Current State of Development of Deep Geothermal Resources in the World and Implications to the Future

Abstract

This paper summarizes a part of the results of Subtask (A) ìExploration Technology and Reservoir Engineeringî in the IEA Task ìDeep Geothermal Resourcesî. Deep geothermal resources were here defined as geothermal resources at a depth greater than 2500 meters considering availability of the worldwide information. Primarily, we review a current state of development of deep geothermal resources in the world based on the information obtained through the Task excursions and literatures. It is no doubt that development of shallow geothermal resources is more economical than that of deep geothermal resources. Nevertheless, deep geothermal drillings have actually been made in the world for the various reasons: to overcome the development site restriction, to expand the capacity of existing shallow reservoir, to compensate the pressure decline in existing shallow reservoir and to discover large-scale reservoirs. We shall refer to examples in Kakkonda, Palinpinon, The Geysers, Larderello, Ohaaki, Dexie Valley, Salton Sea and Cerro Prieto. Secondly, we discuss general factors controlling deep geothermal systems. These factors are the tectonic regimes, depth of heat sources and brittle-plastic transition.