ROTARY DRILLING SERIES
Unit I:
The Rig and Its Maintenance
Lesson I: Lesson 2: Lesson 3: Lesson 4: Lesson 5: Lesson 6: Lesson
r
Lesson 8: Lesson 9: Lesson 10:The Rotary Rig and Its Components The Bit
Drill String and Drill Collars
Rotary, Kelly, Swivel, Tongs, and Top Drive The Blocks and Drilling Line
The Drawworks and the Compound
Drilling Fluids, Mud Pumps, and Conditioning Equipment Diesel Engines and Electric Power
The Auxiliaries Safety on the Rig
Unit II: Normal Drilling Operations
Lesson I: Making Hole
Lesson 2: Drilling Fluids
Lesson
r
Drilling a Straight Hole Lesson 4: Casing and Cementing Lesson 5: Testing and CompletingUnit III:
Nonroutine Operations
Lesson I:
Lesson 2: Lesson 3:
Controlled Directional Drilling Open-Hole Fishing
Blowout Prevention
Unit IV:
Man Management and Rig Management
Unit V: Offshore Technology
Lesson I: Lesson 2: Lesson 3: Lesson 4: Lesson 5: Lesson 6: Lesson
r
Lesson 8: Lesson 9: Lesson 10:Wind, Waves, and Weather Spread Mooring Systems Buoyancy, Stability, and Trim
Jacking Systems and Rig Moving Procedures Diving and Equipment
Vessel Inspection and Maintenance Helicopter Safety and Survival Procedures Orientation for Offshore Crane Operations Life Offshore
ROTARY DRILLING
OPEN-HOLE
FISHING
Unit III • Lesson 2
Third Edition
Edited by Jean Trimble Pietrobono
Published by
PETROLEUM EXTENSION SERVICE
Division of Continuing Education The University of Texas at Austin Austin, Texas in cooperation with ~ INTERNATIONAL ASSOCIATION ~ OF DRILLING CONTRACTORS Houston, Texas 1988
PREFACE
This second lesson in Unit III of the Rotary Drilling Series introduces the
reader to the tools and techniques of open-hole fishing. The lesson covers the major causes of fishing jobs; basic steps in fishing out a twistoff, stuck pipe, wireline, or junk lost in the hole; and the economics of fishing.
Research for this third edition of Open-Hole Fishing was done by David J.
Morris of the Petroleum Extension Service staff. Gore Kemp, Vice President of PETCO Fishing and Rental Tools, reviewed the text and illustrations. His generous contribution of time and expertise to ensure the accuracy of this publication is greatly appreciated. Thanks also are extended to Michael C.
Brown of Bowen Tools, Inc., Derrel D. Webb of Houston Engineers, Inc., T. J.
. I ! I - - - IMPERMEABLE FORMATION D 0 PERMEABLE FORMATION IMPERMEABLE FORMATION DIFFERENTIAL PRESSURE
-r---\--===:::::---MUD LIQUIDS / ' MUD CAKE-~ ___FIGURE 10. WALL-STUCK PIPE
Differential sticking. Many fishing jobs are caused by drill pipe or collars becoming differen-tially stuck, or wall stuck (fig. 10). Wall sticking commonly occurs in a permeable, low-pressure formation where the hydr~static pressure of the drilling mud forces mud liquids into the forma-tion and causes a buildup of mud solids known as
mud cake or filter cake. The pressure of mud in
the annulus presses the pipe against the mud cake lining the hole. This pressure may be strong enough to support the entire drill string. The longer the drill string remains motionless, the more likely it will become wall stuck and the harder it will be to free. Excessive hydrostatic pressure may be responsible, but only a fairly small overbalance, or pressure differential, from wellbore to formation is necessary for wall stick-ing to occur. The more solids that are in the mud, the thicker the mud cake ""ill be-and the tighter the pipe will be stuck.
If the pipe becomes stuck while motionless in a clean, well-conditioned hole and circulation can be stopped and then resumed at the original
pressure, chances are that the pipe is wall stuck. Prompt action, such as immediately rotating the drill string, may dislodge wall-stuck pipe that cannot be pulled free. Oil spotting (pumping a slug of oil-based fluid down the drill stem and up the annulus to the stuck point) may break the mud seal. If these actions do not free the pipe, a ~ fishing job may become necessary. Using spiral drill collars and heavyweight drill pipe, each joint of which has a large external upset in its center, can help prevent wall sticking.
