PURPOSE: To efficiently extract heat from cracks of a plurality of layers and inject water in a proper quantitie into each crack of the layers formed in one well, wherein the cracks are formed at different depths. ;CONSTITUTION: In a multistage water injection device for use in high temperature rock body power generation wherein water is injected into cracks 8, 8 of multistage formed in a bore 3 excavated in a high temperature rock bed 16 deep underground to obtain steam for power generation, a water injection pipe 5 is inserted into the bore 3 to form a double-pipe construction comprising the wall of the bore 3 and the pipe 5. Distribution holes 7, 7 with dimensions in proportion to the amount of water to be fed into a crack 8 at each stage are provided at locations corresponding to each crack of the layers. For example, the dimensions of the holes 7, 7 are determined in such a manner that distribution holes 7, 7 corresponding to a crack through which water is passed in larger quantities than through a crack through which water is passed in least quantities are made smaller on the basis of the crack through which water flows in least quantity to throttle a water passage so that the amount of water flowing through a crack through which water flows easily is made equal to the amount of water flowing through a crack through which water flows less easily.;COPYRIGHT: (C)1994,JPO&Japio
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