| Abstract |
Sustainable development involves meeting the needs of the present without compromising the ability of future generations to meet their own needs. At the core of this issue is the utilization of the various natural resources, including the worlds' energy resources. Geothermal resources have the potential of contributing significantly to sustainable energy use in many parts of the world. The terms renewable and sustainable are often mixed up. The former concerns the nature of a resource while the latter applies to how a resource is utilized. In many cases several decades of experience have shown that by maintaining production below a certain limit a geothermal system reaches a kind of balance that may be maintained for a long time. A definition is reviewed, which argues that sustainable geothermal utilization involves utilization at a rate, which may be maintained for a very long time (100-300 years). Examples are also available where production has been so great that equilibrium was not attained. Such overexploitation mostly occurs because of poor understanding, due to inadequate monitoring, and when many users utilize the same resource without common management. Three case studies are presented where reservoir modeling is used to analyze sustainable management of the corresponding resources. One of these involves a small low-temperature geothermal system in Iceland, where modeling based on long-term monitoring has been employed to estimate the sustainable potential of the system. Another involves the geothermal resources in a deep sedimentary basin in the P.R. of China. This second resource is of an entirely different nature, and requires full reinjection for sustainable utilization. The third case study involves a high-temperature geothermal system in Iceland, which is utilized for combined thermal energy and electricity production. Modeling indicates that the current rate of utilization can't be maintained in a sustainable manner for 100-300 years. The impact appears to be reversible, however, and the field may likely be utilized at a reduced rate, in a sustainable manner, following a 30-year period of excessive utilization. |