Offshore Sheared Pipe
When a floating offshore drilling rig must quickly leave the well site because of unexpected rough weather or other hazards, standard pro-cedure is to close the subsea blowout preventer pipe rams and sever the drill string. The sheared pipe still attached to the drill string must later be retrieved, using special fishing procedures, before normal drilling operations can continue. In effect, shearing the drill string intentionally creates a fishing job, but for the purpose of preventing a blowout.
Junk in the Hole
Smaller fish, or junk, lost in the hole may
include-1. bit cones, bearings, or other parts lost when a bit breaks;
2. broken reamer or stabilizer parts; 3. metal fragments lost in a twistoff;
4. metal fragments produced by milling the top of a fish to aid in its retrieval;
5. naturally occurring pieces of hard, crystal-line, or abrasive minerals such as iron pyrite; 6. tong pins, wrenches, or other items that fall into the hole because of rig equipment failure or by accident;
7. equipment such as packers, core barrels, and drill stem test (DST) tools that become lodged downhole; and
8. wireline tools and parted wireline.
;e
Preparing for a
:h
d
Fishing Job
)f
When it becomes necessary to fish drilling equipment out of an uncased hole, the experi-enced operator finds out as much as possible about the situation before taking action. Among the questions he may attempt to answer are the following:
e 1. What is to be fished out of the hole?
T. 2. Is the fish stuck, or is it resting freely?
3. If stuck, what is causing it to stick? 4. What is the condition of the hole?
,f 5. What are the size and condition of the fish?
e 6. Could fishing tools be run inside the fish, or
must they be run outside it?
7. Could other tools be run through the fishing assembly that is to be used?
8. Are there at least two ways to get loose from the fish if it cannot be freed?
A 4,000 FT - OF PIPE SET BACK 10,000 FT 6,000 FT
In a fishing job involving the drill stri operator can often ascertain whether or lost drill pipe is stuck in the hole by deter what happened just before it was lo~ instance, if the bit was on bottom and ( and if there was no sudden, unexplained i
of torque or decrease in rotary speed bef drill string broke, the most likely explan the occurrence of a twistoff, and the pip( bably not stuck. If, however, the pi] motionless in the hole or if it was being r, lowered but not rotated, it is probably either mechanically or differentially.
The operator must determine, as accur possible, the depth at which the top of a off drill string can be found. The upper of the string is measured as it is remOVl the hole. If the bit was on bottom when' string broke, or if the drill string becarr off bottom, the length of the upper par same as the measured depth of the top of (fig. 11). B 2,000 FT -OF PIPE SET BACK AFTER BREAK 5,000 FT
1
3,000 FT1
FIGURE 11. FINDING THE DEPTH OF THE TOP OF THE FISH IF (A) THE BIT WAS ON BOTTOM WHEN THE DRILL STRING BR
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•
-
/1,
IFIGURE 16. DITCH MAGNET (COURTESY OF BOWEN TOOLS,
INC.)
mud pit to capture most cuttings from the mill-ing operation (fig. 16). Removal of cuttmill-ings reduces wear on mud pumps and other equip-ment.
Once the top of the fish has been milled fairly smooth, the operator makes up afishing string. A typical fishing string consists of, from bottom to top, an overshot, a bumper sub, a hydraulic jar, and a jar accelerator made up on drill pipe (fig. 17). To calculate how much pipe and how many collars he needs to reach the fish, the op-erator must consider.the made-up length of the fishing tool assembly, as well as the distance the fish must travel inside the assembly before it can be firmly caught.
A typical circulating and releasing overshot consists of three outside parts: a top sub, a bowl, and a guide (fig. 18). The top sub connects the overshot to the fishing string. The bowl may be
t fitted with different types of equipment to grasp
f the fish and different guides to help center the
fish beneath the tool.
The overshot must have an external diameter that allows proper clearance in the hole, and the grapples must be close to the size of the fish. If
the diameter of the fish is close to the maximum catch size for the overshot, a spiral grapple is used (fig. 19). If tlH' fish diameter is well below the maximum catch size, a basket grapple as-sembly is installed (fig. 20). A basket grapple assembly maul' up with a mill control packer can be used to dress the top of a mildly distorted or burred fish so that it can be caught firmly by the grapples. Both tYVes of packers seal around the
- -17
ACCELERATOR?!!-:.!
