The CarbonNet Project, jointly funded by the Federal and Victorian Governments, is investigating the potential for a commercial-scale carbon capture and storage (CCS) network.
Should the CarbonNet Project proceed, by 2030 the network will deliver carbon dioxide (CO2) captured from a range of industries based in Victoria’s Latrobe Valley, via an underground pipeline, to offshore storage sites in Bass Strait.
The first storage site is known as Pelican, which has at least 125 million tonnes capacity at P90 and at five million tonnes per year. Pelican will have three injection wells and one observation well.
Since 2010, the project team has completed extensive investigations which have been subject to independent review and certification, including detailed modelling of potential CO2 storage sites in Bass Strait.
The project’s well engineering study determined appropriate injection well designs for a (sub-) vertical well drilled from an offshore rig and a second option of high deviation angle (extended reach drilling) wells that could be drilled to the reservoir from onshore.
The conceptual well designs demonstrated technical feasibility for both injection operations. The study also considered the estimated injection zone injectivity and expected injection rates and wellhead delivery pressure with detailed vertical flow performance studies.
The cementing program for each string of casing was designed to bring cement back to surface. The study noted that Thermalock™ cement was recommended for each string and across the annulus.
At the relatively low pressure and temperature of the Latrobe Group, 13Cr grade pipe was recommended for the liner in the CarbonNet wells.
The study noted that spare or redundant wells also had to be considered in the event of an injection well failure, and for well downtime for periodic logging and integrity checks, to ensure that there would not be any upstream effect on facilities causing necessity for venting.
Furthermore, well design and site access had to be considered for ongoing monitoring of well integrity and potential well remediation to ensure injectivity.
Drilling commences
Following a series of studies, in December 2019, the Noble Tom Prosser drilling rig commenced drilling Victoria’s first-ever offshore appraisal well (OAW) for future carbon storage.
The drilling of the well would enable the collection of rock core samples from the proposed carbon storage reservoir. Core samples would provide further insights into the properties and formations of the rock layers below the seabed and confirm its suitability to store carbon dioxide.
The well was drilled conventionally using a 30 x 13 3/8 x 9 5/8 x 7 inch well design to a total depth of 1,500 metres beneath the seabed. Conventional cores were taken through the 8 1/2 inch hole section with wireline logs taken over both the 12 1/4 inch and 8 1/2 inch hole sections. The 7 inch liner was perforated to provide the conduit for injectivity testing before the well was abandoned to meet regulatory requirements.
More than 100 crew worked daily shifts for almost eight weeks to complete the well in January 2020. An extensive dataset was successfully recovered during the operation, including geological formation rock and fluid samples and high-quality wireline formation logs.
CO2 appraisal well results
The rock samples are currently being analysed in laboratories to confirm their detailed composition, physical properties including porosity, permeability and their strength and chemical resistance to CO2.
Along with the data acquired from the 2018 marine seismic survey, the well data will be used to model and assess the suitability of the site for long-term storage of CO2.
In August 2020, Earth Resources provided an update on analysis of the rock cores taken from the CarbonNet Gular-1 appraisal well.
Earth Resources detailed that over 250 plugs (samples) had been measured by that point and analysis was ongoing. The plugs were selected from along the whole length of the core, except for some sections which were preserved for future tests.
The porosity and the permeability were individually measured for each core plug. According to Earth Resources, the permeability of the reservoir rocks at Pelican is amongst the highest recorded in cores from the Gippsland Basin, with 70 per cent of the samples having a permeability greater than one darcy and 16 per cent greater than 10 darcies.
One darcy has been classified as an excellent reservoir, so CarbonNet has proven to have superb reservoir quality, based on both the offshore well drilling and a prior review of a database of 1,500 oil and gas wells in this basin.
According to Earth Resources, a final investment decision for the project is planned for 2024.