Industrial Experiences with Downhole Geothermal Line-Shaft Production Pumps in Hostile Environment in the Upper Rhine Valley
Thomas HETTKAMP, Joerg BAUMGAERTNER, Ricardo PAREDES, Guillaume RAVIER, Olivier SEIBEL
[Bestec GmbH, Germany]
The Upper Rhine Valley is a Graben structure in Central Europe, which extends north-south over 300 km from Frankfurt to Basel. The Graben is approximately 50 km wide and is shared by Germany, France and Switzerland. Five geothermal power & heat plants are presently operating within the Upper Rhine Valley, Bruchsal, Soultz, Landau, Insheim and Rittershoffen. Two new projects in Illkirchen and Vendenheim, both close to Strasbourg, are presently drilling demonstrating that there is an economical potential for geothermal in this Graben structure. All projects but Bruchsal produce at temperatures above 135° C, even approaching 170 °C. All of these latter four projects are equipped with an oil lubricated Downhole Geothermal Line-Shaft Pump (LSP) to exploit the geothermal resource. The first oil lubricated Downhole Geothermal LSP in Europe was put in operation in 2007 in Landau, followed in 2012 by Insheim and in 2016 by Soultz and Rittershoffen. In these pumps a lineshafting travels from surface down to the pump stages. It is enclosed in tubing with bearings every 1.524 m. This tubing, the lubestring, is flooded with oil, which once it is used up, is dispersed into the cased wellbore, floats on top of the water level and can be recovered at regular intervals if the annulus of the hot well can be activated to flow artesian. Alternatively, a closed loop lubrication system with an oil return to surface is available, too. The brine produced in all these geothermal plants in the Upper Rheine Valley is quite similar. It is an Na(K,Ca)Cl rich brine with a fairly high content of dissolved gases, mainly CO2. The CO2 content of the produced brines varies between 0.12 to 0.13 in mass percent, therefore the produced brines have to be kept at pressures above the gas break out pressure (GBO) to minimize CO2 corrosion, which is well-known from the Oil and Gas Industry since a long time. Although the oil lubricated Downhole Geothermal LSPs have to survive in such a harsh and corrosive environment, life cycles of more than 4 years for such downhole pumps are not rare. The design of the Downhole Geothermal LSPs has evolved over the years, with greater resistance to wear, deeper settings, higher temperatures, greater pump speed variations and longer pump life. In Europe some important lessons have been learnt since this pump technology was introduced into the geothermal market and the pumps have been (and still continue to be) adapted to the local reservoir conditions. Efforts have been undertaken to tailor the oil lubrication, the quality of the used materials as well as the handling of the long pump bodies. For sensitive environments such as the Molasse reservoir in South Germany, a fully closed loop oil lubrication system has been developed. This oil recovery system has been presented to the Bavarian authorities and is ready for approval. Today these robust Downhole Geothermal LSPs have been installed at depth up to 730 m. A very good overall system efficiency and their high temperature resistance characterize these pumps. Production temperatures exceeding 200 °C are acceptable. Flow rates greater than 180 l/s have been achieved. However, the main advantage of this pump type is, that all sensitive elements such as seals, electrical connections and the motor are on surface, where they can easily be accessed and serviced.
|        Topic: Production Engineering, Steam Gathering Systems||Paper Number: 25024|