I
-FIGURE 17. SIMPLF: FISHING ASSEMBLY
TOP SUB
BOWL
GUIDE
FIGURE 18. OVERSHOT (COURTESY OF BOWEN TOOLS, INC.)
fish, allowing drilling fluid to be pumped down to clean out the bottom of the hole.
The operator runs the fishing string to within a few feet of the top of the fish. He starts circu-lation to clean cuttings and settlings off the top of the fish and to clean out mud cake that may have accumulated inside the overshot. He then lowers the fishing string slowly to touch the top of the fish and establish its exact depth. When the fish has been tagged, hook load decreases; the position is marked on the kelly. The string is
FIGURE 19. OVERSHOT HAVING SPIRAL GRAPPLE (COURTESY
OF BOWEN TOOLS, INC.)
FIGuRE 20. OVERSHOT HAVING BASKET GRAI'PLF: (COURTESY
Before being run in, the knuckle joint is manually
forced off center to make sure the lip on the
wall-hook opening faces about 90° away from the angle of the knuckle joint so that it will touch the fish. Spacer washers between the top sub and
the knuckle joint are used to face the opening
cor-rectly.
The knuckle joint is kicked off by running in a restriction plug and establishing circulation. However, good practice is to run the tool in with the restriction plug in place, because the pipe could become wall stuck in the time it takes the plug to drop to the knuckle joint. The joint is kept straight by running it in without circulation; it is then kicked off in the washout by starting the pumps.
With the knuckle joint bent, the fishing string is rotated slowly to make a sweep around the
cavity. If it does not touch the fish, the string is
then lowered a few more feet and again rotated. When the wall hook tags the fish, the string torques up and the knuckle joint tends to straighten. The string is slowly raised; when the fish slips into the wall-hook opening, torque is released suddenly. The overshot can then be lowered to engage the fish, and the fish can be removed from the hole.
. Fishing for Stuck Pipe
As mentioned earlier, there are two main ways that pipe can become stuck in the hole: mechanical sticking by solid materials and differ-ential sticking by fluid pressure. Keyseating is a special type of mechanical sticking that happens when the pipe becomes stuck during a trip. Although differential sticking is the most com-mon reason for stuck pipe, fishing techniques are somewhat limited for recovering differentially stuck, or wall-stuck, pipe. Emphasis is therefore placed on preventing wall sticking from the start.
Freeing Mechanically Stuck Pipe
After a fish has been caught in the overshot, the usual procedure is to circulate out the settled
cuttings without rotation. If circulation cannot
be fully established and the fish cannot be pulled, the fish is almost certainly stuck mechanically in the hole.
Jarring. The situation described calls for the use of a hydraulic jar and a J'ar accelerator (figs. 25 and 26). The weight of the drill collars is
,~ ; U 1 i i :;
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,~, : lFIGURE 25. HYDRAULIC JAR
.1
FIGURE 26. JAR ACCELERATOR
put to bear on the fish to cock the hydraulic jar. A moderate pull is then taken to stretch the fishing string, compressing an inert gas or liquid in the jar accelerator above the drill collars. At the same time, oil in the hydraulic jar begins to seep between a piston and a cylinder. The cylinder restricts the first few inches of travel, but once the piston is pulled past the restricted length of the cylinder, there is little restraint. The stretch in the drill string, aided by the compressed gas
or liquid in the jar accelerator, snaps the jar's piston and the drill collars upward. The mandrel knocker strikes the knocker sub with great force, jarring the stuck fish upward. Weight is again applied to the string to recock the jar for another blow. Jarring is continued until the fish is free
and circulation can be restored.
Finding the stuck point. If jarring does not free the fish, the operator must determine at what point in the hole the fish is stuck. The most
reliable way to do this is to use a free-point
indi-cator (fig. 27). This device, consisting of a tool
'...H--ELECTRIC ,r CABLE o o .; ... TOOL JOINT :1.0""' LOCATOR o o 'F'!' .'.~
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~;FIGURE 27. FREE-POINT INDICATOR AND STRING SHOT
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into the hole on drill pipe and run to within 10 feet of the top of the fish. Circulation is estab-lished, and the washover pipe is lowered slowly over a joint or two of the fish left standing as a guide. Once it is determined that the washover pipe is going over the fish, rotation and washing over can begin.
