Stuck p

pipe
p
Stuck pipe

1. Introduction :

When the drill string is no longer free to move up, down, or rotate
as the driller wants it to, the drill pipe is stuck.

Statistcs show that the drill string or casing will become stuck on
one of two wells drilled off shore.

Sticking can occur while drilling, making a connection, logging,

testing, or during any kind of operation which involves leaving the
equipment in the hole.

St k pipe
Stuck i can also
l result
lt in
i breaking
b ki a partt off the
th drill
d ill string
t i i the
in th
hole, thus losing tools in the hole.
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The consequences of a stuck pipe are:

 Lost drilling time when freeing the pipe.

 Time and cost of fishing: trying to pull out of the hole the broken
part of the BHA.

 Abandon the tool in the hole because it is very difficult or too

expensive to remove it.
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2. Cause of stuck pipe

2.1 Poor hole cleaning

If the cuttings are not removed

from the well properly, they will
settle around the drill string,
g, the
BHA, causing the drill collars to
become stuck.

The problem is worse in overgauge

hole sections where the annular
velocity is lower.
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In highly deviated wells, the cuttings tend to settle on the low side of
the hole and form cuttings beds.

Causes

 Drilling at excessive rates of penetration for a circulation given

((Faster cuttings
g ggenerated).
)
 Inadequate annular hydraulics.
 Inadequate mud rheology or not adequately sweeping the hole.
 Highly deviated wells path, beds of cuttings will form.
 Not circulating enough to clean the hole before tripping out or on
connections.
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Warning Signs

 Insufficient cuttings on shaker.

 Excessive overpull at connections and tripping.
 Fill on bottom
b tt after
ft connections
ti and
d tripping.
t i i
 Reduced overpull when pumping.
 Increase in torque,
torque drag and pump pressure.
pressure

Identification

 Stuck shortly after pumps are shut off.

 Circulation lost.
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Preventive action

 Circulate all cuttings out before tripping out.

 Maintain proper mud rheology in accordance with hole size, ROP
and
d hole
h l inclination.
i li ti
 Check shale shakers to see if the cuttings are being removed.
 In vertical wells,
wells sweep the hole with high viscosity mud and with
a low viscosity/High viscosity mud pills in highly deviated wells.
 If motor is used,
used rotate before tripping out of hole.
hole
 Use drillstring motion (Rotate & Reciprocate) while circulating at
the maximum rate to disturb cuttings beds.
beds
 Higher annulus velocities and a high viscosity at low shear rates in
highly deviated wells.
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2.2 Formation related problems

 Reactive or overpressured shales can result in a reduction in the

diameter of the borehole.
 Salt
S lt formation
f ti and
d some shales
h l plastics
l ti can flow
fl i t the
into th hole
h l .
 Fracturated formations can cause bridging and a packed of
annulus.
annulus
 Unconsolidated formations (Poorly cemented sands) cause
mechanical sticking of the string.
string
 Inter bedded formations create problems in deviated wells. The
soft formations tends to wash out,
out leaving ledges.
ledges
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a. Chemically Active Formations

A water sensitive shale is drilled

with less inhibition than is required.

Some high clay content rocks

absorb water and swell.

The amount of swelling varies from

highly reactive “gumbo” (fast
absorption rate) to shales, which
absorb water very slowly.
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As a result, amount of shale will break-off and fall into the borehole.

The water-absorbed (hydrated) shale tends to stick to the drill string

and accumulate in sufficient quantities to fill the entire annulus around
the BHA, causing it to become stuck.
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Warning Signs

 Large clumps of hydrated shale (Gumbo) coming out of the hole.

 Drilling rate is slower as less weight gets to the bit.
 BHA packed off .
 Increase in pump pressure.
 Increase in drag and torque as the hole size is reduced due to
swelling.
Increase in LGS, filter cake thickness, PV, YP, MBT.
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Identification

 Cannot circulate mud.

 Sticking can occur during any operation while in open hole.

Preventive Action

 Open hole time in shale should be minimised.

 Cased off rapidly

 Maintain mud inhibitors and encapsulating polymer at high levels.

 Minimize length of BHA and open hole sections.

