Geothermal - Wellhead temperature drop

[GeminiII]

Hi,
I need help for an economic evaluation of a geothermal problem. I'd like to know if, in your experience, the temperature of water at wellhead point could be considered close to the bottom temperature of the well (or with difference < 1 °C). The well is 1500-2000 m, the bottom temperature is about 80-90°C, pressure 3-4 bar.
Thanks

 

[racookpe1978]

First, assume constant flow, or near-constant. for an economic analysis, you're not examining transient cases, right?

After a few hours of flow, the water temp at bottom will have heated the pipe, heated the rock around the pipe, and heated the insulation and grout topside, right? So, there will be very little added loss to that "static" loss of heat energy of the entering water through the pipe to the surrounding rock.

But 2000 meters of pipe closely surrounded by rock with no insulation between pipe and rock will reduce water temperature at top of pipe measureably. The cold rock will approach a near-infinite heat sink, so you will always lose some heat.

 

[EdStainless]

If the water is coming up a production pipe that is inside a cased well then you will get hotter water, just a few degrees below bottom hole temp. If it coming up the well bore, then as Racookpe said, you have an infinite heat sink.

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P.E. Metallurgy, Plymouth Tube

 

[GeminiII]

Thanks!

The production pipe is inside a concentric casing system. I need only simply model for MS Excel to do a rough approximation of the temperature drop between bottom-well and wellhead and I thought to use a multilayer cylinder-conduction model.

 

[KevinNZ]

With no thermal loss to the formation the temperature will increase just from the change in pressure.

From steam tables. A 2000m and 80c the h = 350.82 kJ/kg, At 3 bar that h gives a temperature closer to 85c.