The washover string is rotated at 30 to 50 rpm, depending on how tightly the fish is stuck. Rotation and circulation are stopped every 20 to 30 feet to check for torque buildup and friction
in the washover string. If torque becomes too
great, it may be necessary to come out of the hole and remove part of the washover pipe. In a crooked hole, the top of the fish may be lying under a bend; the shortened washover pipe can conform more easily to the curvature of the hole (fig. 32).
When the entire washover pipe has washed over the fish, the fish is engaged. An upward
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c, c o • 0 o 0 °0 co C • 0 , o 0 c..
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o ' o o • 0 o ' • a • o .J J o 0 o 0 o • , J • J, c o o o J 0FIGURE 32. EFFECT OF SHORTENING WASHOVER PIPE IN A
CROOKED HOLE
pull on the fishing string indicates whether the rest of the string below the washover pipe is free
and can be pulled. Ifit is not free, a string shot is
run down inside the drill string and fish to within a joint or two of the bottom of the washover pipe. Left-hand torque is applied, the string shot is detonated, the freed pipe backed off, and the fish brought to the surface and stripped out of the washover pipe.
Stripping the fish out of the washover pipe can be a long, hard job. The drill pipe and part of the fishing string are pulled, broken out, and set back until the washover pipe is in the rotary table and the slips are set around it. A split-slip holder, or
bowl, is screwed into the threads in the top of
the washover pipe, and split slips are set around the fish to hold it. The backed-off fish is stripped out of the washover pipe with the elevators. Finally, the washover pipe can be pulled, if necessary, to change the rotary shoe.
To retrieve the remaining stuck fish, the washover pipe is again returned to bottom. This sequence of operations (washover and pulling) is repeated until all of the fish is retrieved. The last section of the fish is stripped out until the bit is pulled up near the bottom of the washover pipe.
If the bit is too large to pass through, the fish
and washover pipe must be pulled, suspended, and broken out together, a complicated and labo-rious procedure: double stripping 500 feet of washover pipe takes about 4Ifz hours.
If the fish is stuck off bottom, a 'waslwver
back-off connector may be added to the washover string
(fig. 33). A washover back-off connector is made up in a length of washover pipe to engage the top of the fish after the washover pipe has washed over and freed part or all of it. The washover back-off connector is stabbed down the upper-most joint of washover pipe until the threads on the connector tool (sub) mate with the washover pipe threads.
Drilling out. Sometimes after backing off above the stuck point and pulling the freed sec-tion, the inside bore of the fish still in the hole becomes plugged by settlings or cavings, making it impossible to run a free-point indicator and
OVERRIDING ~--CLUTCH ~\",,""_ _ FISHING STEM PISTON ";'--FISHING STEM OO,l¥---S PRING WASHOVER SAFETY JOINT WASHPIPE CONNECTOR - -.. ---el.--SHEAR PIN ~ ~__i-j---SAFETY JOINT " ~ . -f4-_ _ FISHING PIN CONNECTOR
FIGURE 33. WASIIOVER RACK-OFF CONNECTOR
string shot (fig. 34). Should this happen, a drillout tool can be used to reopen the fish (fig. 35). The drillout tool is run to the top of the
restricted tish and made UlJ on it.
FIGURE 34. FISH PLUGGED WITH CUTTINGS OR CAVINGS
A special hex kelly tipped with a junk mill is run in on wireline and inserted through a self-aligning bushing built into the kelly drive. Rotating the fishing string causes the kelly and mill to also rotate. Pump pressure forces the mill into the fish and washes out the cuttings. When the kel1y has drilied all the way down, drilling fluid exits through the side opening, or tattletale, causing pump pressure to drop.
If more debris must be removed, the kelly is retrieved by wireline, and a short length, or pup
)oint, of drill pipe is made up between the kelly and mill. This assembly is run back into the tool, and milling is resumed until the debris is removed. Finally, the mill and kelly are again retrieved by wireline, leaving the outer case of the drillout tool attached to the fish. The rest of the fish is then removed using standard back-off procedures.
Cutting pipe. Backing off at a tool joint is usually preferable to cutting pipe because it leaves a clean tool joint box in good condition "looking up" - that is, facing uphole - so that it can be easily screwed into or engaged by the fishing string. However, hole obstructions or pipe damage may make it impossible to back off at a connection. If the fish cannot be pulled or jarred loose, cutting the pipe between tool joints may be the only way to retrieve it. Both outside and inside cutters are available for this job.