 Regular wiper trips or reaming trips.

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b. Fractured and Faulted

Formation

A natural fracture system in the rock

can often be found near faults.
Rock near faults can be broken into
large or small pieces.
If they are loose they can fall into the
well bore and jam the string in the
hole.
There is a risk of sticking when
drilling through a fault and when
d illi
drilling th
through
h fractured
f t d limestone
li t
formations.
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Warning Signs

 Hole fill on connections.

 Possible losses or gains.

 Large quantities and blocky shales when drilling with underbalanced

 Fault damaged cavings at shakers.

 Increase in pump pressure, torque and drag.

Identification

 Sticking can be instantaneous.

 Circulation restricted or impossible.
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Preventative Action

 Minimise drill string vibration.

 Ream fractured zones cautiously.

Choose an alternative RPM or change the BHA configuration if

high shock vibrations are observed.

 Slow the trip speed before the BHA enters a suspected

fractured/faulted area.

 Circulate the hole clean before drilling ahead

 Anticipate
A ti i t reaming
i d i
during t i
trips.
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c. Overpressured Formations

A different type of instability occurs

when the formation pressure
exceeds the mud hydrostatic
pressure.

In this case the rock is able to

support the extra stresses when the
drill bit has passed.

An additional stress is applied to the

rock if the hydrostatic pressure is
less than the formation pore
pressure.
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The shale pieces can sufficiently accumulate to pack off the BHA
and cause sticking.

Warning Signs

 Large, brittle, concave shaped carvings.

 Cuttings / cavings show no sign of hydration.

 Absence of permeable formations.

formations

 Large overpulls at connections.

 Circulating restricted or impossible.

 Increased torque and drag.

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d. Tectonically Stressed
Formations

When a hole is drilled in an area of

hi h
high t t i
tectonic stresses
t th
the rock
k
around the well bore will collapse
into the well bore and produce
splintery cavings.
In the tectonic stress case the
hydrostatic pressure required to
stabilise the well bore may be much
higher than the fracture pressure of
the other exposed formations
This mechanism usually occurs:
In or near mountainous regions.
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Warning Signs

 Pack-offs and bridges may occur.

 Cavings at the shakers.
 IIncrease torque
t and
d drag.
d
 If stuck, circulation is likely to be impaired or non-existent.
 Increase in volume of returns at the shakers relative to the hole
volume drilled.

Preventative action

 Plan to case off these formations as quickly as possible.

possible
 If possible drill these formations in smaller hole sizes.
 Ensure that the circulation system is capable of handling the
additional volume of cavings
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2.6 Unconsolidated Formations

This mechanism is normally

associated with shallow formations.

 Loosely compacted sands and

gravel can sometime collapse
g p into
the wellbore forming a Bridge.

 It happens in a well bore when

little or no filter cake is present.
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Warning Signs

 Torque,
T drag
d and
d fill on connections
ti

 Overpull
p on connections.

 Unconsolidated, uncemented sand in sample (Shakers blinding).

 Increase in pump pressure.

Stuck Identification

 Circulation
Ci l ti restricted
t i t d or impossible.
i ibl

 Stuck shortly
y after p
pumps
p are turned off.
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Preventive Actions

 Identify sand or porous formations.

 Maintain a high gel mud and provide a good quality filter cake.

 Avoid excessive flow rate and unnecessary reaming or circulating

with BHA opposite this formations.

 Monitor pump pressure and drill cuttings.

cuttings

 Pick off bottom and circulate.

 Use sweeps to help keep the hole clean

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2.7 Mobile Formations

The overburden on weight and

tectonic forces from the rock above
will
ill tend
t d to
t squeeze the
th salt
lt or shale
h l
out into the wellbore.

Mobile formations behave in a

plastic manner, deforming under
pressure.

The deformation results in a

decrease in the well bore size,
causing
i problems
bl running
i BHA’
BHA’s,
logging tools and casing.
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Warning Signs

 Increase in mud chlorides.

 Large overpulls and torque at connections.

 Pump pressure increase.

Stuck Identification

 Stuck shortly after pumps are turned off.

 Rotation may be possible but with high torque.

