Scenario: A hot -dry geothermal project is being planned in the vicinity of some

Question

Scenario: A hot -dry geothermal project is being planned in the vicinity of somewhere, CO> Below is a simplified map of the area indicating the proposed location of the injection well. The principle of a hot- dry geothermal energy project is to drill an injection well into an impermeable formation and hydro fracture the rock to creat a localized fracture field that, when water is pumped into it, this water will not esccape the facture field. As long as the local geothermal gradient is sufficient to heat the water to boiling in the fracture field the stream produced can be recovered through nearby production wells to drive a turbine generator. the average geothermal gradient within the map area is 41 degree celcius per kilometer of depth. Use 12 degree as the average temperature at the surface.

The rock type underlying the area as a following

A: Granite B Sandstone C Interbedded sand stone and mudstone D: Basalt flow

C3) What will the temperature be at the bottom of the injection well? Given this temperature, do you expect this geothermal project to succeed in generating electricity?

Explanation / Answer

Answer C:The injection well is drilled into the impermeable formation so that when the rock is hydrofractured the water will not escape from the localised fractures and the stream produced from the boiling water can be recovered and this steam is then used to drive the turbine. So the rock type will be interbedded sandstone and mudstone since the sand has a high porosity and is a good reservoir rock for oil and gas whereas mud is an impermeable formation which seals the rock and prevents escape of gas from the reservoir rock and thus are useful as stratigraphic traps.

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