If a fishing tool must be run that will not allow a free-point indicator and string shot for a normal backoff to pass, a mechanical or hydraulic outside cutter may be run on the bottom of a washover pipe string far enough to get below the obstruc-tion (fig. 36). After the cutter has been lowered over the fish to the desired depth, it is raised until slips, pawls, or (as in fig. 36) spring dogs engage a tool joint. If the cutter is mechanical, the driller takes a strain on the fishing string, caus-ing the knives to move into cuttcaus-ing position. The tool is rotated slowly under strain until the pipe has been cut in two. A hydraulic cutter uses pump pressure to energize the piston and move the knives into cutting position. The washover pipe, cutter, and plugged part of the fish are then pulled from the hole.
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. ~'" ... '.: \ :'" ' ' ~:. • ~ ' . : : :~\' '. ,-' , ' _" I' :FIGURE 36. CUTTING FISH USING OUTSIDE CUTTER
If the stuck pipe turns in the hole, applying torque for a string shot back-off becomes impos-sible, and a mechanical cutter may simply engage the fish without cutting it. This situation may call for either a )et cutter or a chemical cutter (fig. 37).
The cutter is lowered inside the fish on a wire-line to a depth of about one or two joints above the stuck point. The jet cutter blasts a shaped charge. an explosive device that focuses the energy of its detonation in one direction, to cut the pipe in two. The force of the blast usually flares the pipe, which must then be trimmed before it can be caught. The chemical cutter forces high-pressure jets of chemicals at high speed and temperature thwugh small openings in the tool
:0
sever the pipe. One advantage ofREVIEW QUESTIONS
LESSONS IN ROTARY DRILLING
Unit III, Lesson 2: Open-Hole Fishing
1. _ _ Twistoffs are usually caused by excessive rotary torque. (True or False) 2. _ _ Surface signs of a twistoff may
include-A. increased drill string weight.
B. increased pump pressure. C. increased pump speed. D. increased drilling torque.
3. _ _ Pipe sticking caused by fluid pressure is called-A. sloughing.
B. twistoff. C. keyseating.
D. differential sticking.
4. _ _ Which of the drawings below illustrates pipe stuck in a sloughing hole?
A B
c
I I -- . ~:=: -F= r-;;;;::=-=::: = ----= -
O~
~ --l-5. _ _ If the drill string parts while the bit is on bottom and rotating, the most likely cause is wall sticking. (True or False)
6. _ _ A driller has set back 19 stands (1,710 ft) of drill pipe while tripping out of a 7.260-ft hole. The drill string becomes wall stuck and parts. The driller then trips out 4,185 ft of pipe above the break. How long is the fish?
A. 1,365 ft B. 1,710 ft
C. 3,075 ft
7. _ _ In question 6, if the fish does not fall, at what depth will the top of the fish be found? A. 3,075 ft
B. 4,185 ft C. 5,895 ft
D. 7,260 ft
8. _ _ If an impression block shows the top of a twisted-off section of drill pipe to be badly -distorted, what is the fishing tool most likely to be run first?
A. an overshot B. a string shot C. a mill
D. a releasing spear
9. From bottom to top in the hole, what is the correct order of tools on a typical fishing string?
A. overshot, bumper sub, jar accelerator, drill collars, hydraulic jar B. overshot, bumper sub, hydraulic jar, drill collars, jar accelerator C. jar accelerator, hydraulic jar, bumper sub, overshot, drill collars
D. hydraulic jar, drill collars, jar accelerator, bumper sub, overshot 10. Which of the following fishing tools engages a fish from the outside?
A. an overshot B. a jar accelerator C. a taper tap D. a releasing spear
11. _ _ With its restriction plug in place, a knuckle joint is run into the hole with no circulation. (True or False)
12. _ _ The tool used to locate where pipe is stuck is the-A. hydraulic jar.
B. string shot.
C. washover back-off connector. D. free-point indicator.
13. _ _ The fishing procedure used to clean debris out of the annulus is called-A. milling.
B. backing off. C. washing over. D. jarring.
14. _ _ In backing the drill string out of a length of stuck pipe, the string shot should be fired-A. one or two joints below the stuck point.
B. as close as possibe to the stuck point. C. one or two joints above the stuck point. D. about ten joints below the surface. 15. A drillout tool is
used-A. to clean out the inside bore of a fish plugged with cuttings or cavings. B. to enlarge the hole to allow retrieval of a bit.
