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SAFETY AT THE WELL—API 6A

 

The Christmas tree, ESD/PSD and other equipment in a shale field are subject to many factors that impact the type of valve and automation solution. For example, the Bakken wells generally produce 1,000 to 3,000 barrels per day (bpd) at pressures of 2,000 to 4,000 psig, with temperatures averaging below 200°F (93°C). By comparison, the Eagle Ford wells can produce as high as 4,000 bpd with flow pressures to 7,000 psig and temperatures to 350°F (177°C), while other fields may see less than 100 psig.

At the Christmas tree, the API 6A standard, Specification for Wellhead and Christmas Tree, generally prevails for manual and automated valve design and functionality. For ESD/PSD service, API 6A production or flow wing valves are usually reverse-acting gate valves designed for operating pressures typically ranging from 2,000 to 15,000 psig. The ESD/PSD valves on Christmas trees are normally and historically located on the production or flow arm of the tree upstream of the production choke. These wing valves and choke valves may or may not be automated, depending on ESD functionality.

 

When the valves are automated, some shale producers are now adding or moving the API 6A ESD valve and/or the ESD/PSD function to the downstream side of the choke to further protect downstream equipment. This is so that, should the choke or other equipment fail, such as when a choke suddenly washes out from unanticipated wear or “slugs,” alternating slugs of gas or liquid/solids downstream don’t severely damage equipment such as heat exchangers and production separators. Traditionally, at the Christmas tree, ESD/PSD-equipped API 6A valves are hydraulically powered or in some fields powered by compressed air. However, a newer development is that API 6A ball valves are gaining acceptance for some fields and applications.

 

There has been a substantial increase in the demand for stand-alone or manual hydraulic, self-contained shutdown systems, in part because of best practice decisions made in the field as well as the sheer volume of shale play wells with new, inexperienced or learning curve operations. It is also because of the remoteness of these shale plays (not just measured in miles, but also measured by available manpower to well count allocations or densities).

 

Stand-alones or manual afford ESD/PSD protection with little or no additional control or power supply infrastructure required. Self-contained, manually powered units also have at least one advantage over most traditional units in that they do not rely on external power sources. Instead, they are powered by hand-pumping a small manual hydraulic pump located at the actuator. This attribute makes them adaptable for locations where alternate power sources are not available or may be considered less dependable.

- See more at: http://www.valvemagazine.com/

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