Tracking a subsurface CO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si296.svg" display="inline" id="d1e313"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> plume with time-lapse pressure tomography in the Otway Stage 3 field project
Samuel J. Jackson, James Gunning, Jonathan Ennis‐King, Tess Dance, Roman Pevzner, Peter Dumesny, Paul Barraclough, Charles Jenkins
Abstract
We present results from a field trial of pressure tomography in the Otway Stage 3 project, Victoria, Australia. Pressure tomography involves the inversion of cross-well pressure test data to form a coarse-grained map of subsurface petrophysical properties, e.g. diffusivity-porosity-thickness. When performed in a time-lapse manner throughout CO2 injection, the gas saturation can also be tracked. Six wells, drilled at depth ≈1500 m in the Paaratte formation, are used to track the migration of 15 kt of injected CO2 with a series of cross-well pressure tests in three time-lapse surveys. We develop a Bayesian inversion scheme to infer the CO2 saturation in time, using two complimentary methods; a flow-agnostic adjoint method, and a topography driven gravity-current method. We present the methodology, post-processed data and maximum aposteriori probability (MAP) estimates of the plume migration, comparing to observations from seismic monitoring using time-lapse offset VSP and 4D-VSP. Results are consistent with seismic monitoring, with key features invertible from the time-lapse surveys: the centre of mass of the plume, the merging with an in-situ legacy gas plume, and the plume migration towards the monitoring array extremes. We demonstrate that pressure tomography is a viable, unobtrusive, long-term monitoring technique for carbon storage projects.