C. to obtain a core or to retrieve junk embedded in the hole bottom. D. to sidetrack a fish.
16. In general, it is usually better to back off a stuck drill string at a tool joint than to cut
pipe. (True or False)
17. To cut stuck pipe that turns easily in the hole, ,can be used.
A. an outside cutting tool B. a jet cutter
C. a string shot D. a keyseat reamer
18. Which of the following fishing tools will prevent a fish from falling downhole during a
washover? A. bumper sub
B. anchor washpipe spear C. washover pipe
D. overshot
19. When circulation cannot be established through a stuck drill sring, which of the following
- sItuations is most probably the case?
A. The drill string is stuck in a keyseat.
B. The drill string is stuck differentially.
C. The drill string is stuck by a cave-in.
D. The drill string has washed out (has a hole in it).
20. _ _ A taper tap is the most popular fishing tool in use today. (True or False)
21. Which of the following tools would most likely be used to fish out a stuck wireline tool?
A. center spear
B. taper tap
C. drillout tool D. boot basket
22. Most washover strings have less than 500 ft of washpipe. (True or False)
23. _ _ A cable-guide assembly is used-A. to recover broken wireline.
B. to locate the top of a stuck drill collar.
C. to guide a string shot into a fish.
D. to recover stuck wireline instruments with the wireline intact.
24. A poor boy junk basket catches
junk-A. by drilling through it.
B. by coring.
C. by magnetic attraction.
D. by trapping it inside inward-bending fingers. 25. _ _ A hydrostatic junk
retriever-A. operates by reverse circulation.
B. derives its power from pressure differential. C. is used only in offshore fishing operations. D. operates by magnetic attraction.
Match the descriptions on the left with the terms on the right by placing the letters in the appropriate blanks. Use each letter only once, and only one letter per blank.
26. _ _ Pumping a slug of oil downhole to free wall-stuck pipe
27. Locates depth at which drill string is stuck
28. Nonreleasing external fishing tool; seldom
used
29. Removes debris embedded in bottom of hole
30. _ _ Makes its own threads in the top of a broken-off drill collar
31. Breaks junk into smaller pieces
32. Engages broken v.ireline
33. _ _ Engages the top of a section of stuck pipe from the outside
34. Uses pressure differential to recover loose
junk
35. Records shape of top of fish
36. _ _ Prevents drill pipe from falling downhole during a washover
37. Cleans cavings out of the bore of stuck pipe
38. _ _ Self-guiding tool used to dress top of fish
39. Increases impact while knocking a fish loose
40. Buildup of solids lining the hole
A. Center spear
B. Hydrostatic junk retriever
C. Drillout tool D. Oil spotting E. Jar accelerator
F. Anchor washpipe spear G. Overshot
H. Core-type junk basket 1. Junk shot J. Die collar K. Taper tap L. Free-point indicator M. Mud cake N. Impression block O. Piloted mill III-2-4
FIGURE 37. CHEMICAL CUTrER AND SEVERED PIPE
(COURTESY OF NL McCULLOUGH. NL INDUSTRIES, INC.)
chemical cutters is that the pipe is not flared after the cut is made. Because of the close tolerances required for chemical and jet cutters to work properly, they are more commonly used to cut tubing than drill pipe.
Freeing Pipe from a Keyseat
Pipe does not always become stuck with the bit on bottom. It can become stuck off bottom during a trip - for instance, in a keyseat. Key-seating occurs when drill pipe under tension wears a slot into the wall of a crooked hole (fig. 6). The slot is usually smaller than the main borehole, too small for drill collars to pass through. If the driller is not careful while trip-ping out, he can pull the top collar into the key-seat so tightly that no amount of weight applied will make it drop free. A tool joint also can be jammed tightly into the keyseat.
To free a fish from a keyseat, a free-point indi-cator and string shot are first run and a back-off made about ten joints above the stuck point so that the top of the fish is in the main borehole
FIGURE 38. DRILL COLLAR STUCK IN KEYSEAT
and out of the keyseat (fig. 38). The fishing string can then be made up on the top of the fish in open hole.
