PURPOSE:To simplify the captioned work by replacing muddy water with fresh water at the completion of excavation by means of mud drilling, pushing down the fresh water level by using two-phase gas consisting of geothermal steam and hot water, which was press-introduced from a pit entrance, holding this state for a certain time, and removing the two-phase gas. CONSTITUTION:At the completion of excavation work to a geothermal well, muddy water is replaced with fresh water, thereby cleaning the inside of a pit. Next, two-phase gas consisting of geothermal steam and hot water, both of which are blowing out of an existing geothermal well, is introduced by pressure into the pit toward its bottom in order to push down the fresh water level, and this state is held as it is for a certain time. After heating the entire water column, which has been pushed down, up to the boiling temperature or higher, the high pressure acting on the pit entrance is relieved. Then, both a flow toward the pit entrance and a bumping phenomenon are caused to the water column, thereby inducing a rise in the underground pressure in order to achieve the initial steam blowing. Accordingly, the captioned work can be simplified.
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