Reducing
slip-crushdamage
totubulars
Deepwater drilling prospects aremoving toward
deeper water depths and deeper reservoirs below themud-line.
Wells, such as those drilled in the lower tertiary trend of the Gulf of Mexico
and in other areas of theworld, require operators to set large-diameter
casing strings at deeper depths. The depth of thewell not only requires
long casing strings, but it also requiresmore intermediate strings to be
set at deeper depths. To achieve this, mixed landing strings are needed,
which often incorporate the rig’s drill string. The drill string typically has a
reducedwall thickness and contains slipmarks, whichmake the potential
for slip crush evenmore critical. This has generated a need not only for
high-capacity drillpipe landing strings, but also high-capacity drillpipe
handling tools to land these heavy casing strings safely.
This slip-crush dilemma is a pivotal one for the industry for a number
of reasons. Themost likely slip-crush peril is localised drillpipe yield and
damage, necessitating associated inspection and repair costs. More critical,
though, are possibleworse scenarios, such as tubular crush and/or parting,
possibly even dropping the landing string. Such
incidentswould entail downtime, potential injuries, and
recovery – in short, substantial costs. With somuch at stake, the
company targeted this issue proactively, leading to the development of
advanced slip-crush capacities in its high-capacity drillpipe equipment.
Previous methodologies
Since 1959, the standard for calculating crushing loads on tubulars has
been the Spiri-Reinhold Equation. Recently, however, certain limitations
when using this particular formula have been indentified. Not only does
this formula fail to take into account intra-wall bending between slip
segments, but it does not addressmeridional bending or circumferential
bending stress (end effects).
Further complicatingmatters is the fact that one of the company’s
long-running research and testing programmes analysed and quantified
evenmore specific factors involved when crushing loads effect tubular
goods failure. Some of the identified causatives behind these increased
tubular stresses are handling equipment design, vessel heave-induced
dynamic loading, dynamic loading during tripping, and handling
equipment-related slip-crush loading. This revelation led to FI’s research
and development of a comprehensive analytical model that canmore
accurately predict the failure of tubulars due to slip crush.
Multifacetedtestapproach
To further develop its understanding of slip crush, the company utilises the
latest in finite element analysis (FEA). Computermodels are generated that
Robbie Thibodeaux, Jeremy Angelle,
and Logan Smith, Frank’s International,
USA, introduce a safe solution for
landing increasingly heavy strings.
O
ver the last 50 years, the oil and gas industry has continually
pushed the limits of exploration, riding thewave of recent
technological advances to pioneer ultra-deepwater areas of the
globe. Not until the early 80s though, did operators start delving below
the salt canopy. This sub-salt trend expandedwell programme depths in
excess of 35 000 ftMD, inwater depths exceeding 10 000 ft, necessitating
longer, heavier casing/landing strings.
Meanwhile, newgovernment regulations have begunmandatingwell
designs capable of sustainingworst case discharge (WCD). Deeper casing
strings, in turn, must nowbe constructed towithstand higher collapse
loads, shallowcasing strings to handlemore robust burst loads. Certain
well designsmust even feature an intermediate tieback able to endure
WCD, where previously a nested liner was sufficient.
This confluence of increasingly deepwells and stringent regulations
presents challenges. Longer, heavier casing/landing strings push the
limits of existing tubular tensile capacity, but as important, they also raise
concerns about handling equipment possibly crushing landing strings due
to excessive radial load (slip crush).
Frank’s International’s (FI) new line of high-capacity
drillpipe equipment not only enables operators to
land strings in excess of 2million lb, but
it does sowithout incident or
damaging tubulars.
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