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

C1) Which geologic formation does the injection well neeed to be drill into? Explain why?

Explanation / Answer

Geothermal springs are heated groundwater sources from where the hot water rises from the earth crust to surface. These hot springs are used to generate electricity and supply to domestic purposes in cold areas. The hot mantle or heat from sliding fault zones or reaction of sulphides produces heat in geothermal springs. In active volcanic zones water is heated at magma contact (molten rock) rises to surface as hot springs.

Here the rocks given shows that the sediments overlying on basalt volcanic flow which in turn intruded into batholithic granite. So it shows that top layers are sandstones and interceded sandstones and mudstones. The basement is granite. Basalt seems to be intruded into sediments. The basalt with hot mantle magma heating groundwater and rising to the surface.

So basalt flow is the source for hot spring so we have drill upto basalt to pump water to turbines to produce electricity.

It can also be drilled up to mudstone, if it is very thick and impermeable. The impermeable mudstone not allow hot water to eascepe from their place so drilling borehole upto mudstone above basalt flow also serve the purpose.

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