Permanent Monitoring of Dynamic Fluid Levels
Progressing cavity pump with underground drive supplies pressure and temperature
A specially designed progressing cavity pump with underground drive increases the production efficiency of an oil-water mixture while reducing costs and resources.
Furthermore the PCP system enables the permanent monitoring of dynamic fluid levels from the depth of the well.
Look behind the scenes
Until the end of 2019, Neptune Energy Deutschland GmbH used the gas lift principle to pump an oil–water mixture with a high gas content to the surface at one of its sites on the Bramberge oil field in the German Emsland region. While the tried-and-tested process is still widely used due to its reliability, it is energy-intensive and therefore expensive. “At the Bramberge oil field, oil has been pumped for decades using the gas lift principle,” explains Jörg Eitler, Head of the Global Business Field Oil & Gas Upstream at NETZSCH Pumps & Systems. “Associated gas is pressed into the standpipe of the well under high pressure, pushing the oil–water column to the surface.” This reliable process was also used in the Neptune Energy well until the end of 2019. But this type of oil production has one crucial disadvantage: It requires a lot of energy and therefore has poor efficiency.
To optimize the efficiency of oil production on site, the management at Neptune Energy consequently decided to change the pumping technology. They chose a progressing cavity pump with underground drive – an electric submersible PCP system – from NETZSCH Pumps & Systems in Waldkraiburg, Germany, which can be configured for low flow rates and a high free gas content. “Our challenge was to offer a technical solution which is equally reliable as the gas lift process but highly flexible at the same time,” explains Eitler. “It should be possible to adapt the system to the changing conditions – even when installed directly in the well.” In addition, the new system should ensure a pressure of 10 bar at the surface. The operating company also needed reliable pressure and temperature data from a depth of around 1,000 m in the well. Based on the requirements profile with a low flow rate, changing pumping conditions including a high free gas content and the need for continuous application information, NETZSCH suggested an ESPCP system with a downhole sensor system.
The special feature of this pump is that the rotor is not driven by an above-ground drive head using a very long shaft or rods but that instead the conveying elements and the motor are sunk into the well. „The motor and the bearing unit are connected directly to the rotor with a flexible rod. All radial and axial forces of the rotor are absorbed by a special underground bearing housing“, explains Eitler. „In addition, the dynamic seal is also located in the well.“ This excludes environmental impact by leaks above ground. The extreme flexibility for different application conditions had to be taken into account for the configuration of the pump; this means that motor cooling has to be ensured even at a very low flow rate or with a very high free gas content. As there was no reliable information on the pump intake pressure (dynamic fluid level), a very high safety factor was specified for the pressure capacity of the pump (rotor–stator combination). „A sufficient level of material strength was taken into account for this unit in particular, which is equipped with a rotor with a small diameter and features a low flow rate,” continues Eitler. In addition to this, the pump system was equipped with a full downhole sensor system. It includes pressure, temperature and vibration sensors and supplies data on the pressure at the pump – which can be used to draw conclusions on the dynamic fluid level in the well, data on the temperature at the pump and vibration data, which are important for early detection of faults. The signals are sent to the surface through the existing power cable and used for the central controller.
The ESPCP pump system was installed at a depth of approx. 1000 m and commissioned in mid-November 2019. It has since been running to the full satisfaction of the oil field operator. With the special frequency control, the system – which delivery around 9 m³ of oil per day – can be adapted to the actual operating conditions underground. In addition, the free gas never created a gas lock, i.e. a blockage inside the pump. The high efficiency of the system additionally achieved significant energy savings. “This use of the ESPCP represents a milestone in the field of oil production technology”, explains Eitler. Reducing the energy consumption not only achieved a significant cost optimization, the system is also an important step towards the digitalization of oil fields: “For marginal wells/fields in particular, information about the pressure in the well through continuous monitoring of the dynamic fluid level is the key to successfully running the fields. Especially when the oil price on the global market is low, this information can be a crucial criterion for the continued operation of highly watered-out fields. This is oil production 4.0”, summarizes Eitler.
Medium: Oil-water mixture with gas content up to more than 90 %
Throughput volume: About 9 m³ oil per day
Pressure: 10 bar at the surface
Rotation speed: 100 - 500 rpm
Operating depth: Approx. 1,000 metres below the surface