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Preventive Actions

 Plan frequent reaming/wiper trips

 Consider using a slightly under

under- saturated mud system

 Maintain sufficient mud weight.

 Identify salt dome.

 Monitor mud chlorides and mud resistivity.

 Trip in slowly and ream.

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2.8 Undergauge Hole

Drilling hard abrasive rock wears the

bit and the stabiliser gauge and
results
lt in
i a smaller
ll ththan gauge hole.
h l
This mechanism occurs:
 After running a new bit.
bit
 After coring.
 When a PDC bit is run after a roller
cone bit.
 When drilling abrasive formations.
formations
Warning Signs
 Undergauged bit and stabilizers.
 Sudden setdown weight.
 Low ROP.
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Stuck Identification

 Stuck while tripping into hole.

 Circulation is unrestricted or slightly restricted.

Preventive Actions

 Identify abrasive, hard formations.

 Use suitably gauge-protected bits and stabilisers.
stabilisers
 Trip in slowly.
 Consider the use of roller reamers.
reamers
 Ream suspected undergauge sections.
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2.9 Key Seating

A key seat is caused by the drill

string rubbing against the
formation.

The body and tool joints of drill

pipe wear a groove in the rock
about the same diameter as the
tool joints.

During a trip out of the hole, the

BHA may be pulled into one of
these grooves, which may be too
small for it to pass though.
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This mechanism occurs:

 Where
Wh high
hi h side
id wall
ll forces
f and
d string
t i rotation
t ti exist.
i t

 While p
pulling
g out of the hole.

 The number and severity of dog-legs.

 The drillability of the formation.

 The relative size between the drill pipe tool joints and the drill
collars.
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Warning Signs

 Large doglegs.
 Erratic overpull.

Stuck Identification

 Stuck while tripping out.

 Circulation unaffected.

Preventive Actions

 Consider running string reamers or a key seat wiper.

 Drill with a stiff bottomhole assembly, which tends to minimize
the chance of severe dog Legs.
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2.10 Wellbore Geometry

These are formed when successive

hard / soft interbedded formations.

Ledge: The well bore passes

through
g rock of varying
y g types
yp and
ledges develop at the interfaces
between layers of differing
hardness.

Doglegs: While drilling a well

bore, the characteristics of the rock
cause the
th bit to
t be
b deflected
d fl t d and
d
can result in a change in direction.
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Warning Signs

 Sudden erratic overpull or setdown.

 Problems are at fixed depths.
 Prognosed
P d hard
h d soft
ft interbedded
i t b dd d formations.
f ti

Stuck Identification

 Full circulation is possible.

 Stuck after a change in BHA.

 While tripping, the stabilizer blades may become stuck under the
ledges .
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Preventive Actions

 Minimise direction changes in the well bore.

 Minimise BHA configuration changes when in formations likely to

produce ledges.

 Consider reaming trips.

 Increasing
I i th well
the ll bore
b survey frequency
f will.
ill

 Make a log
g of depths
p of ledges
g and other anomalies.

 Slow trip speeds before BHA enters the suspected ledge zone or
dog leg.
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 Slow trip speeds before BHA enters the suspected ledge zone or
dog leg.

 Avoid prolonged circulation across soft interbedded formations.

 Do not start angle building operations too close to the shoe (At
least 30m below old hole TD).
)
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2.11 Junk

Metal junk that has fallen into the

hole from the rig floor or from
downhole equipment, which falls
down the well bore and jams the
drill string.

This mechanism usually occurs:

 Due to poor housekeeping on the

rig floor.
 Due to the hole cover not being
installed.
 Downhole equipment failure.
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Warning Signs

 Repair/maintenance work recently performed on the rig floor.

 Missing hand tools / equipment.

 Metal shavings at shaker.

 Sudden erratic torque.

 Inability to make hole.

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Stuck Identification

 Circulation unrestricted.

 Stuck shortly after downhole equipment failure.

Preventive Actions

 Encourage good housekeeping.

 Keep the hole covered at all times.

 Inspect downhole equipment before it is run in the hole.

 Inspect slip and tong dies regularly.

 Install drill string wiper rubber as quickly as possible.

