Early Potential for Geological Storage Of CO2 in the Darling Basin of New South Wales (NSW), Australia

Abstract

The NSW CO₂ Storage Assessment Program and CO2CRC investigated the CO₂ geological storage potential of the Darling Basin NSW, Australia. Two exploration wells targeted Devonian sediments. Tiltagoonah-1 encountered silicified sediments that suggest poor CO₂ storage prospectivity for the Nelyambo Trough. Mena Murtee-1 (Pondie Range Trough) encountered several prospective reservoirs with low clay matrix, effective porosities of 5–12% and permeabilities of 10s – 100s mD. A new Pondie Range Trough static geological model adopted existing seismic horizon markers and a stratigraphic correlation between Mena Murtee-1 and Pondie Range-1. The prospective storage intervals are interpreted to be part of the Late Devonian Ravendale Interval of the Mulga Downs Group. A total pore volume storage capacity of 48 to 1730 Mt of CO₂ was established within the Pondie Range Trough (mean capacity of 650 Mt). Top and intraformational seal CO₂ column containment heights intersected at Mena Murtee-1 range from 26 m to 417 m. Analytical models and 2D radial numerical flow simulations predicted injectivity at Mena Murtee-1 and realisable storage capacity within the Pondie Range Trough. Results indicate single well CO₂ injectivity of up to 4 Mtpa within the depth range 1440–1640 m MD at Mena Murtee-1 without approaching fracture pressure. A realistic prediction of maximum injectivity across the trough is ~12 Mtpa utilising up to 10 injection wells, assuming lateral stratigraphic contiguity. Geomechanically modelled faults can support modelled increases in pore fluid pressure without reactivation. If present, low angle faults striking approximately N-S and high angle faults striking WNW and ENE would be the first faults to reactivate under excessive pore pressure change. CO₂ solubility under injection conditions was predicted to initially decrease pH from ~8.1 to 4.5. Over a modelled 10,000-year period, albite would dissolve, increasing pH to ~5.5; minor clays will almost completely dissolve while kaolinite, quartz and K-feldspar precipitate. Calcite dissolution and dolomite precipitation would together yield a net carbonate precipitation of ~5.5 moles from the equivalent of 1 kg of formation water. No significant storage risk was predicted to arise from CO₂ – water – rock interactions. Predictions arising from this study hold significant uncertainties but nevertheless, justify further appraisal of CO₂ storage potential in the Pondie Range Trough of the Darling Basin.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015