CHAPTER

15 Stuck Pipe

Introduction

Stuck pipe Stuck pipe is one of the more common Mechanical sticking is caused by a
is one of and serious drilling problems. It can physical obstruction or restriction.
range in severity from minor incon- Differential sticking is caused by differ-
the more venience, which can increase costs ential pressure forces from an overbal-
common slightly, to major complications, which anced mud column acting on the
and serious can have significantly negative results, drillstring against a filter cake deposited
such as loss of the drillstring or com- on a permeable formation. Mechanical
drilling plete loss of the well. A large percent- sticking usually occurs when the drill-
problems. age of stuck pipe instances eventually string is moving. It also is indicated by
result in having to sidetrack around obstructed circulation. Occasionally,
the stuck pipe called a fish and redrill however, a limited amount of up/down
the interval. Stuck pipe prevention mobility or rotary freedom is evident,
and remedy are dependent on the even when the pipe is mechanically
cause of the problem. Therefore, to stuck. Differential sticking usually occurs
avoid stuck pipe and correct it effi- while the pipe is stationary, such as
ciently, it is important to understand when connections are being made or
the various causes and symptoms so when a survey is being taken. It is
that proper preventive measures and indicated by full circulation and no
treatments can be taken. up/down mobility or rotary freedom
If the pipe becomes stuck, every effort other than pipe stretch and torque.
The probabil- should be made to free it quickly. The Mechanically stuck pipe can be
ity of freeing probability of freeing stuck pipe success- grouped into two major categories:
fully diminishes rapidly with time. 1. Hole packoff and bridges.
stuck pipe Early identification of the most likely 2. Wellbore geometry interferences.
successfully cause of a sticking problem is crucial, Packoffs and bridges are caused by:
diminishes since each cause must be remedied with Settled cuttings
different measures. An improper reac- Shale instability
rapidly with tion to a sticking problem could easily Unconsolidated formations
time. make it worse. An evaluation of the Cement or junk in the hole
events leading up to the stuck pipe Wellbore geometry interferences are
occurrence frequently indicates the caused by:
most probable cause and can lead to Key seats
the proper corrective measures. Undergauge hole
Stiff drilling assembly
Mobile formations
Please refer to the Worksheet:
Ledges and doglegs
Freeing Stuck Pipe and the tables
Casing failures
of stuck pipe causes, indications
Differentially stuck pipe usually
and preventative measures
occurs because of one of the following
all at the end of this chapter.
causes/high-risk conditions:
Refer to them as you review
High overbalance pressures
the material.
Thick filter cakes
High-solids muds
In general, pipe becomes stuck High-density muds
either mechanically or differentially.

Stuck Pipe 15.1 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

Mechanical Sticking

HOLE PACKOFF AND BRIDGES The causes of inadequate cleaning

If cuttings are Settled cuttings. If cuttings are not of cuttings from the hole are:
removed from the borehole, they accu- Drilling at excessive Rates Of
not removed Penetration (ROP) for a given
mulate in the well, eventually causing
from the the hole to pack off, often around the circulation rate. This generates
borehole, they Bottom-Hole Assembly (BHA) and stick- cuttings faster than they can be
ing the drillstring (see Figure 1). This circulated mechanically from
accumulate the annulus.
problem is encountered often in over-
in the well gauge sections, where annular velocities Inadequate annular hydraulics.
are reduced. In deviated wells, cuttings Failure to suspend and carry cuttings
will build up on the low side of the to the surface with adequate mud
hole and may eventually slump down rheology.
the hole, causing packoff. Highly deviated well paths. High-
angle wells are more difficult to
clean, since the drilled solids tend to
fall to the low side of the hole. Beds
of cuttings will form, which are not
easily removed.
Formation sloughing and packing
off around the drillstring.
Not circulating enough to clean the
hole before tripping out or making
connections. When circulation is
String interrupted, cuttings may settle
Cuttings bed Rotation around the BHA and pack off,
form while
drilling Circu
sticking the pipe.
latio
n
Drilling blind (without mud returns)
and not adequately sweeping the
_______________________ hole periodically with a viscous mud.
_______________________ Unintentionally drilling without
circulation.
_______________________
Ove

The major warning signs and

rpu
ll

_______________________
indications of cuttings settling are:
_______________________ Fill on bottom after connections
_______________________ and tripping.
Stuck
Few cuttings returning at the shakers
_______________________
Cuttings relative to the drill rate and hole size.
bed
_______________________ Increase in torque, drag and pump
_______________________ Packoff pressure.
Overpull on connections and while
_______________________
tripping out.
_______________________ Increase in Low-Gravity Solids (LGS)
Figure 1: Settled cuttings (after Amoco TRUE T). and possible mud weight and/or
_______________________
viscosity increases.
_______________________

_______________________

_______________________

Stuck Pipe 15.2 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

The main Preventive measures to minimize the The main indication that reactive
indication possibility of settled cuttings are: shale has been drilled are increases in
Maintain proper mud rheology in the funnel viscosity, yield point, gel
that reactive accordance with hole size, ROP and strengths, Methylene Blue Test (MBT)
shale has hole inclination. and, possibly, the mud weight. This
been drilled In near-vertical wells, sweep the will be reflected by increases in torque,
hole with high-viscosity mud. In drag and pump pressure.
are increases highly deviated wells, sweep with Pressured shales. These shales are
in the funnel low-viscosity/high-viscosity pills. pressured and mechanically stressed
viscosity, Always circulate until the sweeps by several different factors, includ-
have returned to the surface and the ing the weight of overburden, in-situ
yield point, shakers are clean. stresses, angle of bedding planes and
gel strengths Use optimized hydraulics compati- tectonic stresses. When drilled with
ble with the respective hole size, insufficient mud weight, these shales
inclination and ROP. Higher circula- will slough into the wellbore (see
tion rates always provide improved Figure 3).
hole cleaning.
Control drilling in high ROP or
marginal hole-cleaning situations.

Lower pressure
Use aggressive drillstring rotation for Higher
improved hole cleaning. pressure

Make a wiper trip after all long

motor runs.
Use drillstring motion (rotate and
reciprocate), while circulating at the
maximum rate to disturb cuttings
beds and reincorporate them into
the flow stream. Figure 3: Pressured formations.
Shale instability. Unstable shales can
cause packing off and sticking when Fractured and faulted formations.
_______________________ they fall into the wellbore. They may These are fragile formations which
be classified as follows: are mechanically incompetent. They
_______________________
Reactive shales. These are water- are particularly unstable when the
_______________________ sensitive shales drilled with insuffi- bedding planes dip at high angles
_______________________ cient inhibition. Shales absorb water, (see Figure 4).
_______________________
become stressed and spall into the
wellbore (see Figure 2). Mechanically
incompetent rock
_______________________

_______________________ Clay balls

_______________________

_______________________

_______________________
Softened
_______________________ Stabilizer reactive
balling and shale Fractures
_______________________ tight hole fault zone

_______________________

_______________________ Figure 4: Fractured and faulted formations

(after Shell UK).
_______________________ Figure 2: Reactive formation (after Shell UK).

Stuck Pipe 15.3 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

Large quantities of splintery or are common indicators of such prob-

blocky shale will be encountered when lems. Solids-control equipment will be
pressured shales are drilled underbal- overloaded with quantities of solids
anced or when fractured formations that do not correspond to the ROP.
slough. Pump pressure, torque and drag
will increase when the hole becomes
overloaded with caving shale.
Control of Control of formation instability
formation should start during the planning phase
of the well. An inhibited mud system,

Overpull
instability matched to the formation with the
should start proper mud weight, will minimize shale
during the instability. To balance mechanical
stresses, highly deviated wells require
planning higher mud weights than vertical wells.
phase Although the first priority of a casing
design is to ensure that the well can be
drilled safely, casing points may have
to be adjusted so that troublesome
formations can be cased off.
suitable Needless to say, suitable mud proper-
mud proper- ties must be maintained to ensure good Flowing
hole cleaning. If formation caving is sand
ties must be detected, respond immediately:
maintained 1. Stop drilling. Stuck

to ensure 2. Sweep the hole with viscous mud.

3. Increase the viscosity to improve Packoff
good hole the carrying capacity.
cleaning. 4. Increase the mud weight, when
applicable.
5. Implement drilling practices to Figure 5: Unconsolidated formation (after Amoco TRUE).
improve cuttings transport and to To drill these formations, the mud
reduce the possibility of pipe sticking. should provide a good-quality filter
Unconsolidated formations. This prob- cake to help consolidate the forma-
lem involves formations that cannot be tion so that hydrostatic pressure can
supported by hydrostatic overbalance push against and stabilize the for-
alone. For example, unconsolidated mation. Treatments with seepage-loss
sand and pea gravel often fall into the material, such as M-I-X-IIE fiber, will
hole and pack off around the drillstring. help seal these formations and pro-
Problems also occur if insufficient filter vide a base for the filter cake. To mini-
cake is deposited on loose, unconsoli- mize erosion, avoid excessive flow
dated sand to prevent it from flowing rates and avoid any unnecessary ream-
into the wellbore and packing off the ing or circulating with the BHA oppo-
string (see Figure 5). site unconsolidated formations. The
Generally, these types of formations hole should be swept with viscous gel
are encountered at shallow depths or sweeps to ensure good hole-cleaning,
when drilling the production zones. and filter-cake building.
Torque, drag and fill on connections

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 CHAPTER

15 Stuck Pipe

When cement Cement or junk in the hole. When Metal junk can fall from the rig floor
blocks or junk cement blocks or junk falls into the or come from failed downhole equip-
wellbore, they can act as a wedge and ment or pieces of milled tubulars and
falls into the jam the drillstring. This can happen equipment (see Figure 8).
wellbore, they when cement becomes unstable around
can act as a the casing shoe or from open-hole plugs
and kickoff plugs (see Figure 6).
wedge and
jam the
drillstring.
Dropped
Blocks Rathole objects
break loose below shoe

Figure 8: Junk (after Shell UK).

