| Abstract |
A number of long and well documented utilization and response case histories of hydrothermal systems are available worldwide, many spanning more than 30 years. These are extremely valuable for studying the long-term response and hence production capacity of geothermal resources, as well as their renewability and possible sustainable utilization. Simple evaluations, and associated calculations, for a few low-temperature (< 150°C) case histories presented, demonstrate this. The cases histories reveal that the associated geothermal systems can often be classified as either open or closed as regards production induced recharge. Fluid volumes extracted over several decades range from being much less to being approximately equal to the estimated pore volumes of the reservoirs in question. This may explain why significant chemical changes haven’t been observed in the cases presented. In addition volume estimates based on long-term pressure changes are often very large compared to the estimated volumes of the hot reservoirs. A slow pressure decline for many closed systems and a slow cooling of many open systems demonstrate their potential sustainable utilization. |