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2.12 Collapsed Casing

External pressures exceed the casing

strength.
The casing is not cemented properly.

Casing wear due to friction or

corrosion decreases the effective
collapse pressure rating of the
casing, through decreased wall
thickness.
thickness

Collapse is often discovered when

the BHA is run into the hole and
hangs up inside the casing.
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Warning Signs

 BHA hangs up when RIH.

 Caliper log shows collapsed casing.

Stuck Identification

Stuck while tripping through casing.

Preventive Actions

 Avoid casing wear, refer to casing wear guidelines.

 Good cementing practices should be used.
 Use corrosion inhibitors in fluids.
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Cement Related
2.13 Cement Blocks

These problems can only occur

d i
during, or shortly
h tl after,
ft a cementt job.
j b
Blocks of cement around the casing
shoe may fall into the hole.
hole

Warning Signs
Large cement fragments at shakers.
Stuck Identification
 Circulation unrestricted.
 Rotation and downward movement
may be possible.
 Erratic torque.
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Preventive Actions

 Ream casing shoe and open hole plugs thoroughly before drilling
ahead.

 Limit casing rat hole length to minimise a source of cement

blocks.

 Slow the trip speed down before the BHA enters the casing shoe or
the plug depth.

 Use of fibre additives to the cement can increase its integrity.

integrity
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2.14 Green Cement

The top of the cement may be higher

than prognoses.

When the drill string is inadvertently

run into cement,, the cement can flash
set.

If the drilling assembly is run at too

high a speed, it is possible to become
stuck in “green” cement.

Flash setting
“Flash setting” of cement can also
result in the pipe becoming stuck.
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Warning Signs

 Increase in pump pressure leading to inability to circulate.

 Loss of string weight.

 Sudden decrease in torque.

 Green cement in mud returns.

Stuck Identification

Stuck while running into the hole to dress off cement.

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Preventive Actions

 Do not rely solely on surface samples.

 Know the cement setting time, but do not assume it will be set
when you trip in to the hole.

 Know the calculated top of cement before tripping in hole.

 Do not rely on the weight indicator to find the top of the cement.
cement

 Control drilling when cleaning out soft cement.

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2.16 Differential Sticking

Differential sticking is defined as stuck pipe caused by the differential

pressure forces from an overbalanced mud column acting on the
d ill t i
drillstring against
i t a filter
filt cake
k deposited
d it d on a permeable
bl formation.
f ti

Two conditions must exist:

 When a permeable formation is drilled, mud filtrate will enter the

rock and deposit a filter cake of solids on the sides of the hole.

 If the difference in pressure between the column of mud and the

formation pressure is high, the risk of becoming stuck is also high.
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This mechanism occurs:

 With a stationary or very slow moving string.

 Excessive embedded pipe length.
In a thick filter cake.
 High formation permeability.
 High positive differential pressure.

Warning Signs

 Overpull on connections and after surveys

l
Circulation is not restricted.
d
 High overbalance
 Permeable
P bl fformation
ti exposed
d in
i open hole
h l
 The string became stuck while stationary.
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Stuck Identification

 The pipe was stationary before it got stuck.

 Full circulation is possible.
 BHA adjacent
dj to thick
hi k sand.
d
 Hydrostatic pressure overbalance.

Preventive actions

 Where possible design casing setting depths.

 Reduce mud weight to the minimum required for hole stability.
 Use OBM where possible.
 Keep hole as straight as possible.
 Keep
K solids
lid content off mud
d as low
l as possible.
ibl
 Use extreme pressure (EP) lubricants.
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 Keep fluid loss to a minimum to reduce thickness of the filter cake.

 Minimize BHA length when possible by using Heavy weight drill

pipe.

 Use stabilizers and reduce the area of contact by using a spiral drill
collars.

Keep the pipe moving and run drilling jars when possible.

 Control ROP to limit the concentration of drill solids, this affect the
filter cake.
cake
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Remedial Measures

 Apply torque and tension to try to work the pipe free.

 Determine the stuck point, spot a diesel

diesel-oil
oil pill or other surfactant

 Spot soak solution in sufficient volume to cover BHA with 24 bbls

inside the drill pipe.