Some preventive measures to

Figure 6: Cement blocks (after Shell UK).
minimize junk in the hole are:
Limit the casing rathole to minimize
Another type of cement packoff can the source of cement blocks.
occur when circulation is attempted Allow sufficient cement setting time
with the BHA imbedded in soft before drilling out.
cement. Pump pressure can cause Maintain sufficient distance between
the cement to flash set and stick offset wells.
the string (see Figure 7). Begin washing down at least two
stands before the theoretical top of
the cement.
Pull up two stands before attempting
to circulate, if set-down weight is
_______________________ observed when tripping in the hole
BHA imbedded after a cement operation.
_______________________ in soft cement
Cement Control drilling when cleaning out
_______________________ soft cement.
_______________________ Keep the hole covered when the
_______________________
drillstring is out of the hole.
Maintain rig floor equipment in
_______________________
good operating condition.
Figure 7: Soft cement (after Shell UK).
_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Stuck Pipe 15.5 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

WELLBORE GEOMETRY Key seat sticking occurs when the pipe

A second category of mechanically becomes wedged into the narrow slot of
stuck pipe is related to wellbore geome- the key seat as it is pulled up. Key seat
try. Hole diameter and/or angle relative sticking occurs only when the pipe is
to the BHA geometry and stiffness will moving. The pipe also may become dif-
the higher not allow passage of the drillstring. ferentially stuck after being key seat
the change Generally, the higher the change in stuck. Pipe stuck in a key seat often can
well angle or direction, the higher the be freed by jarring downward, especially
in well angle if sticking occurred while picking up.
risk of mechanically sticking the pipe.
or direction, S-shaped wells are even worse and Undergauge hole. Abrasive hole sec-
the higher put an additional risk of pipe sticking tions not only will dull bits, but also
the risk of due to increases in friction and drag. will reduce the gauge of the bit and
The main types of well geometry stabilizers. Pushing a bit run too far
mechanically interference are: in abrasive formations leads to under-
sticking Key seating. Key seats occur when the gauge holes. Running a full-gauge
the pipe. drillstring rubs against the formation assembly into an undergauge hole
on the inside of a dogleg. The drill- can jam and stick the string (see
string is held against the wellbore by Figure 10).
tension as pipe rotation and move-
ment wear a narrow groove in the side
of the hole. The longer the interval
below the dogleg and the more severe
the dogleg, the greater the side load Previous undergauge
bit and BHA
and the faster the development of a
key seat (see Figure 9).
Abrasive
formation
Tens
n io
Ro

ati
t

on

Side
load
_______________________

Set down weight

W

_______________________
eig
ht

_______________________
New full-gauge
_______________________ Slot worn into bit and BHA
formation
_______________________

_______________________
Stuck
_______________________

_______________________

_______________________ Figure 10: Undergauge hole (after Amoco TRUE).

Overpull

Stuck while
_______________________ POOH
Stiff assembly. Holes drilled with lim-
_______________________
ber BHAs may appear to be straight
_______________________ when tripping out, but if a stiffer BHA
_______________________
BHA is run, the newly drilled hole will act
as if it were undergauge. Flexible
_______________________
Figure 9: Key seat (after Amoco TRUE).
_______________________

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 CHAPTER

15 Stuck Pipe

assemblies can snake around doglegs region, but generally is greater for for-
that present obstructions to stiff assem- mations below 6,500 ft (2,000 m) and
Stiff BHAs blies. Stiff BHAs cannot negotiate sharp for salt formations with temperatures
cannot hole angle/direction changes and can above 250F (121C) (see Figure 12).
become jammed (see Figure 11). Ledges and micro-doglegs. These
negotiate are formed when successive hard/soft
sharp hole interbedded formations are encoun-
angle/ tered. The soft formations become
POOH with
direction limber BHA washed out for various reasons (i.e.
excessive hydraulics, lack of inhibition),
changes while the hard rocks remain in gauge.
This situation is aggravated by dipping
formations and frequent changes in
angle and direction. The stabilizer
blades may become stuck under the
ledges during tripping or picking up
for connections (see Figure 13).

RIH with
Stuck stiff BHA

Se
td Hard
ow
n

Stuck
Soft or
unstable

Hard

Stabilizers
hang up on
ledges
Figure 11: Stiff assembly (after Amoco TRUE).

Mobile formation. The overburden Figure 13: Ledges (after Shell UK).

Casing- weight or tectonic forces can squeeze Casing failures. Casing-related fail-
plastic salt or soft shale into the well- ures can stick the drillstring. The cas-
related bore, sticking or jamming the BHA in ing will collapse if external pressures
failures can the undergauge hole. The magnitude exceed the casing strength. This situa-
stick the of the stresses and hence the rate of tion happens often opposite plastic
movement will vary from region to formations. Salt formations become
drillstring.
increasingly plastic with pressure and
Overburden pressure
temperature, and are often associated
with collapsed casing.
If the casing is not cemented prop-
erly, the bottom joint or joints can be
Plastic
deformation
unscrewed by drillstring rotation. If this
occurs, the casing below the unscrewed
connection may drop and turn at an
angle in the hole, catching the drill-
Hole closes after
drilling through string (refer to Figure 8). Proper casing
running practices (tack welding or
chemically bonding the first few collars)
Figure 12: Mobile formation (after Shell UK).

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 CHAPTER

15 Stuck Pipe

and a good cement job will minimize Drill salt sections with eccentric,
the likelihood of this problem. bi-centered Polycrystalline Diamond
The following practices are recom- Compact (PDC) bits. Plan regular
mended to minimize wellbore geometry wiper trips to ream open-hole sections.
sticking: Use higher-strength casing opposite
If a key seat is expected, use a key plastic formations.
seat reamer. Run a liner inside casing through
If abrasive formations are drilled, the entire salt interval for additional
use hardfaced stabilizers and bits strength.
with extra gauge protection. Drill salt with oil-base or synthetic
Gauge the old bit and stabilizers as muds to maintain a gauge hole
well as the new ones on every trip. through the salt and provide a better
Ream the last stand or three joints cement job with more even distribu-
back to bottom on every trip. tion of stresses on the casing through
Optimize BHA design and stiffness. the salt.
Plan a reaming trip if a stiff BHA is run Slow down the running speed before
and/or if a hole geometry problem is the BHA enters a kickoff or dogleg.
suspected. Minimize dogleg severity and/or sharp
If mobile salt is encountered, use and frequent wellbore course changes.
an undersaturated mud system to Avoid prolonged circulation oppo-
wash the zone or use a higher site soft formations to prevent hole
mud weight to stabilize it. washout and formation of ledges.

Differentially Stuck Pipe

Differential sticking is defined as stuck the hydrostatic pressure of the mud is
pipe caused by the differential pressure 500 psi greater than formation pressure.
forces from an overbalanced mud col- In A, the drill collars are centered in
umn acting on the drillstring against a the hole and are not stuck. The hydro-
filter cake deposited on a permeable for- static pressure acts equally in all direc-
Many mation. Many occurrences of stuck pipe tions. In B and C, the collars contact
occurrences can be attributed to differential pressure the filter cake opposite a permeable
sticking, which also is referred to as zone, and become stuck. As shown in
of stuck wall sticking. It usually occurs while C, the hydrostatic pressure now acts
pipe can be the pipe is stationary during a connec- across the area of contact between the
attributed to tion or when taking a survey, and is filter cake and the collars. This pressure
indicated by full circulation and no holds the collars firmly against the wall
differential up/down mobility or rotary freedom, of the hole. The segment this force acts
pressure other than pipe stretch and torque. upon is shown by the dotted line
sticking For differential sticking to occur, two drawn across the drill collar from a
conditions must exist: to b. The distance from a to b
1) The hydrostatic pressure of the depends on the imbedded depth of
mud must exceed the pressure of the collar/pipe into the filter cake, and
the adjacent formation. the hole size and the OD of the pipe.
2) A porous, permeable formation The imbedded depth depends on the
must exist. thickness of the filter cake, which deter-
Figure 14 demonstrates the mechanics mines the area of contact between the
of differential sticking. In this example, pipe and the wall cake. The thickness of

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 CHAPTER

15 Stuck Pipe

_______________________ A B C

_______________________
758-in. hole
6-in. drill collars
_______________________ 20-ft section of collars

Filter cake
_______________________ Stuck
Mud hydrostatic pressure
_______________________ 5,000 psi

