During the oil crisis of 1973, we suddenly became aware that fossil fuel resources are limited and will be exhausted soon if new alternatives are not put into use immediately. Conservation measures and extensive research on new sources of energy has eased the demand on fossil fuels, especially crude oil. Geothermal energy as an alternative; source had its share in this devel opment and electricity producing capacity increased from 700 to 4700 MWe during 1970 to 1985. Geothermal reservoir engineering emerged as an impor tant field in the assessment of geothermal sources. During the 25 years of its development, several areas were identified that needed further at tention for the correct description and interpretation of reservoir be havior. This fact as accepted by all operators is vital for the steady and continuous operation of power plants. During this NATO ASI, a detailed review of theory and field case his tories on geothermal reservoir engineering was presented. In understanding .the reservoir, conceptual models, natural state models, well bore measure ments, transient and tracer testing provide data which are indispensable. They are powerful tools in understanding reservoir behavior provided we know how to interpret them. During lectures the theory and practical applications of these interpretive methods were discussed."

Within the last 10 years the world has come to a point where the easily explorable oil deposits have now been found, and it is anticipated that such deposits will be depleted by the beginning of the Twenty-first Century. However, the increasing demand of man kind for energy has caused technologists to look into ways of find ing new sources or to reevaluat: e unconventional sources which, in the past, have not been economical. In this respect, heavy crude and tar sand oils are becoming important in fulfilling the world's energy requirements. What are heavy crude and tar sand oils? There is still some confusion as to their definitions, inasmuch as they vary among organizations and countries. In an effort to set agreed meanings, UNITAR, in a meeting in February 1982 in Venezuela, proposed the following definitions (see also Table 1): 1. Heavy crude oil and tar sand oil are petroleum or petroleum like liquids or semi-solids naturally occurring in porous media. The porous media are sands, sandstone, and carbonate rocks. 2. These oils will be characterized by viscosity and density. Viscosity will be used to define heavy crude oil and tar sand oil, and density (oAPI) will be used when viscosity measurements are not available. 3. Heavy crude oil has a gas-free viscosity of 100-10000 mPa.s (cp) 3 o at reservoir temperatures, or a density of 943 kg/m (20 API) 3 o o to 1000 kg/m (10 API) at 15.6 C and at atmospheric oressure."

During the oil crisis of 1973, we suddenly became aware that fossil fuel resources are limited and will be exhausted soon if new alternatives are not put into use immediately. Conservation measures and extensive research on new sources of energy has eased the demand on fossil fuels, especially crude oil. Geothermal energy as an alternative; source had its share in this devel opment and electricity producing capacity increased from 700 to 4700 MWe during 1970 to 1985. Geothermal reservoir engineering emerged as an impor tant field in the assessment of geothermal sources. During the 25 years of its development, several areas were identified that needed further at tention for the correct description and interpretation of reservoir be havior. This fact as accepted by all operators is vital for the steady and continuous operation of power plants. During this NATO ASI, a detailed review of theory and field case his tories on geothermal reservoir engineering was presented. In understanding .the reservoir, conceptual models, natural state models, well bore measure ments, transient and tracer testing provide data which are indispensable. They are powerful tools in understanding reservoir behavior provided we know how to interpret them. During lectures the theory and practical applications of these interpretive methods were discussed."