The industry wants to embrace new technology, but success comes from balancing this with the overriding need for safety and reliability.
by Steve Digby
August 30, 2016

Reliable pump solutions are a vital part of controlling offshore oil and gas production costs. The difficulties operators experience offshore are what drive developments in pumping technology. Accessing declining reserves in mature fields requires technology that can increase recovery factors and handle higher pressures created by longer umbilical lines. Wider use of floating production, storage and offloading vessels (FPSOs) and the need for more technology to access immobile reserves mean the footprint for pumping solutions is more critical than ever. Because of low oil prices, driving down costs is imperative. Improving oil recovery, pushing the efficiency of solutions and keeping costs down sit alongside a continuing desire for greater assurance of safety and reliability in an industry that has ever more stringent regulations.

Pump manufacturers must possess detailed understanding of the oil and gas industry. The market wants solutions that are proven and that it can rely on, but it also needs innovation to meet the challenges it faces today and into the future.

Two-screw pumpImage 2. A two-screw pump

A Need for Change

Submersible pumps are a critical part of oil recovery in artificial lift applications. Their performance and reliability are directly related to the operational efficiency and profitability of a field. Because they are subsea, sometimes below the Christmas tree, failures can result in significant lost production and intervention costs. Historically, such pumps have been based on electric motors, but it is the electrical components that are at the highest risk of failure. Changing these pumps to a hydraulic design can significantly increase reliability. Indeed, this technology has shown that it offers a mean time to failure (MTTF) of 12 years, typically three to four times greater than equivalent electric alternatives.

So why is the hydraulic submersible pump (HSP) so reliable? The design of the HSP removes the most common failure modes of the equivalent electric submersible pump (ESP) as it has no subsurface electrical componentry. It also offers a much shorter length with the pump end and hydraulic turbine both mounted on a single shaft. This more compact design increases rotor dynamic stability and simplifies installation, because there are fewer connections and no need for an electrical umbilical or coupling on-site. The risk of damage while the pump is being deployed is also greatly reduced, particularly in wells that include a large dogleg severity (DLS). Power fluid, commonly supplied from the topside, not only serves to drive the pump but also is used to maintain an innovative hydraulic balancing system and hydrostatic bearing setup, removing the maintenance needs created by rubbing bearings and seals.

Pump reliability and performance can be further enhanced with a HSP, as units can handle 75 percent continuous gas content and 100 percent gas slugs, reducing the risks of damage from gas lock. As a constant-power, hydraulic machine, the HSP attempts to draw the same amount of power when the produced fluid density changes with varying gas content, automatically speeding up or slowing down. If, therefore, there is an increase in the amount of gas in the flow, the HSP avoids gas locking as it increases speed and rapidly pushes gas through the machine in a fraction of a second. This makes the pump resilient to changing well conditions and less prone to failure.

Industry-Standard Designs

Many pump applications in the oil and gas industry use pumps that were designed more than 40 years ago. Unlike the example with the HSP, these pumps have not changed because they are proven to be reliable and are strong workhorses for the industry—simply meeting the needs of their pumping duty. One such example is the triple screw pump that gives quiet, pulse-free operation ideal for forced lubrication systems. The design has not changed over the years because these pumps already offer reliability with high efficiency. They remain a compact, space-saving solution that delivers a constant, stable flow with low noise that is ideal for the application.

Of course, pump designs that have set the standard in the industry are supported by vendors that can meet specific requirements, ­such as ensuring that all standards and test requirements are met and correct documentation packages produced, as well as producing complete packaged systems with all associated instrumentation and connections to exact specifications.

Improving Proven Designs

There is a middle road between new designs that are on track to be proven and older, trusted technology. Pump manufacturers can also use proven technology to create new, innovative solutions that address specific challenges.

When handling hazardous chemicals, hydraulically operated double-diaphragm pumps give the advantage of a safe, leak-free solution with reliable, accurate operation. Once set to the required flow rate, no further adjustments are necessary. This technology also gives metering accuracies of up to ±0.5 percent with the ability to pump against high pipeline pressures, making this pump ideal to ensure that the correct ratios are maintained in chemical injection applications. The excellent accuracy of this pump further optimizes the use of expensive chemicals, saving operational costs while ensuring that quality is maintained with correct dosages used.

Hydraulic diaphragm pumps also can be easily controllable between 0 and 100 percent flow while maintaining accuracy. This gives flexibility to vary the amount of liquid being pumped to suit changing process needs. The variation can be achieved by either adjusting the pump speed, stroke length or a combination of both. Using either an actuator for stroke length or frequency inverter for speed, the pump can be controlled using all-modern communications protocols, ensuring total operational flexibility and efficiency.

Pump reliability can be further enhanced with the use of either periodic at-line or continuous online monitoring software. This can be used as a stand-alone solution or incorporated into an asset management system to enable advanced detection of possible pump failure and to facilitate predictive maintenance. Use of such solutions can help optimize maintenance schedules, maximize uptime and protect production capacity.

Double Diaphragm PumpImage 3. A double acting double diaphragm pump

To save space and installation costs offshore, some hydraulically operated double-diaphragm pumps use the well-proven hydraulic diaphragm pump head in innovative ways. One metering pump uses one double-acting pump head. The double-acting head reduces weight and footprint by about 20 percent compared with two single-acting diaphragm pump heads. One process pump again uses the hydraulic diaphragm pump head technology, but this time reduces the required footprint for installation by cleverly arranging triple pump heads in three dimensions. These are just some examples of how innovation can be applied to proven technology.

Many pump suppliers offer additional equipment within their product portfolios that can enhance pump performance, such as efficient filter solutions to protect pumps from the damage debris can cause.

When offering multiple technologies, suppliers have the experience to ensure the best ancillary equipment is selected to optimize pump performance, and this may not always be the most expensive option.

A complete, integrated pump package from a single supplier may, therefore, offer the most cost-beneficial solution while providing the peace of mind of assured performance.

Conclusion

By understanding the needs of the oil industry, pump manufacturers can decide where to invest in areas of development that improve operating viability and profit.

As technology advances, more challenging processes, such as deeper wells and higher pressures, become viable. The industry wants—and sometimes needs—to embrace new technology to secure its future, but success comes from balancing this with the overriding need for safety and reliability.

Whether new technology needs to be developed, proven technology enhanced to deliver greater benefit, or older, trusted technology simply well-applied for the given application, trusted pump solutions are a vital component in helping to ensure smooth, reliable offshore operations.