A combination of stratigraphic drilling and two dimensional (2D) seismic surveys are used in the NSW CO2 Storage Assessment Program to obtain information on the suitability of sedimentary units for CO2 sequestration.

Seismic surveys are used to evaluate the well locations and provide a seismo-stratigraphic correlation tool that can be linked to drilling information to produce a more robust geological model of the area.

Stage 1B

Stage 1B drilling activities were undertaken in early 2014 with the aim of investigating the CO2 storage potential and geothermal potential within the Nelyambo (Tiltagoonah-1 well) and Pondie Range (Mena Murtee-1 well) troughs in the northern half of the Darling Basin.

Rather than comprehensively characterising each formation, a data acquisition program was designed for Stage 1B with the aim of providing data that will eventually support a pre-competitive assessment of the potential of each targeted geological formation to safely and securely store CO2.

Darling Basin

Location of the Stage 1B wells, Darling Basin, central western NSW. The Group 8 Titles awarded to the NSW Department of Industry for the purposes of the Darling Basin Drilling Program are also shown (© NSW Dept. of Industry).

The substantial data and sample sets acquired from this exploration were sufficient to meet the needs of an initial geological interpretation of the near well lithology, which included the identification of reservoir/seal pairs as prospective intervals for CO2 geological storage.

Results

Results from Tiltagoonah-1 indicated that the sandstones intersected were heavily silicified and lacked porosity (i.e. tiny pore spaces within rocks required to hold/store injected CO2) and permeability (i.e. connection between the pore spaces to allow injected CO2 to flow from the injection point out into the storage reservoir), thereby rendering them unsuitable as a storage site for CO2.

In contrast, three sandstone units overlain by extensive claystone units were identified in Mena Murtee-1 as prospective storage reservoirs for CO2.

The existing offset well data along with seismic data and newly acquired data sets from Stage 1B exploration were used by collaborative researchers from the CO2CRC to undertake studies on the geological storage system characterisation, injection and plume migration modelling, geomechanical evaluation, and geochemical analysis and modelling. These studies provided positive indications for large scale storage of CO2 within the Darling Basin.

The prospective intervals encountered in Mena Murtee-1 were identified through low resolution injectivity and capacity modelling to have suitable porosity and permeability for CO2 storage. The computer modelling revealed that the porous sandstones may be capable of storing approximately 555 million tonnes of CO2. Thus, these sites could theoretically store the emissions captured from one large NSW coal-fired power station for around 40 to 50 years at an estimated low cost of between $21 and $23 per tonne.

A caveat is that this initial assessment of the Pondie Range Trough is based on limited exploration data, and hence holds a high degree of uncertainty. Additional exploration work is needed to confirm these initial results and also to identify other potentially suitable CO2 storage locations within the Darling Basin.

Stage 1B in the Darling Basin achieved its objective of investigating the CO2 storage potential and geothermal potential within the Nelyambo and Pondie Range troughs.

The discovery of prospective storage and seal units highlight the geosequestration potential of the Darling Basin and begin to confirm previous (limited data) Basin studies. An enhanced understanding of the geology of the basin has also been gained, and a large volume of subsurface data and drill core (114.39 m) were acquired. These have been made publicly available for continued assessment and study by government agencies, academia and industry. Concomitantly, key learnings were acquired that will assist in enhancing the outcomes of further exploration required to ascertain the storage potential of the Darling Basin.

For further information, the full CO2CRC Collaborative Research Report and the Final Report on Stage 1B – Darling Basin Drilling Program can be found on the DIGS (Digital Imaging of Geological Survey Reports) website.

Seeing is believing – Three-dimensional (3D) printed models of the porous sandstone

To assist in understanding the significance of the first discovery in NSW of a prospective CO2 storage reservoir in the Darling Basin, 3D printed models have been made of the porous sandstones extracted from the Pondie Range Trough (see image below). The printed models are enlarged replicates of a small plug (8 mm in diameter) of sandstone core from the Mena Murtee-1 well taken at a depth of 1,614 metres. They were produced from high resolution CT imaging of the plug.

On the left is the 3D model of the pore space (i.e. the voids between the rock grains) highlighting the actual connectivity between the rock pores that would facilitate the flow of fluids through the sandstone (NB. the connected rock pores are represented by the solid light-grey material that makes up the model). The model on the right shows the framework grains for the porous sandstone which is comprised primarily of quartz and several other minor mineral components.

Being able to visualise the pore space network highlights the attractive features of the prospective storage reservoir found in the Pondie Range Trough.

Stage 2

A second stage of exploration in the Darling Basin is currently being planned to verify and build upon the promising Stage 1B results.

Stage 2 concentrates on further investigating the Pondie Range Trough and neighbouring Poopelloe Lake Trough as a suitable storage site. Exploration is also focused in another promising sub-basin, the Yathong Trough, as an alternative storage option should further assessment of the Pondie Range Trough result in a downgrade in its prospectivity.

To achieve these objectives a comprehensive seismic survey and exploration drilling strategy is being planned. Coupled with comprehensive analysis, modelling and interpretation of the new data, the exploration program will allow a robust assessment of storage viability to be undertaken.

The Darling Basin in central-western NSW depicting the areas to be targeted in Stage 2 of the NSW CO2 Storage Assessment Program.

Planning of the Stage 2 Darling Basin exploration program has progressed in line with a developed work plan based on the:

  • consolidation and synthesis of existing data,
  • development of a peer-reviewed seismic acquisition program to fill existing data gaps, and
  • drilling of exploration holes located in key locations based on the outcomes of the new seismic acquisition.

A program of 2D seismic acquisition and processing has been planned as a precursor to the Stage 2 drilling. Planning for the Central Darling Seismic Survey is well advanced, with:

  • survey routes confirmed (including seven lines totalling approximately 186 km in length),
  • access agreements with relevant landowners secured,
  • local government approval to access public roads gained,
  • a procurement strategy with Geoscience Australia developed, and
  • planning approval processes near completion.

Landholder sentiment within the survey areas remains good with stakeholder engagement continuing between CINSW staff and landholders. Meetings have also been held with Central Darling Shire Council to inform and update them on the scope and progress of the seismic survey and further communication and engagement with local community members will occur via the Local Community Communication and Engagement for Darling Basin Drilling Program.

For further information
Coal Innovation NSW
Phone:
(02) 8229 2919
Rick.Fowler@planning.nsw.gov.au
ccs.info@planning.nsw.gov.au