Control Valves: Aid Natural Gas Production

A Canadian oil and gas company operates numerous oil and natural gas wells in remote areas of northwestern Canada.

Producing Gas Wells

Each gas well is equipped with a metering skid that controls output from the well. The skid contains a primary throttling valve, isolation valves, metering equipment and remote telemetry to enable the skid to connect to the master SCADA system. The primary function of the metering skid is to control both the amount of flow and the pressure of the well in order to control the drawdown on the well and achieve maximum production.

The natural gas extracted from the wells contains a high volume of water and sand moving at relatively high velocities that would quickly erode metal surfaces. The company had standardized on V-ball valves but was experiencing a range of problems. The most severe were catastrophic valve failures that would allow the entire skid to fill with sand. This would require a replacement unit at a cost of $150,000-$200,000.

The entire V-ball valve experiences severe wear caused by sand in the gas. Replacing the valves required a shutdown of the well at a loss of 125,000 cubic feet of gas. A six-hour shutdown results in a $6,250 loss in revenue.

Reducing Wear & Tear

Red Valve's district sales office in Vancouver worked with the company to find a solution to the wear problem while maintaining or even improving control of the well. The V-ball valves were replaced with its Series 9000 high pressure control pinch valve. This is an ANSI 300# Class Valve available with pressure ratings to 720 psi. Like all Red Valve pinch valves, it features a full-port opening with no obstructions and no changes in the direction of flow. The elastomer pinch sleeve is very resilient, allowing it to absorb the impact of the sand without wearing.

For installation in the metering skids, the new valves were equipped with hydraulic actuators and Fisher® smart positioners from Emerson Process Management to allow them to be tied into the existing SCADA control system. The valves were also equipped with the latest “smart” sleeve technology that senses wear in the sleeve and signals the SCADA system to schedule a replacement. Several manually actuated isolation valves, equipped with bevel-gear operators, were also supplied.

Maximizing Production
In an effort to maximize production without killing the well, the oil and gas company often kept these control valves throttled at 40-50% closed. The mixture of sand and water could travel as fast as 150 feet per second, or 100 miles per hour. This highly abrasive mixture would quickly wear out the seats, seals and even bodies of metal V-ball valves.

The Red Valve high pressure control valve was retrofitted to increase the service life of the valve and maintain tighter control. Fuel gas was used to actuate the pneumatic cylinders, and the valves were controlled by low-voltage solenoids operating on solar power.

The valves were in operation for one year with no loss in performance or maintenance required and, upon routine inspection, showed no significant signs of wear.

Conclusion

Field gas captured from the wells is piped to a central location where the sand and water can be removed. An inlet separator is used to allow the sand and water to settle out and the gas to rise. The gas collects in the top of the separator where it's pulled off by means of a gas compressor, while the collected sand and water are dumped off to a produced water tank. A control valve is used to precisely modulate the amount of water that's drawn off to ensure the level doesn't rise too high and enter the compressor inlet.