With an undamaged tool joint looking up, a bumper sub and a keyseat reamer may be run and made up on the fish (fig. 39). The body of the
FIGURE 39. BUMPER SUB AND KEYSEAT REAMER
~ MANDREL
FIGURE 40. BUMPER SUB BEFORE DOWNWARD BLOW
bumper sub is raised the length of the sub man-drel, then suddenly dropped to strike a downward blow (fig. 40). After the fish has been knocked free, the string is lowered and rotated so that the spiraling, tungsten carbide blades on the keyseat reamer cut clearance through the key-seat. The collar string will then be able to pass through on the trip out.
If jarring does not knock the fish out of the keyseat, a washover may he tried. However, pipe stuck off bottom and not connected to the fishing string would fall to bottom when freed from the keyseat and po~sibly be damaged or lost. To pre-vent the fish from falling, an anchor washpipe
spear can be installed inside the washover pipe
before running in the fishing string (fig. 41).
An anchor washpipe spear attaches to the top of a fish and moves up or down inside the wash-over pipe in a controlled fashion. When the fishing string is run into the hole, the spear,
TOOL JOINT BOX BODY STEM CONTROL CAGE RESTRICTION RINGS TAPERED SLIP CONE _ - - SLIPS BOTTOM SUB
FIGURE 41. ANCHOR WASHPIPE SPeAR (COliRTESY OF BOWEN
latched inside the bottom joint of washover pipe, is made up directly to the tool joint box of the fish (fig. 42). The spear allows the washover pipe
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ISiii
8
-to travel downhole around the fish as the
wash-over proceeds. However, if the fish begins to
fall, slips on the spear engage the inside of the washover pipe and prevent the fish from dropping. Increased pump pressure allows the fishing string to be raised slowly past the stationary fish to make a kelly connection or to free a rotary shoe. The freed section of a partly washed-over fish can be recovered by backing off above the stuck point and pulling the washover pipe, with spear and fish latched inside, from the hole. Upon reaching the surface, the washover pipe is set in the rotary table (fig. 43). Drill pipe is run down
DRILL PIPE -""""*~ ROTARY TABLE
/
0.: .... :::.\: WASHOVER ~< ':."::". ".the fish. Some types of spears are rotated to the right to engage the fish. To disengage, these spears must be rotated to the left.
The simplest inside fishing tool is the taper
tap, which can catch a wide range of fish
(fig. 46). The tap is lowered into the collar bore and slowly rotated to make its own threads as it engages the fish. The taper tap is nonreleasing, and it is used only when a releasing tool cannot be run. Some taps have open tips, allowing lim-ited circulation for cleaning off the top of the fish; others have small side jets that move the point of the taper tap about to help locate the top of the fish. None allows a free-point indicator to pass. Once the tap is made up in the fish, the fishing string and fish are tripped out.
The taper tap should always be run with a safety
joint and jar, because once the tap is engaged it
cannot be backed out of a stuck collar. Ifjarring
does not free the fish, the safety joint can be broken out by rotating to the left and lowering the drill string (fig. 47). The coarse threads
PIN SECTION
TOP PACKER
BOTTOM PACKER
FIGURE 47. SAFETY JOINT (COURTESY OF BOWEN TOOLS.
FIGURE 46. TAPER TAP (COURTESY OF BOWEN TOOLS. INC.) INC.)
allow the safety joint to be backed out easier than a tool joint. The box section stays in the hole with the taper tap and the fish. To reattach the fishing string, the pin can be run back into the hole and made up in the box.
Fishing for OtIshore Sheared Pipe
When a floating offshore drilling rig must abandon the well site because of rough seas and there is no time for tripping out, the subsea blow-out preventer pipe rams are closed and the drill string severed. Although this procedure tempor-arily sacrifices the part of the drill string that had hung from the rig to the seafloor, it does prevent a blowout. Later, the sheared drill pipe inside the blowout preventer must be retrieved so that drilling can be resumed. A special two-step fishing method has been devised for this purpose (fig. 48).The flared end of the sheared pipe is first milled smooth, using a releasing and circulating overshot dressed with a tungsten carbide mill extension and a long, flat-bottomed guide having a soft metal surface to prevent damage to the blowout preventer pipe rams. After milling, the assembly is removed from the blowout preventer. The over-shot is dressed with a short guide, an extension sub, and a basket grapple with mill control packer. This assembly is lowered into the blow-out preventer and engages the tool joint directly above the pipe rams. The assembly and damaged pipe are then pulled from the well.
