Temperature controls two separate outcomes here, and they move in opposite directions. Higher temperature speeds the oxidation of iron that frees hydrogen, so gas yield keeps rising with the thermometer [7]. Temperature also decides which minerals form, and the mineral assemblage is what determines whether dissolved CO2 ends up as a stable carbonate [8]. That is why the modelled storage optimum lands in a band of roughly 150 C to 200 C, only fifty degrees wide [9][19], while hydrogen keeps improving above it [10].
In the model, temperature, salinity and pH are three independent inputs [6]. A formation supplies them as one package, and the package is not adjustable. The fluid the model likes for hydrogen is low in salinity [11] and alkaline [12]. Whether any drillable interval of the Yilgarn Craton, one of Australia's oldest and best-preserved geological blocks [15], offers that alongside 150 C to 200 C is a question for a borehole rather than a solver.
The reported results are qualitative rather than quantitative: they show direction, not amount, for either product. The only quantities in the reported results are temperatures; salinity and pH arrive as directions, more or less, with no hydrogen yield per volume of rock, no injection rate and no cost [20]. CSIRO's Regina Sander, an experimental reservoir engineer and techno-economic modeller, calls the dual benefit a potential one, and says plainly that the conditions maximising hydrogen are not always the conditions maximising carbon storage [13][14].
The valuation argument survives that, in a weaker form. Large areas of the Australian continent contain the rock types these reactions need [17], and the Yilgarn's mafic-ultramafic units come out of the modelling with strong potential for orange hydrogen [18]. The reason to look at ancient basement at all shifts: iron-rich and magnesium-rich crust becomes a candidate reservoir rather than a foundation under the prospective stuff [16], though the arithmetic of a single well stays the same. A first project picks one temperature, and on this modelling the temperature that maximises hydrogen is not the one that maximises stored carbon [10][14], so one of the two products arrives as a by-product of the other.
