Reinjection is fast becoming an integral part of all modern, sustainable and environmentally friendly geothermal utilization projects. It is an efficient method of waste-water disposal as well as a means to provide additional recharge to geothermal systems. Thus it counteracts production induced pressure drawdown and extracts more thermal energy from reservoir rocks, and increases production capacity in most cases. Reinjection can also mitigate subsidence and be used to maintain important surface activity. Reinjection is, in fact, essential for sustainable utilization of geothermal systems, which are virtually closed and with limited recharge. Reinjection is either applied inside a production reservoir, on the periphery of the reservoir, above or below the main reservoir or outside the main production field. One of the best examples of successful long-term low-temperature reinjection is the utilization of the Dogger formation in the Paris Basin, which started in 1969. Cooling of production wells is one of the problems /obstacles associated with reinjection, even though only a very few examples of actual cold-front breakthrough have been recorded. This danger can be minimised through careful testing and research. Tracer testing, combined with comprehensive interpretation and cooling predictions (reinjection modelling), is probably the most important tool for this purpose. Scaling and corrosion problems can be controlled through different technical solutions, dependent on the particular situation. Finally, a solution has been found for the rapid aquifer clogging, which often accompanies sandstone reinjection. It involves highly efficient filtering and maintaining the whole production/reinjection system completely oxygen-free.
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