Matters of principle are considered connected with thermal energy extraction from
dry rocks by creation of a heat exchanger in a vertical well. Construction of the
heat exchanger is suggested, consisting of a string of pipes concentric within a
casing. The cold water injecting through annulus to the bottom hole is heated and
then lifted through thermo-insulated string up to surface pipelines for consuming.
The simple engineering design of temperature for obtained heated water is given and
influence of the basic parameters of the problem is analyzed. Some nuances and errors
of approximated solutions are considered including the correction on eccentricity of
lifting and casing strings arrangement; the estimation of recoverability of thermal
regime of rocks when working the heat exchanger only in winter months is suggested.
Different practices of exploitation and modification of construction of down-hole
heat exchanger are studied for improvement its operations efficiency. The questions
are touched connected with calculations of thermal energy extraction of geothermal
field with application of circulating system, which foresees back injection of water
into bed for maintenance of strata pressure. The simplest formulae for estimation of
natural heating of water injected along the borehole of injection well are
represented. The analogical results are given for propagation of temperature
disturbances in rocks, in roof and bottom of formation, on exhaust of thermal
potential of thin and thick beds in due course. Lifting of water through the borehole
is connected with heat losses, i.e. in well bore the hot water gives a portion of
heat to rock. The experience is used widely, accumulated by oilmen on non-isothermal
water displacement of oil.

A number of technologies of binary GeoPP with down-hole heat exchangers are
elaborated. Investigations are carried out on optimization of thermodynamical Rankine
cycle and it is established that for binary GeoPP there is the optimal temperature of
working agent evaporation, which depends on temperature of thermal water, the least
temperature head in evaporator and temperature of condensation.

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