Assessment And Modelling Of Geothermal Reservoirs (Small Utilization Schemes)

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Journal Article: Assessment And Modelling Of Geothermal Reservoirs (Small Utilization Schemes)

Geothermal reservoirs are characterized by their fluid chemistry, natural heat loss and reservoir structure. A revised classification of low (<125°C), intermediate (125-225°C), and high (>225°C) temperature reservoirs has been given. Almost all types of geothermal reservoirs can be used for small plant development. Three different approaches have been used for assessment of geothermal reservoirs, namely: (a) assessment of gross power potential (volume approach), (2) assessment of productivity of wells and, (3) assessment of productivity potential by computer modelling. Assessment of reservoirs to be developed for small plants is restricted in that it can only be based on data of a few exploration wells; such assessment has to occur at the end of the exploration drilling phase. Power potential estimates are of limited use for adequate reservoir assessment since the permeability structure of the reservoir is neglected. Productivity assessments of exploratory wells can explain the behaviour of wells but do not allow an assessment of any major part of the reservoir. A gross permeability structure of convective reservoirs, however, can be obtained by modelling the reservoir in its natural state. The model can be used to predict the reservoir response for various utilization schemes with different fluid production characteristics. The predicted productivity potential depends therefore both on the permeability structure of the reservoir and fluid production parameters. Numerous examples (mainly from developing countries) have been cited which show that assessment of productivity potential can be extended to most types of geothermal reservoirs. Although reservoir assessment by modelling appears to be a generally suitable method, it requires access to large computers and is time consuming. Its predictive power is limited by equivalence problems and poor input models, but the same problems also affect other assessments. Poor input models are usually the result of poor exploration models which, in turn, are often caused by misidentification of reservoir type and of secondary reservoirs (concealed outflow structures).

Manfred P. Hochstein

Published Journal 
Geothermics, 1988



Manfred P. Hochstein. 1988. Assessment And Modelling Of Geothermal Reservoirs (Small Utilization Schemes). Geothermics. (!) .