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GEOTHERMAL ENERGY TO SUPPLY DISTRICT HEATING

Ziel

To supply an existing residential area now under renovation, a hospital and a school complex (using a gas-driven heat pump fitted with a recovery system). The geothermal reservoir lies between 600 and 900 m in karstic Jurassic limestone and is already being investigated by a well drilled down to 650 m (well TB1, with 6" screen between 556 and 650 m). After drilling a small-diameter test well (B3) down to 900 m the plan is to sink a large diameter well (B2) down to 900 m in order to tap water. Expected flow-rate is 360 m3/h (B2 + B3), at a temperature of 40 C with a low mineral content. Once the heat has been extracted and the geothermal fluid treated to remove H2S and iron the liquid will serve as drinking water and to refill a body of surface water no longer providing adequate supplies. There are plans (possibly) to deepen well B2 to the Muschelkalk limestone at 1,500 m to prevent possible side-effects on the karst limestone during pumping.
The pumping trial on TB1 and the drilling and piping test in GB3 were very successful.
Total flow-rate is about 300 m3/h at an average temperature of 40 C - the third well GB2 is unproductive and cannot be commercially used as injection well.
The wells TB1-GB3 separated by 400 m have been tested to establish the flow model in the karst and the interaction between the two wells.
GB3 will be used as back-up if some problems occur on the TB1 well.
Trials performed on well TB1 produced the following: final depth - 650 m; karstic limestone Malm reservoir between 610 and 650 m; flow-rate - 114 m3/h; temperature - 42 C for a drawdown of 8 m (pump at the 120 m mark). Well GB3 (7" dia) was sunk to a final depth of 928 m in 1981, completed with 9" 5/8 screens from 550 to 690 m and left as a 6" 1/4 open hole from 720 to 920 m. The karst limestone reservoir lies between 585 and 665 m.
Characteristics are: flow-rate - 180 m3/h; temperature - 39 C; drawdown 28 m (pump at the 150 mark); distance between TB1 and GB3 - 400 m. The third well (GB2), planned as a large-diameter well down to 700 m, was started in the first quarter of 1983. This well is located 2.5 Km distant from GB3 because of influence between the wells TB1 - GB3 during pumping tests. Well GB2 reached the depth of 915 m and tests indicate a possible production rate of 12.5 m3/h at 43 C. This well was obviously not adequate for the aim of the project. A thermal trial (September 83) was carried out between TB1 and GB3, with TB1 producing 20 l/s of which 10 l/s was piped to the thermal baths while the remainder was mixed with an equal volume from the town main and injected into GB3. As no drop in temperature was recorded in TB1 the trial period was extended to 6 months and injection in GB3 was discontinued in April 1984.
Dyes introduced in GB3 and tritium used as tracer in TB1 had been injected to describe the geohydraulic flow model in the karst.

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STADT SAULGAU
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7968 SAULGAU
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