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Uniset Flow Control System
Uniset Flow Control
Flexible Working Monobore Design
In many cases Weatherford aims to produce a Uniset working
monobore flow control completion design. The result is a well
design that allows through-tubing retrievable mechanical bridge
plugs to be run into the liner, yet still allows the use of landing
nipples in the upper completion. The Uniset working monobore is a
truly flexible design. It uses nipples for simple, reliable, low-cost
well completion and servicing and bridge plugs for redundant well
plugging later in field life.
Fundamental Nipple Sizing Rules
The fundamental nipple sizing required for completion optimization
can be described with the following generic rules:
— The tubing hanger profile should not give an ID restriction over the
tubing string run below it. For example, the tubing hanger profile should
have a minimum ID greater than tubing drift. The tubing hanger plug
should have a maximum OD less than the drift ID of the Christmas tree
valves.
— The insert safety valve profile should be selected so that the lock that
runs into it has an OD that results in the lock running at an OD equal to
the drift of the tubing above. If necessary, run above tubing drift but only
where special drifting of the tubing above tubing-retrievable, surface-
controlled subsurface safety valve (TRSCSSV) is possible. We
recommend that the QX lock mandrel itself (with keys removed) be
used as the drift.
— All flow control devices (plugs and landing nipples) should be sized to
give reasonable running clearances to enhance wireline installation
success. Typical acceptable running clearances are 0.030 in. (0.762
mm), depending on well trajectory and depth. Tighter running clearances
can be tolerated.
— Whenever possible the minimum restriction in the tubing should be
such that a mechanical bridge plug can be run, set and retrieved in the
liner section below.
— Whenever possible every major plugging point (landing nipple) should
have the contingent ability to install a mechanical retrievable bridge
plug above it. If necessary this should be accomplished with the use of
short sections of heavier-walled tubing.
— Where physical depth control is required without a sealing or plugging
requirement, an overdrift depth correlation sub (DCS) should be used in
preference to a landing nipple. DCSs can be combined with controlled-
ID pup joints for contingency bridge plug service.
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