Some Current Challenges in Production Geochemistry

Abstract

Power production from geothermal energy could be considered a mature technology. However, some comparatively recent advances have presented new challenges in production geochemistry.

The first is the use of pH modification to handle geothermal brines that are grossly oversaturated with silica. Although pH modification has been used previously with Salton Sea brines, it has only recently become used extensively in low Total Dissolved Solids (TDS) brines, such as those found in New Zealand geothermal systems. This has presented several new challenges in the geochemistry of power station processes and materials and also in the interaction of a pH modified brine with reinjection reservoir formations.
The second challenge is the emerging technology associated with the possible utilisation of supercritical fluids present in areas close to magmatic sources. These fluids present unique problems for the geochemist in modelling and then rendering them suitable for use in standard turbines. Experimental work is just beginning for treatment processes for these fluids.

Thermodynamic geochemical data has not always kept up with the use of geothermal fluids of a more “extreme” chemical nature and geochemical modelling is now suffering from a lack of this available data. The basic experimental work required is often hard to justify to science funding providers and worldwide research in this field is limited. It may fall to geothermal power companies to fund this research, just as the thermodynamic data for ore deposit modelling is funded largely by mining companies.

Other geochemical challenges are involved with the microenvironments that can occur in geothermal power stations. Once again, thermodynamic data is often lacking for some of the ‘exotic’ compounds that are formed.