Jascha Kolter on taking established pump technology 10,000ft deep
In the current era of technology advances in offshore oil and gas field developments, most of these advancements are concentrated toward greater hydrocarbon recovery and efficiency of the overall field design to reduce CAPEX or OPEX. One such new technology is the transfer of well treatment chemical storage and pumping equipment from the host production facility to the sea floor, adjacent to the wells. The significant advantage is that it allows for the reduction of complex production umbilicals and assists in supporting all-electric subsea trees by moving the chemical injection systems subsea.
Hammelmann has built chemical pumping systems for major operators’ production facilities around the world for many years. With the idea of moving this technology subsea, and with support from major operators, the firm developed its high capability and reliability pump into a subsea package.
These high-pressure pumping systems are novel in that they use a labyrinth metal to metal, plunger to bore sealing system. This allows the pumps to operate at extremely high pressures and flow rates, while also universally working with almost all difficult-to-pump clean fluids. The challenge was to reliably transfer this system into a subsea package that could meet the stringent operational requirements needed for deep water operation.
A team of Hammelmann’s experienced engineers took on the challenge by working to meet or even exceed all the fundamental needs. The first challenge was picking the right size and configuration pumps to offer. Two of their highest priority goals were to meet high reliability and high-pressure multiple fluid flow rate and type compatibility. When the company was approached for this technology, the goal was to provide the high level of reliability, flexibility and safety established in its surface pump programmes and transfer these traits into a very capable subsea package, intended for a wide range of subsea applications.
The team’s configuration of variable displacement and an all-Tungsten carbide plunger and bore were selected. The next challenge was packaging this system so that external subsea pressure could be managed, and internal components could use materials better selected for their operation and their compatibility with subsea. The company decided to place its pump and supporting components inside an outer housing that could ensure compensation to suction pressures while keeping the pump safe from external pressure transients while idle or pumping. This had the added benefit of isolating other components such as the drive motor from sea water and sharing a common lubrication system with all components.
Hurdles to Overcome
Operational challenges of placing the pumps long distances from the production facilities meant the pump needed to be capable of operating with initial voltage losses and against full injection pressure head. To accomplish this, the drive motor is capable of handling large voltage drops, and the pump is internally configured and capable to de-stroke to zero flow output, start, then bring on flow gradually against pressure. In addition, it is a very capable high-pressure and high-volume pump. By exchanging plungers and heads, the same pump with smaller plungers can be used in HPHT applications over 1,380 bar (20kpsi), or with large plungers for high volume flow.
The initial pump is complete and has passed comprehensive tank testing at Hammelmann. As work progresses, the German manufacturer is as confident in its subsea pump as it is in its established high-pressure pumps. The use of a full enclosure allowed the firm to use the best and most reliable materials and components available, so as the pump wears, it wears slowly while providing exceptional longevity, long service intervals and an overall long lifespan. As the company initially intended the design to be used for chemical injection, enquiries for other applications occurred, for example as a lube oil pump for production booster pumps, or for other injection such as production enhancement chemicals.
In most of these field design ideas, chemicals are stored in tanks subsea, but in high-flow constant injection applications, only a surge tank is needed, such that chemical supply can then be provided with a much lower cost low pressure field supply line.
Jascha Kolter is with Hammelmann