_______________________
Filter cake
_______________________
a

Drill collars

Drill collars
_______________________ Drill Formation
collar pressure
_______________________ b 4,500 psi

Mud

Mud

Mud
_______________________

_______________________ a b = 3.75 in.

_______________________

_______________________ Figure 14: Mechanics of differential pressure sticking.

_______________________ the filter cake is a function of the con- pipe is stuck. This combination of
_______________________ centration of solids in the mud and the differential pressure and a permeable
fluid loss. In this example, for every formation results in fluid loss to the
square inch of contact area, there is a formation and the deposition of a
confining force of 500 lb. For a 20-ft filter cake.
section of 6-in. collars in a 758-in. hole Almost always, there is free circula-
imbedded 18-in. into the filter cake tion around the stuck zone when pipe
(a b is 3.75 in.), the calculated is differentially stuck (i.e. no packoff).
differential strength force is: When a filter cake builds up on the
(500 psi) (3.75 in.) (20 ft) (12 in./ft) formation, it increases the contact
= 450,000 lb area between the wellbore and the
drill pipe. Excessive drill solids and
To calculate the vertical force neces- high fluid loss increase filter-cake
Excessive sary to pull the pipe free, this force is thickness and the coefficient of fric-
multiplied by the coefficient of friction. tion, making it more difficult to pull
drill solids The coefficient of friction is usually in or jar the drill pipe free.
and high the range of 0.2 to 0.35 in water-base
fluid loss muds and 0.1 to 0.2 in oil-base or syn- PREVENTIVE MEASURES
thetic muds. In this case, the vertical All of the conditions associated with
increase force necessary to pull the pipe free differentially stuck pipe cannot be
filter-cake is 45,000 lb with a 0.1 coefficient of eliminated; however, the possibility
thickness friction and 135,000 lb with a 0.3 of differential sticking can be reduced
coefficient of friction. by following good drilling practices.
These include the following:
CAUSES
Reduce the overbalance pressure by
When the pipe becomes differentially keeping the mud weight as low as
stuck, the following conditions exist: good drilling practices allow. Excessive
The hydrostatic pressure of the mud weights increase the differential
mud exceeds the adjacent pressure across the filter cake and
formation pressure. increase the possibility of differentially
The formation is permeable (usually sticking the pipe.
sandstone) at the point where the

Stuck Pipe 15.9 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

Reduce the area of contact between annulus. This affects differential

the wellbore and the pipe by using pressure and filter-cake composition.
the minimum length of drill collars Minimize the muds coefficient of
needed for the required bit weight. friction by keeping a good quality
Reduce the area of contact by using filter cake with low drill solids and
small, spiral or square drill collars; by by using the proper lubricants in
using stabilizers; and by using heavy- sufficient quantities.
weight drill pipe to supplement the Keep the pipe moving when possible
weight of the drill collars. and use good drilling practices to
Reduce filter-cake thickness. Thick minimize differential sticking.
filter cakes increase the contact area Run drilling jars when possible.
between the pipe and the side of Watch for depleted pressure zones,
the hole, which effectively reduces where differential sticking occurs
wellbore diameter. The contact area frequently. The mud weight used to
between the wellbore and pipe can be drill these zones must be sufficient
decreased by reducing the thickness of to balance the normal pressure gra-
Filter-cake the filter cake. Filter-cake thickness can dient of the open hole. The differ-
thickness be reduced by lowering the filtration ence in pressure of the normally or
rate and drill solids content. abnormally pressured zones exposed
can be Maintain a low filtration rate. in the wellbore and the pressure of the
reduced by Filtration rates should be monitored depleted zone can be several thousand
lowering the on a regular basis at downhole tem- pounds per square inch. Seepage-loss
peratures and differential pressures. materials such as asphalt, gilsonite,
filtration Mud treatment should be based on M-I-X II fiber and bridging agents
rate and the results of these tests relative to such as sized-calcium carbonate have
drill solids desired properties. been used with success to drill depleted
Control excessive ROP to limit the zones with high differential pressures.
content. concentration of drill solids and Depleted zones should be isolated with
an increase of mud weight in the casing whenever possible.

Common Stuck Pipe Scenarios

Stuck pipe can often be freed. However, 2. Pipe sticks while tripping into the
it is it is critical first to determine why the hole (pipe moving) with the bit and
criticalto pipe is stuck. BHA below the casing shoe. It is
Some of the most common stuck pipe impossible to rotate the pipe.
determine situations, with the most common If stuck off bottom, and the
why the pipe ways to free it, are as follows: BHA has been lengthened or
is stuck. 1. Pipe sticks while tripping into stiffened, the string probably
the hole before the bit reaches has been wedged into a dogleg.
the casing shoe. Circulation should be possible,
If it is possible to circulate, the but may be restricted.
casing probably has collapsed. If the pipe is stuck close to
If it is not possible to circulate, and bottom, it may be jammed into
the mud is cement-contaminated an undergauge hole or dogleg.
or contains a high lime concentra- Circulation should be possible,
tion, the pipe is probably stuck in but may be restricted.
cement or contaminated mud.

Stuck Pipe 15.10 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

If it is not possible to circulate, pipe 4. The pipe sticks when circulating

is stuck in fill or if the mud has kill mud during a well-control oper-
been contaminated with cement, ation while the pipe was not being
the mud or cement probably has worked or rotated. It is probably
set up. differentially stuck.
3. If the pipe sticks while making a 5. The pipe sticks while picking up or
connection or taking a survey. tripping, and it is still possible to
If the pipe can be rotated with rotate, circulate and move the pipe
restricted circulation, it is an indi- a limited amount. It is probably
cation of rocks, cement blocks or junk in the hole.
junk in the hole. 6. The pipe sticks suddenly while
If the pipe cannot be rotated with pulling out of the hole on a trip and
full circulation, it is probably cannot be worked up or down, with
differentially stuck. full circulation, and usually can be
rotated. It is probably key seated.

Methods and Procedures for Freeing Stuck Pipe

FREEING STUCK PIPE MECHANICALLY on page (15.23), is a quick way to esti-

When it is determined that the pipe is mate the depth of the stuck zone. To
differentially stuck or has been pulled increase the likelihood of success, the
into a key seat, the most successful spotting fluid should be applied as
method for freeing it is jarring down- soon as possible.
ward with drilling jars while torquing Plans should be made to mix and
the pipe. This should be started imme- spot a soak solution as soon as possi-
diately after the pipe sticks. Frequently, ble after differential sticking occurs.
this will free the pipe without the need Jarring should continue while this is
for spotting fluid. Time is critical, since being done.
the probability of freeing stuck pipe The soak solution to be used depends
Delays in diminishes with time. Delays in initiat- on several factors. When drilling with
ing jarring allow additional pipe to water-base muds, oil-base spotting fluids
initiating are preferred. If oil-base fluids present a
become stuck.
jarring allow NOTE: If, while running the pipe into the contamination or disposal problem,
additional hole, it becomes stuck due to undergauge alternative environmental spotting flu-
hole or changes in the BHA, it should not ids must be used. Often, oils, oil-base
pipe to mud, saturated saltwater, acids or surfac-
be jarred downward.
become tants can be used to spot and free stuck
stuck. FREEING STUCK PIPE WITH pipe, depending upon the situation. The
SPOTTING FLUIDS line of M-I PIPE-LAXT products is specially
Once it is determined that the drill- formulated for this purpose.
string is differentially stuck, the annu- PIPE-LAX can be mixed with diesel
lus should be displaced with a spotting oil, crude oil or kerosene to make
fluid from the bit to the free point. unweighted spotting fluids. For weighted
Surveys can determine the free point muds, PIPE-LAX can be mixed with
accurately, but running such surveys VERSADRILT or VERSACLEANT muds corre-
often takes a significant amount of sponding to the weight of the mud in
time. A pipe-stretch method, described the hole. This prevents the column of

