The estimation of rock age (Fig.7-1) is done with the following purposes:
(A) Assessment of the heat source location
The location of the igneous rocks playing the role of heat source for the geothermal system is estimated assisted with the results of rock age determination studies (K-Ar method, Fission Track method <F.T.> or Thermo-Luminescence method <T.L.>).
(B) History of a geothermal active area.
Using the T.L. method it is possible to estimate how the most active part of the geothermal area migrates (Fig.7-2).
(C) Confirmation of the stratigraphy.
The stratigraphy of disclosed by the well geology is confirmed by rock dating data of each geological formation.
The K-Ar and F.T. methods are mature techniques. Apart of these methods it is necessary to develop a technique that can determine rapidly the age of young alteration in rocks in order to select the promising area within a geothermal field where to drill production wells. For this purpose, West JEC, in collaboration with NEDO, have developed and successfully applied the alteration rock dating technique using T.L. (Fig.7-3)


Click to image
Fig.7-1 Comparison of each rock dating methods
Fig.7-2 Thermoluminescence (TL)
measurement equipment
Fig.7-3 Conceptual model of the Akinomiya and Wasabizawa geothermal area

 

 

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