CO2 storage sites require ongoing monitoring and verification (M&V) to understand the behaviour of the CO2 plume stored underground.

Monitoring of CO2 stored in a deep saline formation (Stage 2C)

Seismic data can detect variations in the elastic properties of rocks, caused by changes in fluid saturations and pore pressure. Repetitive seismic (also known as time lapse seismic) is a powerful technology for to monitor such variations.

Variations in the elastic properties of rocks, caused by changes in fluid saturations and pore pressure, can alter the acoustic resonance of geological features and travel times of seismic waves. These can be detected using repeated seismic surveys.

The main objectives of the Otway Stage 2C project were to detect the injected Buttress gas (~79% CO2 and ~21% CH4) in the low-lying saline aquifer to ascertain minimum seismic detection limit, to observe the gas plume development using time-lapse seismic and to verify the plume stabilisation.

CO2CRC injected 15,000 tonnes of Butress-1 gas at a depth of 1,500m into the Paaratte Formation, a saline aquifer. The injection occurred between December 2015 and April 2016. The injection and evolution of the plume was monitored by a comprehensive time-lapse seismic program. It used a 1 km2 array of 908 geophones buried at 4m in lines spaced at 100m with 15m between each receiver and 40km of fibre optic cable deployed below-ground at 80cm, together with well-based Distributed Acoustic Sensing (DAS) fibre optics and 4D Vertical Seismic Profiling (VSP)to monitor the injected CO2. Mini vibroseis trucks were used as the source for each survey with approximately 3000 shot points in conjunction with two permanently deployed Surface Orbital Vibrators (SOV) for continuous monitoring. This entire activity went on without disrupting the peaceful life of the cattle farm at the ground level.

Seismic surveys were undertaken before injection in February 2015 (base line), then after 5,000, 10,000 and 15,000 tonnes. Two post injection surveys were also performed in 2017 and 2018. Seismic data analysis proved that a CO2 plume as small as 5,000 tonnes can be detected in saline formations. A joint analysis of the seismic images for original and monitoring surveys observes that the plume images from post-injection surveys are very similar. The plume signature is also clearly visible on the 4D VSP images and agrees with the results of the 3D surface seismic. An evidence-based conclusion therefore points to the stabilisation of the CO2 plume.

Other measurements acquired during Stage 2C have been in-zone and above-zone pressure monitoring during and post injection, interference well testing, Pulsed Neutron logging and downhole fluid sampling through U-tubes. The data acquired, including plume images from time lapse seismic, were used to update static models and history match the dynamic models of the Otway site. These models, were then used in combination with quantitative metrics to demonstrate the plume stabilisation over the long term.

Resulting Publications

Dance T, LaForce T, Glubokovskikh S, Ennis-King J, Pevzner R. 2019 Illuminating the geology: Post-injection reservoir characterisation of the  CO2CRC Otway site, International Journal of Greenhouse Gas Control, 86, 146-157.
link to publication reference

Pevzner R, Urosevic M, Popik D, Shulakova V, Caspari E Tertyshnicov K, Correa J, Kepic A, Dance T, Freifeld B. 2017, 4D surface seismic tracks small supercritical CO2 injection into the subsurface: CO2CRC Otway Project, International Journal of Greenhouse Gas Control. 63 p150 – 157.
link to publication reference

Pevzner R, Urosevic, M, Tertyshnikov K, Gurevich B, Shulakova V, Glubokovskikh S, Popik D, Correa J, 2017. Stage 2C of the CO2CRC Otway Project: Seismic Monitoring Operations and Preliminary Results. Energy Procedia. 114, 3997-4007.
link to publication reference

Globokovskish, S, Pevzner, R, Dance, T, Caspari, E, Gurevic, B, 2016, Seismic monitoring of CO2 geosequestration: CO2CRC Otway site case study using full 4D FDTD approach, International Journal of Greenhouse Gas Control, 49, 201-216.
link to publication reference

Christophersen A, Gerstenberger M, 2016 A Bayesian network and structured expert elicitation for   Otway Stage 2C: Detection of injected CO2 in a saline aquifer, International Journal of Greenhouse Gas Control, 51, 317-329.
link to publication reference

Caspari E, Pevzner, R, Gurevich B, Dance, T Ennis-King J and Dinar Y and Lebedev M. 2015. Feasibility of CO2 plume detection using 4D seismic CO2CRC Otway Project case study – Part 1: rock physics modelling Geophysics 80 (4) p 95 – 104.
link to publication reference

Pevzner R, Caspari E, Gurevich B, Dance T and Cinar Y. 2015. Feasibility of CO2 Plume Detection using 4D seismic: CO2CRC Otway Project case study – Part 2: detectability analysis, Geophysics vol 80(4) pp B195- B114.
link to publication reference

Michael K, Arnot M, Cook P, Ennis-King J, Funnell R, Kaldi J, Kirste D. & Paterson L. 2009. CO2 storage in saline aquifers I – Current state of scientific knowledge. Energy Procedia 1, 3197–3204.
link to publication reference

Tenthorey E, Dance T, Cinar Y, Ennis-King J, Strand J. 2014. Fault modelling and geomechanical integrity associated with the  CO2CRC Otway site 2C injection experiment, International Journal of Greenhouse Gas Control 1, 72-85.
link to publication reference

The Otway Stage 2C project delivered:

  • A broadly applicable procedure to predict, monitor and verify and assure CO2 migration and trapping in deep saline aquifers.
  • Demonstrated that as little as 5,000 tonnes of CO2 can be detected using seismic monitoring at over 1,500m below the surface.
  • An observation that 4D data quality, using a buried geophone array, is sufficient to observe time lapse evolution of the gas plume from as little as a 5,000 tonne injection with post stack repeatability of 10 – 20%.
  • Established a workflow to evaluate long-term plume stabilisation using seismic data, simulation models and a set of quantitative metrics.
  • An observation that with good levels of repeatability, offset VSP can be used to monitor the injection.
  • Findings that a Distributed Acoustic Sensing (DAS) array has potential for imaging the plume.
  • A finding that burying geophones and cables underground can reduce seismic acquisition time and decrease the footprint of a seismic survey. Higher data quality and 10% repeatable acquisition geometry also reduces the time for fast track processing.
  • A finding that data obtained using SOV single sweep data is of similar quality to that obtained by conventional vibroseis trucks, has higher repeatability and significantly lower costs, while minimising impact on landholders.
  • Detection of a 15,000 tonne plume of injected CO2 as it grew and stabilised deep in the subsurface using a range of seismic technologies.
One of the 906 geophones installed as part of the Otway National Research Facility’s Seismic Array
One of the 906 geophones installed as part of the Otway National Research Facility’s Seismic Array

Data obtained using SOV is of similar quality to that obtained by conventional vibroseis trucks, has higher repeatability and significantly lower costs, while minimising impact on landholders.

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