proved highly reliable, operating with an uptime of ~95%. Challenges included difficulties in maintenance and operation associated with a complex system of hardware and software. Given the small changes associated with the thin gas plume, additional challenges concerned reducing noise and artifacts to maximize the time-lapse signature of the injected plume. This paper provides an overview of the SOV-DAS system and shares some of the lessons learned from one year of operation.