Stuck Pipe 15.11 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

lighter spotting fluid from migrating run, the plugs were removed, and the
through the heavier drilling fluid and mud was removed without disturbing
maintains hydrostatic pressure. the filter cake. One cell was refilled
In environmentally sensitive areas, with oil and the other with a PIPE-LAX
where the use of oil-based materials oil-soak solution. Both cells were then
is prohibited, PIPE-LAX ENV, a water- placed on filter presses and pressurized
dispersible, low-toxicity spotting fluid, to 100 psi. The PIPE-LAX oil mixture
can be used. PIPE-LAX ENV is a single- cracked the filter cake rapidly and the
package spotting fluid that has proven lubricating mixture passed through the
to be highly effective in offshore appli- filter cake at a fast rate. Oil alone showed
cations around the world. It contains little cracking and the flow rate through
no petroleum oils, is compatible with the filter cake was much slower. Relating
most mud systems and may be used this to slurries spotted in a well, a higher
either weighted or unweighted. If frequency of success should occur with
a density greater than 9 lb/gal a PIPE-LAX oil solution than with oil
(1.08 SG) is required, PIPE-LAX ENV alone. Freeing of the pipe also can be
should be weighted with M-I BART or expected to occur in a much shorter
FER-OX T. Water should not be added to period of time with the PIPE-LAX
PIPE-LAX ENV slurry for any reason, oil-soaking solution.
since this will cause an undesirable
increase in viscosity.
The spotting The spotting method involves placing
method soaking solution adjacent to the stuck
zone. The most successful soaking solu-
involves tions to date have been PIPE-LAX with
placing diesel oil and PIPE-LAX W. Oil alone has
soaking been used for years with some measure
of success, but PIPE-LAX mixed with Figure 15: Cracking effect of filter cake using
solution diesel oil, VERSADRIL or VERSACLEAN has oil only (left) vs. PIPE-LAX and oil (right).
adjacent shown a much greater degree of suc-
to the cess. One gallon of PIPE-LAX is added Table 1 shows field data obtained
to each barrel of oil or oil-base mud from 178 cases of stuck pipe. The data
stuck zone. to be spotted. is arranged by the occurrences of stick-
The PIPE-LAX oil spotting technique ing in descending order and by the
is thought to work by altering the percent of the total each represents,
contact area between the filter cake illustrating when sticking is most likely
and the pipe. This is accomplished by to occur.
cracking the filter cake (see Figure 15). Statistical case history information
Although oil alone has been partially on a total of 247 cases of stuck pipe
successful, it is not as effective as a reveals that 203 were freed by spotting
PIPE-LAX oil spot. This can be attrib- a PIPE-LAX/oil soak solution. This rep-
uted to the increased filter-cake crack- resents an 82% success ratio in freeing
ing when PIPE-LAX is used. The filter the pipe. The time to free the pipe
cakes shown in Figure 15 were run on averaged 213 hr, with a large percent-
the same mud, using a standard API age freed in 2 hr or less. The average
filter cell containing a removable mud weight was 13.2 lb/gal, with the
drain plug located on the top of the heaviest being 18.2 lb/gal. In the latter
cell. Thirty-minute fluid losses were extreme, the pipe was freed in 45 min.

Stuck Pipe 15.12 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

_______________________ Operation Frequency % Total % Freed After Spot

Shut down 42 23.6 90.4
_______________________
Coming out of hole 33 18.5 90.9
_______________________ Going in hole 20 11.2 75.0
Making connection 18 10.1 100.0
_______________________
Wash pipe stuck 16 8.9 81.2
_______________________ Twist off 12 6.7 91.6
_______________________ Running casing 11 6.2 72.7
Drilling or reaming 11 6.2 81.8
_______________________ Lost circulation 7 3.9 57.1
_______________________ Gas or salt water 6 3.3 33.3
Other 2 0.56 100.0
_______________________
Total 178 100
_______________________
Table 1: Common causes of stuck pipe.
_______________________
SPOTTING TECHNIQUES Example:
_______________________ 500 ft of 6-in. collars
PIPE-LAX spotting fluids. Because of
_______________________ their greater contact area, drill collars in 978-in. hole
_______________________ become differentially stuck more fre- (0.06 bbl/ft)(500 ft) = 30 bbl
quently than the rest of the drillstring. 2. This volume should be increased
_______________________
Unless there is an indication from a enough to compensate for hole
free point survey or the pipe stretch enlargement and leave enough solu-
calculations that the pipe is stuck tion in the pipe so additional vol-
above the drill collars, spotting fluids ume can be pumped periodically to
usually are placed around the collars. compensate for migration of the
Preparing and placing a PIPE-LAX/oil spotted fluid. The extra volume
solution around the drill collar annulus usually ranges from 50 to 200% of
is relatively easy (placement of the soak the annular displacement volume,
solution when the drill pipe is stuck off depending on hole conditions.
bottom is discussed later). Regardless of 3. PIPE-LAX/oil solution is mixed by
where the drillstring is stuck, the vol- adding 1 gal of PIPE-LAX per barrel of
ume of the soak solution used should oil in the spot. The solution should
be sufficient to cover the complete sec- be mixed thoroughly before spotting.
tion of stuck pipe plus a reserve volume 4. Determine the pump strokes and
for periodically pumping an additional barrels of spotting fluid and mud to
Most failures volume of spot. Most failures occur be pumped to displace the entire
because the entire section of stuck drill collar annulus with soak solu-
occur because tion, leaving the reserve volume
pipe is not covered completely.
the entire The following procedure is recom- inside the pipe. Spot the slurry,
section of mended to free stuck drill collars: then shut the pump down.
5. After the PIPE-LAX/oil solution is spot-
stuck pipe is 1. Determine the volume of soak
ted, the pipe should be worked by
not covered solution required to fill the annular
putting it in compression. Slack off
space around the collars. The annular
completely. volume opposite the collars can be
10,000 lb below the weight of the
pipe and take 12 round of torque per
calculated by multiplying the annu-
1,000 ft with tongs or the rotary
lar volume (bbl/ft) by the length of
table. Release the torque and pick up
the collars (ft).
the 10,000 lb of weight. Repeat this

Stuck Pipe 15.13 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

_______________________ cycle about once every five minutes. M-I BAR systems is shown in Table 2.
_______________________ The pipe usually will come free on The formulation for mineral oil/FER-OX
the compression cycle. It should be systems is shown in Table 3. The mix-
_______________________
noted that working the pipe in ten- ing order for PIPE-LAX W is (1) oil, (2)
_______________________ sion or pulling 10,000 to 50,000 lb PIPE-LAX W, (3) water (stir this mixture
_______________________ over the indicated weight of the drill- for 30 minutes) then add (4) M-I BAR.
string could cause the pipe to become Formulation:
_______________________
stuck further up the hole in a key-seat The formulation charts are designed
_______________________ or dogleg. These hole conditions are to produce the minimum viscosity
_______________________ common at shallow depths. required to support weight material. If
_______________________
6. Periodically, pump 1 to 2 bbl of higher viscosities are required, increase
soak solution to keep the collars the concentration of PIPE-LAX W from
_______________________ covered. Continue to work the pipe 4.36 to 4.8 gal/bbl.
_______________________ as outlined above. Example:
_______________________ When premixed oil-base or invert oil To mix 120 bbl of 12 lb/gal PIPE-LAX W
_______________________ muds are available and the mud weight spot using mineral oil and M-I BAR:
is extremely high, PIPE-LAX can be From Table 2 calculate:
_______________________
added to these carriers and spotted. 1) Mineral oil ..................0.521 x 120 =
_______________________ Spotting this solution would be done 62.52 or 63 bbl
on a volumetric basis, since the PIPE-LAX 2) PIPE-LAX W.....................4.36 x 120 =
solution would weigh the same as the 523.2 gal or 10, 55-gal drums
drilling fluid. The advantage of using 3) Water ...........................0.203 x 120 =
this type of solution is that it will not 24.36 or 25 bbl
migrate while soaking. Mix for 30 min.
PIPE-LAX W spotting fluids. 4) M-I BAR: ........2.53 x 120 = 304 sacks
PIPE-LAX W may be mixed as a weighted
spot. The formulation for mineral oil/
Mud Weight Mineral Oil* Pipe-Lax W** Water M-I Bar
(lb/gal) (bbl) (gal) (bbl) (sacks)
8 0.528 4.36 0.345 0.34
9 0.527 4.36 0.309 0.88
10 0.526 4.36 0.272 1.44
11 0.525 4.36 0.236 1.99
12 0.521 4.36 0.203 2.53
13 0.515 4.36 0.172 3.08
14 0.507 4.36 0.142 3.62
15 0.496 4.36 0.117 4.17
16 0.484 4.36 0.092 4.71
17 0.469 4.36 0.071 5.24
18 0.453 4.36 0.050 5.78
** In diesel oil, it is recommended that the concentration of PIPE-LAX W shown in Table 2 be decreased from
4.36 gal/bbl to 3.5 to 4.0 gal/bbl. Diesel oil will inherently provide higher viscosities. If it is necessary to
reduce the viscosity of a PIPE-LAX W solution, dilute with oil or add 0.25 to 0.5 lb/bbl VERSAWET.T
** If higher viscosity is required, use 4.8 gal/bbl PIPE-LAX W.

Table 2: PIPE-LAX W formulation: mineral oil and M-I BAR (barite) (1 final barrel).

Stuck Pipe 15.14 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

Mud Weight Mineral Oil* Pipe-Lax W** Water Fer-Ox

(lb/gal) (bbl) (gal) (bbl) (sacks)
8 0.527 4.36 0.351 0.31
9 0.525 4.36 0.323 0.84
10 0.524 4.36 0.295 1.36
11 0.520 4.36 0.269 1.88
12 0.516 4.36 0.243 2.40
13 0.511 4.36 0.218 2.92
14 0.504 4.36 0.196 3.45
15 0.497 4.36 0.174 3.97
16 0.488 4.36 0.153 4.48
17 0.477 4.36 0.134 5.00
18 0.465 4.36 0.117 5.51
** In diesel oil, it is recommended that the concentration of PIPE-LAX W shown in Table 3 be decreased from
4.36 gal/bbl to 3.5 to 4.0 gal/bbl. Diesel oil will inherently provide higher viscosities. If it is necessary to
reduce the viscosity of a PIPE-LAX W solution, dilute with oil or add 0.25 to 0.5 lb/bbl VERSAWET.
** If higher viscosity is required, use 4.8 gal/bbl PIPE-LAX W.

