Despite all efforts to promote renewable energies, global demand for crude oil and natural gas has continued unabated. Prices are rising and interest in opening up new sources, including unconventional ones, is rising with them. Methane from coal seams and highly viscous oil at more than 10,000 mPas are already of commercial interest today, but are just as complicated to extract as oil-sand mixtures from the Sudanese desert. Conveying systems must above all be adapted to the media, to the environment and to one another, if production is to be efficient under such conditions.
NETZSCH developed therefore specialised progressing cavity pumps for application in the mid and downstream areas: multiphase progressing cavity pumps. The main characteristic of this technology is that it can also convey highly viscous oils at above 50,000 mPas while maintaining stable pressure. What is more, it can do so with hardly any pulsation or shear forces occurring, thereby avoiding emulsion effects with oil-water mixtures, which would significantly hinder subsequent separation of these mixtures at the surface. This is achieved through the progressing cavity pump’s characteristic conveyance principle. Its conveyance principle is based on a rotor which turns in an oscillating motion within a fixed stator. The geometrical mating means conveying chambers are formed between the rotor and the stator. As the rotor turns in the stator, the medium is transported from the inlet to the discharge side in these chambers.
The robustness of progressing cavity pump technology – along with its lack of sensitivity to the composition of the medium – comes into play both in the mid and downstream area, especially where oils with high contents of other substances have to be transported. Conventional conveying systems quickly reach their limits when consistencies fluctuate, which leads to conveyance failures, pressure loss and material damage. For this reason, costly separators sometimes have to be constructed at every borehole in a field.
The pump manufacturer has developed a multiphase pump precisely for this area of application. This deals with mixtures of oil, water and gas along with sand content and in doing so achieves conveyance rates of up to 1,000m³/h. The tiny shear forces and low pulsation mean hardly any emulsion effects occur during transport, so that complex media can also be conveyed over long distances to collection points. There they can be separated in considerably fewer central separators, which reduces the infrastructure costs for the whole field.
This method is used in the Palogue Oilfield in South Sudan, among others. The gas/oil ratio (GOR) is over 80% with 50 SCFD per barrel mixed with sand. In order to still be able to pump efficiently, 20 multiphase pumps were installed which convey the yield from up to 24 boreholes in each case to the nearest separator – some of them over 15km away. As a protection against sunlight, which can heat the surfaces until they reach a temperature of 70°C, and against the occasional heavy rainfalls, the pumps were fitted with covers and installed on elevated frames. In addition, particularly robust joints were fitted to further increase the running times. In fact, no major maintenance work or component replacement was needed within six years of operation. Stator and mechanical seals had to be replaced on just a few pumps, which had to deal with increased sand content over a long period of time.
The technology has also already proved itself at the other extreme, at a deposit in the Kazakh steppe. In order to cope with the temperature of -40°C which is prevalent there, trace heating was also added to the systems and a double-acting mechanical seal was used instead of a lip seal located on the outside. Furthermore, the oil conveyed on site contains up to 90% gas, which means there was the risk that the seals might run dry and suffer damage. As a protection against this, the pumps were provided with a quench supply to flush the seals.
In addition to the multiphase application, the manufacturer’s pumps are also used for long-distance transport of purified oil, for injecting lubricants or for injecting auxiliary substances in secondary and tertiary extraction. Pressures of up to 250 bar may be reached here. Progressing cavity pumps are also used as transfer pumps with a volumetric accuracy of ±1%. Furthermore, they are employed to empty tanks or oil sumps. For this, the pumps can be installed vertically at depths of up to 12m. These pumps work, for example, on the Shengli Oilfields where an additional collection structure was developed in-house to safely channel away any oil that might leak out via two steel pipes without any risk of clogging.
Because trouble-free, economical operation of a processing line is above all based on the interaction of all the individual modules and components involved, as a systems supplier, the pump manufacturer also offers associated accessories in addition to the various pumps themselves. This starts with basic components such as the motors and control systems, but also applies to special components for the upstream area such as torque anchors, sucker rods and polished rods, along with couplings, through to blowout preventers and gas separators.
Safety valves or bypass systems are also designed and integrated if needed, in the same way as pressure measurement devices or those warning of dry running. Even transport trolleys or base frames can be individually made, perhaps for easier transfer of a mobile rotary lobe pump or for protection against adverse ground conditions. In each case, experts establish the specific design in direct consultation with the customer and taking into account all the operating parameters, in order to achieve the longest and most efficient service life possible for the pumps, in spite of there being difficult media and environmental conditions in most cases.