| Abstract |
A hydraulic stimulation was conducted in well GPK-2, at Soultz-sous-ForÍts (France), in July 2000, one year after its deepening from a depth of 3,500 m to 5,100 m. During this operation, two organic tracers (Na-benzoate and 1,5-naphthalene disulfonate) were continuously injected at a controlled concentration of about 2 mg/l into GPK-2 with around 26,800 m 3 of fresh water. The chemical composition of this water is very different from that of the geothermal brine (NaCl fluid with a TDS close to 100 g/l). Four short-term production tests were carried out between December 2000 and April 2002. The fluid produced from GPK-2 was geochemically monitored during these tests. This paper presents the main results of that fluid monitoring. Comparison with natural tracers such as chloride indicated that the organic tracers were remarkably stable during more than 2 years at around 200?C. At each production test, the mass proportions of injected fresh water and geothermal brine could be estimated; the recovered fresh water could also be calculated (less than 7% relative to the total volume of fresh water injected into GPK-2). It was observed that the injected fresh water was internally replaced by the geothermal brine in the reservoir. The mean flow rate of the geothermal brine circulation could be estimated at 1-1.2 m 3 /h. Between January and March 2003, and during another operation of hydraulic stimulation, a third tracer (2,7-naphthalene disulfonate) was injected into GPK-2 at a controlled concentration of about 3 mg/l, with about 24,000 m 3 of fresh water. The detection of 1,5-nds, almost 3 years after its injection into GPK-2, and that of 2,7-nds in the fluid discharged from GPK-3, have shown that the recently drilled GPK-3 well (depth of 5,100 m) is directly connected to GPK-2. |