Measurements on Fluid-Rock-Interaction of Thermal Water-Inhibitor-Mixtures with the HydRA Facility
Sabine BAUR, Ann-Kathrin NEUBERGER, Dietmar KUHN, Andrea SEIBT
[Karlsruhe Institute of Technology, Germany]
Generally, geothermal water in the reservoir is mostly close to the saturation equilibrium of the included salts. By pumping the water to the surface and extracting the heat, some minerals become supersaturated and precipitate. Therefore scaling occurs within the pipes of the thermal water cycle and in the reservoir at the injection well. The precipitation of supersaturated salts can lead to clogging of the pipes and to blockage of the rock pores or joints. The currently favored approach in the industry is to add complexing agents (inhibitors) to the thermal water before it is reinjected back into the reservoir. The HydRA facility (= hydrothermal reaction apparatus) allows experiments to investigate the interaction of brine with reservoir rock samples under realistic reservoir conditions up to 420 bar and 250 °C. The facility offers the possibility of mixing two undersaturated solutions, which are supersaturated after mixing. In the test section the fluid mixture is pumped through a cylindrical rock specimen (1 inch in diameter, 2 inches in height) to interact with the reactive surface in the pores. Pressure probes at the inlet and outlet of the test section allow the detection of precipitation and dissolution of scales in the pore spaces. Thus, the phenomena during reinjection of thermal water into the reservoir rock can be investigated in the HydRA facility. The topic of this work was to investigate how geothermal water supersaturated with barite (artificially made according to the composition of geothermal water of the Upper Rhine Graben) behaves when it flows through a red sandstone sample. Experiments without the inhibitor DTPMP and with different concentrations of this inhibitor were carried out. Also the stimulation and reactivation of already blocked pore spaces by injecting inhibitor solutions have been investigated. Furthermore the effect of injecting undersaturated water to enhance flow rate and reduce pressure drop in the rock sample was investigated. The experiments show that the performance of a geothermal well possessing a decreased permeability cannot be increased by injecting high inhibitor concentrations. The results show the importance of using inhibitor right from the start when exploiting a geothermal reservoir.
|        Topic: Geochemistry||Paper Number: 14089|