A fractious debate

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Diagram extracted from submission opposing SAPEX's Arckaringa proposals by Dr Damien Bachmann.

ALTHOUGH THE SOUTH AUSTRALIAN STATE PARLIAMENT has passed a law which bans fracking in an area of the south-east of the state, the Department of Mines and Energy remains adamant that fracking, if conducted at depth and under stringent conditions, poses little or no risk.

It notes that up to the end of 2017 more than 900 wells in South Australia had been fracture stimulated (i.e. fracked) with zero negative impacts identified on water resources, soil, air quality, native vegetation and fauna, landscape and heritage, or the health and wellbeing of people or enterprise. 

Many of the fracked wells are in the Cooper Basin but typically these are around 3,500m down, about three times deeper than the proposed Arckaringa fracking.  The pressure of the fracking fluid required for in the Arckaringa, however, will be a lot lower.

SAPEX’s EIR notes; "Exploration in the Cooper Basin targeting unconventional reservoirs were large in volume and pressure (up to 14,000 psi). Injection pressure for a shale at 1,000m is expected to be between 3,500 – 4,000 psi."

The exact location of SAPEX wells has not yet been fixed, but the company says it intends to target the bottom of the Stuart Range Formation where it is up to some  250 metres thick.

Experience in the Cooper  suggessts that dependng on the pressure used, some of the induced factures could go above the top of the Stuart Range formation.  SAPEX says "In the unlikely event, a fracture propagated outside of the target Stuart Range Formation, the stress contrasts within the lower Mount Toondina Formation and the thickness of low permeability sediments will act as a barrier preventing any impact with the overlying GAB formations. “

This is disupted by geologist Dr Damien Bachmann, who argues that the type of silt in the lower Toondina means that the layers that SAPEX believes will provide an additional barrier to any leakage “are not necessarily continuous”.  

Dr Bachmann also notes that the federal government’s  2017  Bio-Regional Assessment of the Arckaringa says there is so much uncertainty about the composition of the Lower Toondina.Formation that “little can be implied  regarding the hydrogeological characteristics”.

In its assessment, the Department of Mines and Energy responded that SAPEX’s pumping pressure will be "such that the induced fracture network height is not expected to extend beyond 200m”.

It also noted that before any fracking takes place, SAPEX will have to seek Stage 3 approval, using detailed site-specific geomechanical data obtained from the initial drilling of the well.

Subject to Stage 3 assessment, the official watchdogs "deem there not to be any credible risk of fractures propagating into shallow aquifers and causing contamination or pressure depletion, in particular within the Great Artesian Basin".


 Indicative fracture stimulation depths,extraced from the SAPEX Environmental Impact Report.

SAPEX concedes: "There is evidence of connectivity via enhanced inter-aquifer leakage between the Great Artesian Basin and deeper target formations where the Stuart Range shale is thin or not present, (e.g. the Billa Kalina Sub-Basin). However, this occurs outside of the Boorthanna Trough and thus is not the target area for fracture stimulation."

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Indicative Stuart Range Formation Fracture Stimulation schematic showing stratigraphy, fracture extent and geological control provided by adjacent formations.   The Great Artesian Basin aquifers sit above the Mount Toondina formation                                     Source:  SAPEX Environmental Impact Report

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