Look behind the scenes
Around 30 years ago, an energy supplier in Hannover had started to use an underground deposit for gas storage. After a few years, however, it became evident during pumping of the medium that the geological horizon in which it was stored had emitted substantial oil quantities into the gas. For economic reasons this resulted in a conversion from gas to oil production. A suitable pump system had to be acquired in order to reliably transport the crude oil to the surface from a depth of more than 1,200 m.
The extreme conditions on site, however, presented very high requirements for the pump design: as the medium was a multi-phase mixture with a very high gas content, the usual centrifugal pumps with underground drive were not an option. With a very high free gas content, this type of pump always presents the risk that all impellers fill up with gas and the entire system becomes unable to generate pressure. The alternative progressing cavity pump (PCP) technology is therefore normally used for the draining of gas wells, for example. All pumps of this type used in Central Europe until now, however, have been PCP systems with above-ground drive. These units have a dynamic seal on the surface which in case of extreme pressure can become overloaded and trigger a blowout.
To exclude the possibility of overloading the dynamic seal on the surface and therefore a blowout, NETZSCH suggested the use of the first progressing cavity pump which is driven underground in Central Europe – the NETZSCH ESPCP. The special feature of this pump is that the rotor is not driven via a very long shaft or linkage from a drive head on the surface, but rather the rotor-stator combination and the motor are sunk into the well. The motor or bearing unit is connected directly to the rotor via a flexible rod. All radial and axial forces of the rotor are absorbed by a special underground bearing housing. In addition to this, the dynamic seal is also located in the 1,200 m deep well. This moved all critical components of the pumping solution below ground, precluding environmental impact from leaks above ground. The motor for the system is a permanent magnet model (PMM) with special SPMM control which can ensure flexible flow rates, even with extreme fluctuations of up to 500 percent . Thanks to the PMM motor and the precisely adapted SPSS control, the solution designed by NETZSCH reliably achieves speeds from 100 to 500 rpm. That can ensure the desired flow rate of 1:5 and therefore achieve maximum flexibility.