Table 3: PIPE-LAX W formulation: mineral oil and FER-OX (1 final barrel).

PIPE-LAX ENV spotting fluids. 3. If the slurry is to be weighted, add
PIPE-LAX ENV spotting fluid is a low- the M-I BAR or FER-OX and blend
toxicity, non-petroleum solution for thoroughly. For densities above
use when oil or oil-base fluids are not 15 lb/gal (1.8 SG), add the required
permitted. It is a premixed solution, amount of LUBE-167and add weight
and needs only to be weighted to the as needed.
desired density. Care should be taken 4. Displace the annulus from the bit
not to contaminate PIPE-LAX ENV solu- to the top of the zone at which dif-
tions with either water or mud, since ferential sticking is suspected. Leave
this will result in excessive viscosity. at least 25 bbl (3.98 m3) inside the
Densities above 15 lb/gal (1.8 SG) require pipe to displace into the open hole.
additions of LUBE-167E to reduce final 5. Work the pipe while the spot is soak-
viscosity (see * Table 4). The following ing. Pump 1 to 2 bbl periodically to
is the procedure for using PIPE-LAX ENV: assure that fresh soak solution is
NOTE: Water contamination causes a being displaced into the open hole.
significant increase in PIPE-LAX ENV viscos- 6. Allow at least 24 hours for the
ity. After cleaning, all mixing pump and PIPE-LAX ENV to free the stuck pipe.
mud lines should be drained and then filled Generally, unweighted spotting flu-
with PIPE-LAX ENV before weighting up. ids are effective in a shorter period
1. Calculate the volume of spotting of time.
fluid required and add at least 10% to Procedure for spotting a light fluid
It is more compensate for any washout, plus at around the drill pipe. Occasionally,
difficult least 25 bbl (3.98 m3) to remain in the the drill pipe (rather than the drill col-
to spot the drillstring after initial displacement. lars) sticks. It is more difficult to spot
2. In a CLEAN, DRY tank, add the the soak solution around the drill pipe
soak solution required amount of PIPE-LAX ENV than around the collars because of
around the as determined in Table 4. Although hole enlargement. Since hole enlarge-
drill pipe some separation of materials may ment is not usually uniform, it is diffi-
because occur in the containers, transferring cult to calculate the volume of soak
the product into a pit will blend solution required to displace the
of hole the components, and product annulus to the right place.
enlargement. performance will not be affected.

Stuck Pipe 15.15 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

_______________________ Mixing Formulation (per final barrel)

Density Pipe-Lax Env M-I Bar Pipe-Lax ENV Fer-Ox
_______________________ lb/gal bbl lb bbl lb
_______________________ 8.5 1.000 1.000
9.0 0.982 28 0.985 26
_______________________ 10.0 0.943 83 0.955 79
_______________________ 11.0 0.905 139 0.925 132
12.0 0.868 194 0.895 184
_______________________
13.0 0.829 250 0.864 238
_______________________ 14.0 0.793 304 0.835 290
15.0* 0.754 361 0.804 343
_______________________
16.0* 0.717 415 0.774 395
_______________________ 17.0* 0.680 471 0.744 448
_______________________ 18.0* 0.642 526 0.714 500
* Higher-density PIPE-LAX ENV formulations may Suggested dilution concentrations are as follows:
_______________________
develop high viscosity and become difficult to Density LUBE-167 (% by volume)
_______________________ pump. This situation is aggravated by even small 15 - 16 15
amounts of water contamination. For densities 16 - 17 10
_______________________ greater than 15 lb/gal (1.80 SG), LUBE-167 should 17 - 18 15
be added to PIPE-LAX ENV formulations to reduce >18 20
_______________________ the final viscosity, then weighted to achieve the
desired density.
_______________________
Table 4: PIPE-LAX ENV/weighting material formulations.

The following procedure may be capacity. Length of the diesel column

used for spotting a lighter soak solu- can be determined by:
tion in a washed-out hole. This proce- Length of column = (drill pipe
dure involves alternatively pumping pressure/difference in gradient)
a given volume then measuring an The purpose of this step is to
annular differential pressure to calcu- determine more accurately the
late the depth of the leading edge of volume of the diesel oil inside the
the spot (see Figure 16). Any type of drill pipe instead of using what was
fluid with a weight different from that measured in the surface tank. It is
of the mud being used may be spotted not unusual to have a difference of
in the annulus by following these steps: 5 to 10 bbl due to the inability of
1. Check the weight of the fluid to be the pumps to get all of the liquid
spotted and determine its gradient from the tank or due to improper
(psi/ft). With the weight of the mud allowances for the line fill. If the
in the hole known, the difference volume of the diesel oil is greater
in the gradients of the two liquids than the capacity of the drill pipe,
can be established (for the purposes then omit Step 2 and rely on tank
of this description, it is assumed measurements only.
that diesel oil will be used as the 3. Check and mark the level of all mud
spotting fluid). Determine an pits before beginning the displace-
appropriate spot volume to cover ment with mud and the annular
the stuck zone. pressure measurement procedure.
2. Pump the diesel oil into the drill 4. Using the best estimate of the vol-
pipe. Shut down, then read the pres- ume of diesel spot inside the drill
sure on the drill pipe. It is assumed pipe, calculate the volume of mud
that the total volume of the diesel to be pumped so that the trailing
slug will not exceed the drill pipe edge of the diesel just clears the bit.

Stuck Pipe 15.16 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

Shut down the pump and close the Example:

annular preventers to measure the An 812-in. hole is being drilled with
1
annular differential pressure. Also 4 2-in. drill pipe and the pipe is stuck
check the mud pit level. Record with the bit at 10,000 ft. The pipe
these values in a tabular manner. is free at 7,300 ft. A 100-bbl slug of
The annular height of the diesel diesel oil is to be spotted, with the top
oil spot can be calculated by: of the slug near the stuck point (see
Length of column = (annular illustrations and steps in Figure 16).
pressure/difference Using the procedure outlined above:
in gradient) (1) Weight of diesel oil = 6.8 lb/gal;
gradient = 0.3536 psi/ft
The leading edge of the spot is now
Weight of mud = 10 lb/gal;
at a depth equal to the Total Depth
gradient = 0.5200 psi/ft
(TD) minus the length of column cal-
Difference in gradients =
culated above. Record these values.
0.5200 0.3536 = 0.1664 psi/ft
5. Pump a volume of mud equal to
(2) Approximately 100 bbl of diesel oil
the original spot volume minus any
are pumped into the 412-in. drill
observed mud loss in the pits. (This
pipe, the pump is shut down, and
assumes that all pit losses are diesel
the drill pipe pressure is 1,170 psi.
being lost in the open hole.)
(see Figure 16A)
6. Shut down the pump and close the
annular preventers to measure the Length of column = (1,170 psi/
annular differential pressure and 0.1664 psi/ft ) = 7,031 ft
check the mud pit level. Calculate The calculated length of a
the length of the column again. 100-bbl column in 412-in. drill
Record these values. pipe is 7,032 ft; therefore, it is
The depth of the leading edge of concluded that 100 bbl is the
the spot is calculated by subtracting actual volume in place.
each calculated length of the spot (3) Pit levels are marked.
column from the previous leading- (4) The diesel is displaced from the drill
edge depth. Keep a careful record of pipe by pumping the drillstring
_______________________ all measurements (volumes pumped, capacity volume (see Figure 16B)
_______________________ pressures, pit-volume changes) and and the annular pressure is 185 psi.
calculations. Length of column = (185 psi/
_______________________
The diesel oil spot can be moved 0.1664 psi/ft) = 1,112 ft
_______________________ up the annulus accurately to any The bottom of the column is at
_______________________ suspected stuck pipe joint by repeat- 10,000 ft
ing Steps 5 and 6 as many times The top is at 10,000 1,112 ft =
_______________________
as necessary. 8,888 ft
_______________________
The following cautions should be (5) There are no mud pit losses, so
_______________________ observed when using this method: the diesel spot is displaced by the
Corrections for the vertical height original volume, 100 bbl.
_______________________
of the column must be made when (6) The annular pressure is now
_______________________ 100 psi (see Figure 16C).
working in a directional hole.
_______________________ Displacement volumes should be Length of column = (100 psi/
measured accurately by using a 0.1664 psi/ft) = 601 ft
_______________________
pump-stroke counter and/or The bottom of the column is at
_______________________ 8,888 ft
measuring tanks.
_______________________ The mud weight needs to be The top is at 8,888 601 = 8,287 ft
_______________________ uniform throughout the system.

Stuck Pipe 15.17 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

It is noted that 10 bbl of mud have Length of column = (165 psi/

been lost from the pits; therefore, the 0.1664 psi/ft) = 992 ft
diesel spot is displaced by only 90 bbl The bottom of the column is at
instead of 100 bbl, as before. The annu- 8,287 ft
lar pressure is now 165 psi (see Figure The top is at 8,287 992 = 7,295 ft
16D) and the length of the column Since the stuck point is 7,300 ft,
is again calculated. the diesel has been positioned in
the desired area.

