The Australian South West Hub Project: Developing Confidence in Migration Assisted Trapping in a Saline Aquifer – Understanding Uncertainty Boundaries Through Scenarios that Stress the Models

Abstract

Carbon Capture and Storage (CCS) is a critical technology to deliver step change de-carbonisation, or reduction of Carbon Dioxide (CO2), for industrial economies that are implementing climate change mitigation objectives. According to the European Commission Directive “Geological storage of CO2 in saline aquifers is considered a key option because of their widespread distribution and large theoretical storage capacity”. The South West Hub Project led by the Department of Mines, Industry Regulation and Safety (DMIRS) in Western Australia has been investigating and characterising the Lesueur sandstone as a potential target injection and storage formation since 2007. As expected with an unconfined saline aquifer, the project started with limited data, particularly when compared to sites based in oil and gas field areas. Working with research institutions and private sector expertise the project has judiciously acquired data on a stage gated decision basis. Starting with a 2D seismic over 110 line-km in 2011 and a deep well to 2,945 metres in 2012 the project was able to move through various modelling stages and uncertainty tables, before undertaking a complex 3D seismic over 115km2 in 2014 and then drilling three “shallow to intermediate depth wells” (1,350m, 1550m and 1,800m) in 2015 that gave good areal coverage, significant core and logging data on targeted critical sub-surface formations. As more information became available, so did the level of sophistication and granularity of the models: 2010: Generation 1 Models - >100 layers -10 million cells; 2013: Generation 2 Models –> 357 layers - 30 million cells; 2016: Generation 3 Models- >1,100 layers - 214 million cells. The SW Hub is unique insofar as it relies on proving primary containment through “Migration Assisted Trapping” (MAT - sometimes referred to as Migration Assisted Storage or MAS) in the Wonnerup Member of the Lesueur Formation, a 1,500metre thick relatively homogenous sandstone layer. Security of secondary containment is considered through the overlying paleosol packages in the Yalgorup Member, a 800M thick sequence of sand and paleosol deposits. Project activities are supported by R&D activities conducted under Australian National Low Emissions Coal Research and Development (ANLEC R&D). These projects are focused on reservoir characterization and either consider more fundamental physics based questions or delve significantly deeper into specific geology and geophysics domains using laboratory and modelling efforts. On occasion high resolution seismic, multi-offset VSP’s and other data has been acquired over targeted areas to illuminate certain parts of the reservoir. The research work is not the basis of project decision making but supportive to project efforts and complements private sector work through regular information exchange. Both the project activities and the research investigations target geological uncertainties and reduce risk for the project.