Optimizing wellhead gas compression systems

With continued low natural gas prices, operators with low-volume wells in mature fields face the constant challenge of maintaining production while controlling costs. Declining bottomhole pressure and the accumulation of water in older gas wells can reduce production rates, making fields uneconomical. High cost and unreliable screw-type wellhead compression systems can fall short of providing profitable solutions.

This dilemma for operators presents an opportunity for compressor manufacturers to provide wellhead compressor systems developed specifically to boost gas from wells with the capacity to produce 0.2 million cubic feet per day (mmcf/day) to 1.4 mmcf/day. Because of low commodity prices, these wellhead compressors need to have relatively low capital or lease costs and operate reliably more than 95 percent of the time.

Reliability reduces costs

One compressor manufacturer, Sertco Industries, designs and manufactures small reciprocating compressors to boost gas well production, separate water from the gas stream and inject the dry gas into the sales line. These custom-designed one- and two-stage portable systems have operated reliably in mature gas fields globally. To make good on the company’s promise of 98 percent uptime and a 12-month, no-fault warranty, reliable, cost-competitive components are necessary for the compressors. Over the past few years, engineers have reduced system cost and increased operating reliability by evaluating and selecting the right valves and control components for their compressors.

The compressor manufacturer partnered with a major valve and control solutions provider for components for handling gas and liquid entering and exiting the compressor. As gas and liquid come into the compressor from the wellhead, a liquid level control device prevents excessive water from building up in the system. Pressure regulators can control valves and direct gas to fuel the compressor and assure that gas leaving the compressor enters the sales line at a constant pressure. Some of the components selected were pneumatic liquid level controllers and gas pressure regulators.

Short lead times for components reduced the manufacturer’s inventory requirements for spare parts. In operation, the components have proven to be more reliable than more expensive alternatives, maximizing uptime and minimizing total cost (see Table 1).

Norriseal-Wellmark components used on Sertco compressors   Component type Application Advantages Pneumatic liquid level controller Dump valve actuator on suction scrubber

• Reliability
• Long-term performance

Pneumatic liquid level controller Dump valve actuator on more complex suction scrubbers

• Performance
• Solved problem with faulty reset switches
• Availability

Gas pressure regulator Regulates discharge pressure down to 35 psi to serve as instrument gas supply for pneumatic valves and systems

• Performance
• Maintains constant output at higher pressures
• Availability

Gas pressure regulatorRegulates gas pressure and volume.
Also used as a suction recycle system regulator

• Performance
• Delivery

Gas pressure regulator High discharge pressure recycle system regulator

• Performance

Safety relief valvePop-off safety valve

• Performance
• Reliable threads
• Durable stainless internals

Table 1. Components used on Sertco compressors

The combination of reliable products, quick delivery times, competitive pricing and responsive technical support have benefited the compressor manufacturer. Because of quality manufacturing and quality assurance/quality control programs, it no longer needs to rework supplied components, a frequent problem in the past. Better component reliability has resulted in a drastic reduction in service calls, which have an average cost of $675 each, resulting in substantial savings (on compressors under warranty) or for the end user (on compressors out of warranty).

The components operate reliably in all of the manufacturer’s compressor systems, which are deployed in the U.S., Latin America, Europe, the Middle East and Indonesia.