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Typical DGWS Wellhead Configuration |
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This is a typical DGWS wellhead configuration. This configuration
prevents excessive tubing pressure build-up if a failure downhole
occurs. Failures that could occur is hole(s) develops in the
tubing, the downhole stuffing box (DSB) leaks, the insert
pump becomes unseated and or etc. However, if the DSB tool
leaks it could leak either way, up or down. If the DSB does
develop a leak, it is a very small (drip) leak. See DHI's
Manual of Practice (MOP) for more information.
The surface backpressure valve (12) must be set so that the
maximum pressure in the tubing at the surface cannot exceed
50psig. In addition, all of the valves except for the 2"
and 1" valves that have the bull plugs screwed in must
be fully open during operation. The bull plugs are present
to prevent a spill if the valves develop a leak. Therefore,
the bull plugs must always be securely tighten into the valves
when personnel is not present at the wellsite.
The inhibited/lubricated fluid in the tubing will evaporate
if the tubing is vented at the surface. In addition, this
fluid can expand after initial start up, resulting in increased
pressure at the surface. After initial start up gas and or
air that is entrained or dissolved in the inhibited/lubricated
fluid will build up at the surface and this gas must be vented
off and that volume replace with inhibited/lubricated fluid.
See DHI's installation procedure for more information.
The surface tubing pressure and fluid level in the tubing
must be monitored to insure proper DGWS operation. For more
information about DGWS monitoring and control see DHI's Manual
of Practice.
All valves, nipples, tees, elbows, plugs, connectors, plumbing
and pipes must be sized and the appropriate grade/rating to
withstand the operational pressures and flows. Insure that
all surface connections are properly lubricated, sealed and
fastened before operation.
Well Head
When selecting a well head the casing size, weight and
thread must be known. The inner string is tubing and most
of the time will be 2 3/8". The tubing string must be
suspended by slips or hangers. The tubing is set in tension
at the surface on all standard RFI systems. See DHI's installation
procedure for more information. The casing head pressure rating
(2000 to 3000psig) must be properly selected and the side
outlets are most often 2" LP size. The packing material
either nitrile or other seal/o-ring materials must be properly
selected.
For more information about wellheads see: http://www.rmenergy.com/pdf/hercwellhead.pdf |
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