Drill pipe Annular Annular

pressure pressure pressure
1,170 psig 100 psig 165 psig
7,031
ft Annular
pressure
185 psig 992 ft

601 ft

1,112
ft

Procedure: 1. Spot diesel oil in drill pipe.

2. Measure pressure in drill pipe annulus accurately.
3. Move diesel slug in 100-bbl increments, calculating fluid column lengths.
4. Spot diesel oil at desired interval.
A B C D
Problem: Spot diesel oil Pump drillstring capac- Displace spot volume Displace another 100 bbl
at 7,300 ft ity volume to displace 100 bbl (NOTE: mud pit lost 10,
Approach: Pump 100 bbl 100 bbl diesel spot Read: Drill pipe so pump only 90)
diesel oil into from drill pipe pressure = 0 Read: Drill pipe
drill pipe Read: Drill pipe Annular pressure = 0
Measure pressure: pressure = 0 pressure = 100 psig Annular
Drill pipe = 1,170 psig Annular Diesel column length = pressure = 165 psig
Annulus = 0 pressure = 185 psig 100/.1664 = 601 ft Diesel column length =
Diesel column length = Diesel column length = Leading edge of spot: 165/.1664 = 992 ft
Pressure difference 185/.1664 = 1,112 ft 8,888 601 = 8,287 ft Leading edge of spot:
=
Gradient difference Leading edge of spot: 8,287 992 = 7,295 ft
1,170 10,000 1,112 = 8,888 ft Spot is properly placed
= 7,031 ft
.1664

Figure 16: Method for spotting pipe-freeing solution accurately in irregular hole.

Spotting hydrochloric acid to free 1. Pump a predetermined spacer of

stuck pipe in carbonate formations. approximately 10 to 30 bbl (generally
One technique One technique for freeing stuck pipe water or diesel).
for freeing in carbonate formations is to spot 2. Spot 20 to 50 bbl of 15% HCl
hydrochloric acid (HCl) opposite the around the suspected stuck zone.
stuck pipe stuck zone. HCl will react and degrade/ Allow at least 2 hr for the acid to
in carbonate dissolve the formation. The pipe/ react before the pipe is jarred. It is
formations formation contact area is reduced critical not to move the pipe during
and the pipe could be jarred free. this soak period. If the pipe is moved,
is to spot NOTE: High-strength pipe is subject to it could embed itself in the wellbore
HCl hydrogen embrittlement and catastrophic as the wall is eroded.
failure in acidic environments. If this pro- 3. An adequate volume of HCl should
cedure is attempted, the appropriate acid be left inside the drillstring to provide
inhibitors should be used. a second soak opportunity.

Stuck Pipe 15.18 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

4. Follow the HCl pill with the same 4. Differential pressure gradient =
spacer used in Step 1. 0.7800 - 0.3536 = 0.4264 psi/ft
5. When the pill is displaced from the 5. Annular length of diesel required =
hole, it can be incorporated into 500 psi
= 1,173 ft
the mud system. The HCl probably 0.4264 psi/ft
will be completely depleted and the 6. Volume of diesel required =
resultant pH can be adjusted using 1,173 ft x 0.05 bbl/ft = 58.7 bbl
soda ash, caustic soda or lime. 7. Spot the diesel in the annulus
Certain Certain precautions should be taken above the stuck zone.
precautions when spotting acid to free stuck pipe: II. To reduce the differential pressure
1. For safety reasons, diluting concen- by reducing the mud weight above
should be trated HCl should always be made the stuck point:
taken when by adding the acid to the water. 1. Assume 500 psi reduction in differ-
spotting acid Never add water to acid. ential pressure, 15 lb/gal mud
2. The pill should be circulated out weight, annular volume of 0.05
to free stuck through the choke at a slow pump bbl/ft and stuck point at 7,000 ft.
pipe rate, since carbon dioxide (CO2) gas 2. Convert the mud weight (lb/gal)
is generated when the acid reacts to psi/ft by:
with the carbonate formation and 15 x 0.052 = 0.7800 psi/ft
could behave like a gas influx. 3. Solve for pressure gradient (X) of
3. Use the proper safety equipment reduced mud weight by:
when handling HCl. (0.7800 - X) 7,000 = 500
4. Maintain enough caustic soda, soda 5,460 - 7,000X = 500
ash or lime on location to neutral- -7,000X = 500 - 5,460 = -4,960
ize the pill when it is circulated out X = 0.7086 psi/ft
of the hole. 4. Reduced mud weight =
0.7086
FREEING STUCK PIPE BY REDUCING = 13.63 lb/gal
DIFFERENTIAL PRESSURE 0.052
5. Volume of reduced mud weight
The reduction of differential pressure
spot: 7,000 ft x 0.05 bbl/ft = 350 bbl
also frees differentially stuck pipe. This
6. Spot the lighter fluid in the
can be accomplished in several ways.
annulus above the stuck zone.
One method is to spot a fluid that is
lighter than the drilling fluid in the Caution should always be exercised
hole above the stuck point. Water and when reducing the differential pressure.
oil are the most common fluids used If the differential pressure is reduced too
for this procedure. much, the well can kick. Contingency
Reduced-density fluids plans should be made in advance before
attempting these procedures.
I. If diesel oil is spotted, the following
procedure can be used: DRILL STEM TEST TOOL
1. Assume 500 psi reduction in dif- Another method used to free differen-
ferential pressure, 15.0 lb/gal mud tially stuck pipe by reducing the differ-
weight and annular volume of ential pressure is to use a Drill Stem Test
0.05 bbl/ft. (DST) tool. Although not as widely used
2. Convert the mud weight to a as the techniques discussed above, the
pressure gradient by: DST tool is considered to be opera-
15.0 x 0.052 = 0.7800 psi/ft tionally safe, since the well is kept under
3. Convert the weight of diesel to a strict control while differential pressure
pressure gradient by: is reduced across the stuck zone. The
6.8 x 0.052 = 0.3536 psi/ft

Stuck Pipe 15.19 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

Caution disadvantages of using this technique Caution should always be exercised

should are the time involved in mobilizing spe- when reducing the differential pres-
cial DST equipment and personnel, as sure. In this case, precise calculations
always be well as having to back off, run a caliper should be made to determine the vol-
exercised log (i.e. selecting packer seat) and mak- ume of light fluid to pump before
when ing a conditioning trip before the allowing the annulus to U-Tube. This
operation can be carried out. procedure should not be attempted
reducing the This procedure should be carried out with a small-nozzle bit in the hole due
differential only by an experienced technician to the possibility of plugging the bit.
pressure. who understands the entire procedure, The technique can be performed safely
appropriate tools and safety procedures. in most situations, provided it has been
After backing off above the stuck zone, thoroughly discussed and planned.
a caliper is run to select a near-gauge Consideration must be given to for-
zone for setting the packer. An appro- mation pressures and possible produc-
priate fishing assembly is run below the tive zones (gas/oil) above the stuck
packer, and the DST string is filled with point, as well as estimated or known
a lower-density fluid, depending on the formation pressures at the stuck point.
desired reduction in differential pres- If the formation pressure gradient is not
sure. The fishing assembly is attached known, then an approximate pressure
to the fish, and the packer is set to can be determined by multiplying a
relieve the hydrostatic pressure. The fish normal formation gradient (0.47 psi/ft)
may come free immediately, unseating times the stuck depth. This pressure,
the packer and causing a sudden subtracted from the mud hydrostatic
increase in hook load. If the packer is pressure, will give an approximation
unseated, the hydrostatic pressure is of the maximum pressure reduction
once again applied, causing another necessary to free the stuck pipe. The
overbalanced pressure situation. If the objective of this technique is to free
fish comes free, the packer should be stuck pipe prudently and safely
released and the pipe should be worked without losing control of the well.
up and down immediately. The following procedure is recom-
mended to free differentially stuck
U-TUBE TECHNIQUE
pipe if it has been determined that
Another method to free differentially the U-Tube technique can be applied
stuck pipe by reducing the differential safely and there are no known obstruc-
pressure is to reduce the height of the tions inside or outside the drillstring
mud column in the annulus to below to prevent fluid movement in either
the bell nipple. This procedure is direction (see Figure 17):
referred to as the U-Tube Technique. 1. Circulate and condition mud in hole.
In this procedure, mud is displaced 2. Determine a maximum safe
from the annulus by pumping a light hydrostatic pressure reduction.
fluid (such as diesel oil, water or nitro- 3. Calculate the following:
gen) down the drillstring. After pump- a) Total barrels of light fluid to be
ing the required volume of low-density displaced down the drillstring ini-
fluid, the pressure (and some liquid) tially that will ultimately reduce
is bled off the standpipe. The heavier hydrostatic pressure in both the
mud in the annulus is then allowed annulus and drillstring on
to U-Tube back into the drillstring, equalization of flowback.
resulting in a reduction in the height b) Maximum expected back-pressure
of the mud in the annulus. on the drill pipe gauge after this
volume has been displaced, due

