Produced Water Research Centre (PWRC)

Produced Water Research Centre (PWRC)

Simon George was a founding member of the Produced Water Research Centre (PWRC), set up in 2012 at Macquarie University.

https://www.mq.edu.au/research/research-centres-groups-and-facilities/secure-planet/centres/produced-water-research-centre-pwrc

Produced water is a term commonly used in the oil industry for water co-produced with oil and gas production. However it may be applied in a broader context to include water generated as a result of other industrial activities, including but limited to water generated from enhanced oil recovery, mining (water seeping from rock strata into open cut and underground mines), mineral processing, coal power generation, irrigation, food and fibre production and renewable energy generation. Produced water can be salty and/or contain other contaminants that may limit the options for its direct disposal or beneficial reuse, unless treated beforehand.

This is a new initiative and ideas are still developing. One possible project that could be developed is:

Geochemical, organic, and isotopic composition of coal seam gas and coal mining co-produced waters

A key aspect in the development and continuation of coal seam gas and coal mining projects is the need to gain a better understanding of the potential for connectivity between aquifer systems, including deep sandstones and the shallower sandstones that are typically used for anthropogenic activities such as agriculture, mining and human drinking water supplies. The Interim Independent Expert Scientific Committee on Coal Seam Gas and Coal Mining (Communiqué, Third Meeting – 26 March 2012, Canberra) state that an important strategic knowledge project to fill information gaps is the geochemical, organic, and isotopic composition of co-produced waters. These types of information will enable the fluid connectivity between successively deeper sandstone formations to be assessed, thereby enabling an understanding of whether re-injected co-produced water might leak into important water-supply aquifers.

This proposal suggests a comprehensive assessment of the geochemistry of the aqueous fluids in one or more coal seam gas plays. Indigenous fluids will be sampled from well sites, paying particular attention to obtaining fluids from several different sandstones zones in several different wells. In some cases, it will likely not be possible to separately sample different sandstones, due to co-mingling, and this will be noted during sampling. It is important that a survey such as this is done over a laterally extensive area, so that lateral persistence and connectivity of the sandstones can be assessed, and better data obtained on the likely lateral variability of aqueous fluids, as shown by their geochemistry. Controls on the geochemical signals may well be complex, reflecting the primary origin of the fluid, the water-rock interactions between the sandstone and the fluid (and thus the lithology of the unit will have a control on the fluid chemistry), as well as diagenetic reactions that will have occurred over the geological history of the sandstone.

The types of analyses likely to enable differentiation of fluids from different sandstones will include a range from some very basic geochemical parameters to some frontier and experimental geochemical and isotopic work. Salinity, pH and alkalinity will be measured on site, as soon as possible after sample production if possible, but are unlikely to be sufficiently discriminative. The carbon isotopic composition (δ13C) of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC), as well as the oxygen (δ18O) and hydrogen (δD) isotopes of the water will be measured, and may reveal information pertinent to the diagenetic history of the fluids. Organic compounds dissolved in the water will be measured, and may reveal interactions with organic-rich rocks such as coals, and also will enable assessment of any organic contaminants introduced through fracking or other drilling operations. Major elements will be important analytes, especially iron, and minor, trace and rare earth elements will also be measured. Fluid element chemistry is likely to correlate with lithology, and will be an important tracing technique. It is likely that some of the heavier elements will be more robust tracers than lighter elements, as the latter will be influenced more by alteration processes within the fluid. Key tracers for fingerprinting individual aquifers would include trace element patterns and ratios, such as the rare earth elements (REE), and potentially stable metal isotopes. The isotopic composition of elements such as lead, uranium, copper and iron will be investigated as stable isotopic fractionation of these isotopes will both be temperature (i.e. process) and source (i.e. lithology) dependent. Hence the potential exists to uniquely identify individual aquifers through an integrated geochemical toolkit.

Such geochemical data will then be interpreted in the context of establishing fluid history and the vertical and lateral connectivity of sandstones. There is rather limited literature in the use of this suite of techniques for understanding the connectivity of coal seam gas-related sandstones in Australia, and indeed in the World (e.g. Tweed et al. 2006, Vigier et al. 2005, Murphy et al. in prep). Accordingly, the first case studies that will be worked on will use and target a wide variety of analytes, and these will be refined in later case studies as knowledge about the best process and connectivity probes become apparent.

Thus the anticipated outcomes of such work will involve (a) characterisation of the primary aquifers (i.e. upflow), (b) comparison with downflow to monitor any changes in chemistry and (c) characterisation of fluids collected in situ within the production field. Interpretation of the data will then allow quantitative modelling regarding the degree of interaction between the sandstones.

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