If backoff from the stuck portion has already been effected,
effected a
packer may be set above the fish to lower the differential pressure
around the stuck portion,
portion thereby freeing the pipe.
pipe

 Setting a cement plug and sidetracking may be necessary as a last

resort.
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Stationary pipe

If the drill pipe is not moved for a

period of time the filter cake tends
to build up around it and then add
to the differential sticking force that
is holding the drill collars.

The mud cake forms a bridge

between the drill collar and the
mud cake in the hole.
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Filter Cake Erosion

Filter cake erosion happens when the drill pipe rubs against the
borehole wall.
Thi only
This l affects
ff t a small
ll portion
ti off the
th circumference
i f off the
th wellbore.
llb
Wiper trip erosion happens when the stabilizers and the bit are pulled
through the mud cake and a significant amount of it is scraped off.
off
Most of the mud cake is removed when the hole is reamed.
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 Mixing Procedure

The actual volume required should be sufficient to fill the annulus

around the drill collars.

If practical, allow an excess of up to 50%.

 Add required volume of oil, ester or ether to the pit.

 Add the Avatensio /LT through a hopper.

hopper

 Add the water (drill water, sea water, or brine can be used)

 Add barite to required density.

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 Spoting Procedure

These consist of a blend of surfactants and emulsifiers mixed in

either a base oil or environmentally friendly fluid.
The spotting fluids reduces the surface tension between the well bore
and the drill string, it also penetrates the wall cake promoting it’s
removal from the wall bore
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The success of spotting fluid depends on

The volume displaced, the stuck point is located and sufficient pill is
mixed up to cover all the pipe below this point.

A 50% excess is normally mixed to cover for hole enlargement.

enlargement

Proper placement.

The pill is spotted across the stuck point leaving 10 bbls in the drill
string.
½ a bbl is then pumped every half hour while working the pipe.

The pill should be left for a minimum of 8 hours to soak before giving
up.
p If p
pipe
p is not free after 40 hours consider side tracking.
g

The pill should be pumped as soon as possible after getting stuck.

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Planing

 Data from offset wells will have studied to identify potential stuck
Pipe zones.

 This formation should be incorporated into a separate section of

the drilling
gpprogram.
g

 The casing design should, where possible, take account of these

zones.

 The selection of the type of drilling fluid and its operating

parameters will greatly influence the hole conditions.
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Drilling Practices

Some precautions that can be taken at the rig site.

 The driller must be aware of what to do if the hole becomes tight.

His reaction will be decisive in the prevention of a minor drilling

problem degenerating into a fishing operation.

Pulling up into a tight hole will frequently lead to stuck pipe.

pipe

Working the string down and circulating, is almost invariably the best
initial reaction.

 The
Th mud
d engineer
i should
h ld communicate
i t any problems
bl off poor hole
h l
cleaning or any difficulty maintaining good mud properties.
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Planing

 Data from offset wells will have studied to identify potential stuck
Pipe zones.

 This formation should be incorporated into a separate section of

the drilling
gpprogram.
g

 The casing design should, where possible, take account of these

zones.

 The selection of the type of drilling fluid and its operating

parameters will greatly influence the hole conditions.
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 The geologist and mud logger will keep the driller updated on
changes in formation and pore pressure.

 Many pipe sticking problems occur during a trip. The hole must
be circulated clean before tripping.
tripping

 On a high angel hole it will be necessary to circulate much longer

than just bottoms-up, to ensure the hole is clean by
Pumping a tandem of low/high viscous pills.

 The operator will provide guidelines on pipe running speed and

washing and reaming after a trip.
trip

 The last three joints are usually washed to bottom.

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 Wiper trips should be made regularly to identify any developing

problem higher up the hole.

The frequency of wiper trips is set by the operator, but it should

t k accountt off hole
take h l conditions.
diti

 The drill string

g must be kept
p moving
g while in open
p hole.

 The length and design of the bottom hole assembly will usually
be decided on the basis of the penetration, hole angle and
direction.

A long assembly with a large number of drill collars will

significantly increase the risk of becoming differentially stuck.
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