Stuck Pipe 15.20 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

1 2 3
Before displacing After displacing After flowback
0 psi 1,494 0 psi
psi
Diesel Diesel
0 psi 0 psi Diesel 0 psi

6,796 ft 2,747 ft

Diesel
Air
Mud
Mud

Diesel
Mud
Casing Casing Casing

Mud
Mud
Mud

Mud
Mud

Mud
Mud
Stuck Mud Stuck Mud Free? Mud

TD TD TD

Figure 17: Sequence of U-Tube displacement to free differentially stuck pipe.

to differential pressure between the fluid from the drill pipe at a con-
the annulus and drill pipe. trolled rate through the choke or
c) Barrels of light fluid to be valve. Stop the back-flow periodically
flowed back to the pits during and observe the back-pressure on the
equalization. drill pipe and observe the annulus
d) Barrels of light fluid to be left in for any indication of upward fluid
the drillstring after equalization. movement. If the well is static (i.e. no
_______________________ e) Fluid level drop (ft) in the annu- formation fluid flow), the drill pipe
lus after the light fluid and mud pressure should decline with back-
_______________________
in the drillstring and mud in the flow. If the well is trying to kick, the
_______________________ annulus have equalized. drill pipe pressure will either stabilize
_______________________ 4. Rig up lines between the drill pipe or increase with back-flow. In the
and the rig floor manifold so the desired situation, the annular fluid
_______________________
lighter fluid can be displaced with level will continue to drop, simulat-
_______________________ the cementing unit. Also be pre- ing a vacuum during periods of back-
_______________________ pared or rigged up to control the flow. Continued observation of the
flow-back of light fluid through a annulus is very important in case it
_______________________
choke or valve during equalization. becomes necessary to abort back-
_______________________ 5. Displace the light fluid slowly down flow operations and implement
_______________________ the drill pipe until the total calcu- well-control procedures.
_______________________
lated volume has been displaced. 8. Work the pipe and jar on stuck
Note the back-pressure on the drill pipe, if possible.
_______________________
pipe gauge at this point. 9. If the drillstring does not come
_______________________ 6. Rig up to back-flow the light fluid. free, then:
_______________________ 7. Pull up to the maximum safe ten- a) Fill the annulus to the surface
sion for the drill pipe and back-flow with mud, slowly reverse the
_______________________

Stuck Pipe 15.21 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

_______________________ light fluid from the drill pipe, Total length of diesel in drill pipe:
_______________________ and circulate one full well vol- 96.5/0.0142 = 6,796 ft
ume. Observe the returns to see Length of 11.0-lb/gal mud in drill
_______________________
if any formation fluid (gas/oil) pipe: 13,636 6,796 = 6,840 ft
_______________________ has entered the wellbore. Hydrostatic pressure of diesel:
_______________________ b) Consider reducing the hydrosta- 6,840 x 0.3536 = 2,419 psi
tic pressure even further if it is Hydrostatic pressure of mud:
_______________________
deemed safe to do so, and repeat 6,796 x 0.5720 = 3,887 psi
_______________________ Steps 1 through 8. Hydrostatic pressure in drill pipe:
_______________________ 10. If the drillstring comes free, 2,419 + 3,887 = 6,306 psi
_______________________
then work the pipe and condition Back pressure on stand pipe
the hole before tripping and/or w/all diesel in pipe: 7,800
_______________________ drilling ahead. 6,306 = 1,494 psi
_______________________ Example (see Figure 17) given: Bottom-hole pressure after bleed-off:
_______________________ Total Vertical Depth (TVD) = 13,636 ft Annulus: 12,587 x 0.572 psi/ft =
Mud weight = 11.0 lb/gal, 11.0 x 7,200 psi
_______________________
0.052 = 0.5720 psi/ft Drill pipe: 2,747 x 0.3536 = 971 psi
_______________________ Diesel wt = 6.8 lb/gal, 6.8 x 0.052 = 10,889 x 0.5720 = 6,229 psi
_______________________ 0.3536 psi/ft 971 + 6,229 = 7,200 psi
Differential gradient = 0.5720 WASHING OVER PIPE
0.3536 = 0.2184 psi/ft AND SIDETRACKING
958-in. casing at 2,000 ft, Annular
If the pipe fails to come free after work-
volume = 0.0548 bbl/ft
ing and jarring for a reasonable period
Capacity of 412-in. drill pipe =
of time (usually 24 to 48 hr) with a soak
0.01422 bbl/ft
solution in the hole, the operator must
Hydrostatic pressure = 0.572 x
decide whether to attempt to back off
13,636 = 7,800 psi
above the stuck point and wash over
Purpose the stuck pipe, or plug back and side-
Reduce hydrostatic pressure at TD by track the hole. Usually, this decision is
600 psi to free stuck pipe. based on economics. The estimated
Procedure cost of a successful washover operation
Reduced hydrostatic pressure: is weighed against the cost of replacing
7,800 600 = 7,200 psi the stuck pipe plus the estimated cost of
Length of mud for 7,200 psi: redrilling to the same depth.
7,200/0.572 = 12,587 ft Wash pipe is made up of casing and
Mud column reduction for 7,200 psi: mill with an Outside Diameter (OD)
13,636 12,587 = 1,049 ft of less than that of the drilled hole,
Volume of 1,049 ft in annulus: 1,049 and an Inside Diameter (ID) greater
x 0.0548 = 57.5 bbl diesel (to be bled than the largest OD of the fish. Wash
off after flow-back) pipe is run into the hole on the drill
Length of diesel to be left in drill pipe. The amount of wash pipe run
pipe to balance annulus at 7,200 psi: at one time depends on the length
600/0.2184 = 2,747 ft of the fish to be washed over.
Volume of diesel in drill pipe for After circulation has been established,
600-psi reduction: 2,747 x 0.0142 = the wash pipe is rotated slowly over
39 bbl the fish. Minimum weight should be
Total volume of diesel required: applied and the amount of binding
57.5 + 39 = 96.5 bbl action observed in order to avoid
sticking the wash pipe.

Stuck Pipe 15.22 Revision No: A-0 / Revision Date: 033198

 CHAPTER

15 Stuck Pipe

Pipe-Stretch Estimate of Stuck Zone

CAUTION: Use the following procedure 7. Average these values as S for the
only after carefully evaluating the maxi- following equation:
mum safe tension for the weakest element 735,300 x WtDP x S
Depth =
in the drillstring and working limits of P
the drilling equipment. Where:
The following procedure for determin- Depth = Depth of free pipe (ft)
ing the depth of the stuck zone is accu- WtDP = Weight per foot, drill
rate enough to be used in vertical pipe (lb/ft)
wellbores. It is based on pulling up on S = Average pipe stretch (in.)
the stuck pipe and measuring the pipe P = Differential pull (lb)
stretch due to the change: This method is for vertical wellbores,
1. Fix a base point for measurement and is not applicable in highly deviated
that will not be changed by increased wells or wells with severe doglegs.
load on the derrick.
Example:
2. Attach a lath or strip of paper to the
drill pipe so that accurate stretch Drill pipe: 412-in., 16.60 lb/ft, Grade G
measurements can be marked from String weight: 154,000 lb (buoyed)
the base point. 1. Pick-up 160,000 lb to overcome
3. Pull sufficient tension to overcome the buoyed weight of drillstring and
weight of the pipe in the hole. Record mark pipe.
the weight-indicator reading and mark 2. Pick-up an additional 40,000 lb to
this point on the measuring strip as make the pipe stretch a measurable
Point A. amount.
4. Pull additional tension on the pipe, 3. Slack-off and repeat several times,
and then slack off to the same average values and calculate free
weight-indicator reading as recorded point.
when marking Point A. Mark the Average pipe stretch = 39.7 in.
measuring strip at this point as Point 735,300 x 16.60 x 39.7
Depth =
_______________________ B. The difference between the two 40,000
_______________________ marks is accounted for by friction in Depth = 12,115 ft
the sheaves and pipe in the hole. NOTE: The maximum allowable tension
_______________________
Draw a line midway between these for 412-in., 16.60 lb/ft, Grade G drill
_______________________ points, Point C, and use it as the pipe is 463,000 lb (no safety factor). The
_______________________ upper point of measurement. 200,000 lb (160,000 + 40,000) tension
5. Pull a predetermined safe tension used in this example is well below the
_______________________
in excess of the pipe weight and mechanical limits of the pipe.
_______________________
mark the pipe stretch and record
_______________________ the weight indicator reading.
_______________________ 6. Repeat Step 5 several times and
record the measured pipe stretch
_______________________
in each case.
_______________________

_______________________

_______________________

_______________________

_______________________

Stuck Pipe 15.23 Revision No: A-0 / Revision Date: 033198

CHAPTER

15 Stuck Pipe

Worksheet: Freeing Stuck Pipe

Stuck Pipe Mechanism (after Amoco TRUE)

Pipe Motion
Prior to Packoff/ Wellbore
Sticking? Bridge Differential Geometry
Moving up 2 0 2
Rotating up 0 0 2
Moving down 1 0 2
Rotating down 0 0 2
Static 2 2 0
Pipe Motion
After Sticking?
Down free 0 0 2
Down
restricted 1 0 2
Down
impossible 0 0 0
Pipe Rotation
After Sticking?
Rotate free 0 0 2
Rotate
restricted 2 0 2
Rotate
impossible 0 0 0
Circ. Pressure
After Sticking?
Circulation free 0 2 2
Circulation
restricted 2 0 0
Circulation
impossible 2 0 0
Totals
Instructions:
Answer the shaded questions by circling all the numbers in the row
with the correct answer.
Add the columns.
The column with the highest number indicates the most likely
sticking mechanism. See freeing action tables on next page.

Stuck Pipe 15.24 Revision No: A-0 / Revision Date: 033198

 CHAPTER
15
Stuck Pipe

Stuck Pipe
Freeing Wellbore Geometry Freeing Packoff/Bridge Freeing Differential Sticking
Initial action: Stuck while moving up or Initial action:
If sticking occurred while mov- with string static Stuck while moving down Circulate at normal rate.
ing up, apply torque and jar Action to establish circulation: Action to establish circulation: Work MAXIMUM limit torque
DOWN with max. trip load. Apply low pump pressure (200 Apply low pump pressure (200 down to the stuck depth and
If sticking occurred while mov- to 400) psi. Maintain pressure if 400) psi. Maintain pressure if hold the torque in the string.
ing down, do not apply torque restricted circulation is possible. restricted circulation is possible. Stop or reduce pump speed to
and jar UP with max. trip load. DO NOT JAR UP!! APPLY DO NOT JAR DOWN!!! APPLY minimum.
Stop or reduce circulation when TORQUE!!! Slack-off to TORQUE!!! Apply MAXIMUM Slack-off MAX. set down limit!
cocking the jar and when jarring MAXIMUM set down weight. overpull to jar. Allow sufficient
down. Allow sufficient time for a time for a hydraulic jar to trip Allow sufficient time for a hydrau-
hydraulic jar to trip (4 to (4 to 8 min for long cycle, lic jar to trip (4 to 6 min for long
NOTE: Pump pressure will cycle, see jar manual).
INCREASE the hydraulic jar 6 min for long cycle, see jar manual).
up-blow, and DECREASE the see jar manual). If the string does not come free,
down-blow. If the string does not come free, If the string does not come free, hold torque in the string and
DO NOT JAR UP!!! Jar DOWN DO NOT JAR DOWN!!! Jar up continue jarring down with
15.25

Continue jarring until the string max. trip load.

is free or an alternative decision until the string comes free or until the string is free or an
is made. Jarring for 10+ hours an alternative decision is made. alternative decision is made. If the string does not come free
may be necessary. Jarring down for 10+ hours Jarring up for 10+ hours may after 5 to 10 jars blows, continue
may be necessary. be required. jarring while preparing a pipe
Secondary action: releasing pill.
Spot acid if stuck in limestone When circulation is established: When circulation is established: Secondary action:
or chalk. Spot fresh water with
mobile salt. Slowly increase pump speed to Slowly increase pump speed to Mix and spot a PIPE-LAX soaking
Revision No: A-0 / Revision Date: 033198

max. rate. When possible, work max. rate. When possible, work solution as soon as possible.
When the string comes free: the string and circulate the the string and circulate the hole
Increase circulation to max. rate, hole clean from bit depth. clean from bit depth. When the string is free:
rotate and work the string. Rotate and work the string.
Ream the section until the hole Ream the section until the hole
Ream/back ream the hole is clean. is clean. Circulate to clean the hole.
section thoroughly.
If POOH to log and/or run Continue RIH, staging-in and cir- Condition mud to
Circulate the hole clean. casing, return to bottom and culating bottoms up. If excessive appropriate properties.
circulate the hole clean. set down weight is observed,
stop and circulate the hole clean.
Ream as needed.

(After Amoco TRUE.)

 CHAPTER
15
Stuck Pipe

Stuck Pipe Hole Packoff

Stuck Pipe
Unconsolidated, Cement
Problem Settled Cuttings Shale Instability Fractured Formation (Blocks or Soft) Junk in Hole
Causes - Drilling too fast - Drilling reactive shale - Drilling uncemented - Cement blocks fall - Accidental junk falling
- Inadequate annular - with non-inhibitive mud - formation - from around casing - in hole
velocity or rheology - Drilling pressured shale - Little or no filter cake - shoe, squeeze plugs or - Downhole equipment
- Cuttings accumulation - with insufficient mud - Drilling naturally - sidetrack plugs - failure
(washouts) - weight - fractured formation - Attempt to circulate
- Not enough - while the drillstring is
- circulating time - immersed in soft cement
- Drilling blind without - (flash set)
sweeps
- Drilling without
circulating
Warning signs - High ROP with poor - Increase in FV, PV, YP, - Solids-control equipment - Excessive casing rathole - May occur any time
and indications - cuttings return - gels and CEC - loaded with sand - Increase in torque - Metal parts at the shakers
- Increase in torque, drag - Increase in torque, drag - and cuttings - and drag - Partial motion is possible
and pump pressure - and pump pressure - Seepage losses - Circulation restricted
15.26

- Overpull on connection - Overpull on connection - Fill on connections and - Restricted pipe movement
and when tripping - and when tripping - after tripping
- Fill on bottom after - Bit and BHA balling - Sudden increase in torque
connection and trips - Pore pressure increase - and drag
- Circulation restricted - Fill on connection and - Circulation restricted
- Increase in LGS and - after trips - Large caving at shakers
- mud weight - Large cavings at shakers
- Circulation restricted
Revision No: A-0 / Revision Date: 033198

Prevention - Proper mud rheology - Use inhibitive mud - Provide good filter- - Limit casing rathole - Use good practices
- Use maximum GPM - Increase the mud weight - cake quality - Allow sufficient time - Keep hole covered
for hole size - Minimize open hole - Use appropriate - for cement to set - Check downhole tools
- Control ROP if needed - exposure time - bridging materials - Reduce tripping speed - on regular basis
- Pump sweeps to clean - Use sweeps to clean - Avoid excessive - opposite cement section
the hole - the hole - circulating time - Calculate top of cement
- Wiper trip after - Increase mud rheology - Use sweeps to keep the - and start circulate two
motor runs - hole clean - stands above
- Increase drillstring - Increase mud rheology - Control drilling in
rotation - soft cement
- Circulate longer

(After Amoco TRUE.)

 CHAPTER
15
Stuck Pipe

Stuck Pipe Well Geometry/Differential

Stuck Pipe
Problem Key Seating Undergauge Hole Stiff Assembly Mobile Formation Doglegs and Ledges Collapsed Casing
Causes - Drill pipe wears a key- - RIH with a full-gauge - BHA change from - Drilling plastic salt - Drilling hard/soft - External formation
seat in the formation - bit and BHA in an - limber to stiff cannot - or shale formation - interbedded - pressure (often
- Often associated with - undergauge hole - tolerate changes in - formation - opposite plastic
doglegs - angle and direction - Frequent change in - formation) exceeds
- Drill collars jam into - hole angle/direction - casing strength
the narrow groove of - Drilling fractured/ - Failed cement
keyseat - faulted formation
- High dip angles
Warning signs - Severe dogleg section - Undergauge bit - New BHA is run - Increase in torque - Overpull on connec- - Drilling plastic
and indications - Pipe rotating at the - pulled out - in hole - and drag - tions and trips - formation
same spot for - Tight hole - Presence of doglegs - Overpull when - Increase in torque - Cement chunks
extended period - Sudden loss of - Sudden loss of - tripping out of hole - and drag - Lost circulation
of time - string weight - string weight - Tight hole
- Tight hole - inside casing
Prevention - Minimize - Gauge old and - Minimize BHA - Maintain sufficient - Minimize sharp and - Use proper casing
15.27

dogleg severity - new bits - changes - mud weight - frequent wellbore - strength opposite
- Wiper trip/ream - Ream last three joints - Limit dogleg severity - Select the proper - course changes - plastic formation
dogleg sections - at least to bottom - Plan a reaming trip - mud system - Avoid prolonged
- Use keyseat wiper - Never force bit - if a stiff BHA will - Frequent reaming/ - circulation opposite
or reamer - through tight - be used - tripping - soft formation
spots, ream - Use eccentric bit - Minimize BHA
- Minimize open hole - changes
exposure time
Revision No: A-0 / Revision Date: 033198

Problem Differentially Stuck

Causes - The hydrostatic pressure exceeds - Porous, permeable formation - Thick, poor quality filter cake
formation pressure - High fluid loss - Pipe stationary too long
Warning signs - Circulation is not restricted when stuck - Drilling with high overbalance - Overpull opposite porous formation
and indications - Increase in torque and drag - Poor filtration properties - Hole sticky on connection
Prevention - Minimize overbalance - Minimize area of contact by using - Improve filter-cake quality
- Control downhole filtration - heavy-weight drill pipe and spiral collars - Minimize coefficient of friction, use lubricant
- Minimize time pipe is stationary - Maintain optimum hydraulics - Use proper bridging agents
- Proper casing design - Minimize drill solids content