Fishing for Wireline
Wireline tools are commonly used for logging, directional surveying, and other purposes. When a wireline breaks, the line must be removed from the hole before the equipment can be retrieved.
STEP 1 STEP 2
SHEAR (SIDE VIEW) MILL-DOWN FLARE ENGAGE & PULL
(FRONT VIEW) (FRONT VIEW)
overshot on the first stand of pipe engages the
fish. Ifthe hole has a keyseat, the cable will tend
to pull into the slot.
Once the fish is caught by the overshot, the cable hanger is again attached and the spear-head rope socket is removed (fig. 52). The two ends of the severed cable are tied with a square knot or secured together with a braided hollow
cable called a snake. With the elevator latched
around the T-bar of the cable hanger, a strain is taken to pull the cable out of the fish. The cable is pulled from the hole and reeled up, and the drill pipe and fish are pulled conventionally.
/
FIGURE 53. WEIGHT AND ROTATION BEING APPLIED TO POOR
BOY JUNK BASKET
Fishing for Junk
One of the simplest rotary fishing tools is the
poor boy junk basket, which is usually shop-made
by the fishing company (fig. 53). It is run into the
hole on the bottom of the drill string to within a few feet of bottom, then lowered over the junk
while being slowly rotated. Ifthe basket is nearly
hole size, its fingerlike catchers will gather junk
toward the center of the hole and, when w~ght
is applied, bend inward to trap the junk inside. The poor boy junk basket is most effective for a small, solid mass lying loose on bottom, such as a bit cone.
A boot basket, also called a junk sub or junk
boot, may be run just above the bit during
routine drilling to collect small pieces of junk that may damage the bit or interfere with its operation, such as bit bearings or naturally occur-ring pyrite (fig. 54). Usually, however, a boot basket is run above a mill while it is milling away a metallic object such as the top of a fish.
During drilling or milling with circulation. the mud flowing upward in the narrow spac.e between
FIGCRE 52. TOOL CAUGHT IN OVERSHOT
•
•
•
FIGURE 54. BOOT BASKET
the boot basket cup and the hole wall flows rapidly enough to carry pieces of junk with it. When it reaches the annulus above the cup, how-ever, it slows down, and the larger bits of junk drop out into the cup, to be retrieved when the bit or mill is pulled.
The core-type junk basket is used to retrieve junk such as cones that mayor may not be embed-ded in the formation (fig. 55). A mill shoe is made
FIGURE 55. CORE-TYPE JUNK BASKET (COURTESY TOOLS. INc.1
pieces (fig. 59). This tool contains a shaped charge, and it must be run on drill pipe and collars to keep the force of its explosion from blowing it uphole. The junk shot is lowered on drill pipe and collars until it is just above the junk, and all fill is circulated off the junk. When the shaped charge is fired, its downward-directed
blow breaks up the junk, which can then be
recov-ered using a standard junk fishing tool.
Occasionally, the force of the explosion embeds the fragments in the formation where they will
DRILL COLLAR ELECTRICAL GO-DEVIL-~--;-CIRCULATING SUB CIRCULATION PORT--a-,-, CAP ASSEMBLY ~ DETONATOR ! SHAPED CHARGE
1
FIGliRE 59. JUNK SHOT (COURTESY OF WELL CONTROL)
not impede a roller cone bit, making a separat retrieval run unnecessary. In this case, it is goo practice to run a boot sub above the bit to catc the small pieces of junk as they are drilled out ( the formation.
The Economics of'
Fishing
Some fishing jobs can go on for months befor
the fish is retrieved.
Mter
a certain period, ho~ever, the cost of fishing operations and los drilling time become prohibitive. Generall
once these costs reach about half the cost 0
sidetracking and redrilling, fishing should b abandoned.
One way to calculate the number of days tha should be allowed for fishing uses the followin, equation:
D = V + Cs
R + Cd
where
D = number of days to be allowed for
fishing;
V = replacement value of fish;
Cs = estimated cost of sidetracking;
R = daily cost of fishing tool rental
and services; and
Cd = daily rig operating cost.
Suppose a fish worth $150,000 is stuck in well being drilled at a cost of $5,000 per day Sidetracking would take an estimated 5 days, s' would cost $25,000 plus $20,000 for equipmen and cement, or $45,000. Fishing tool rental anl
services cost $2,500 per day. The number 0
days allowed for fishing by this method would b as follows: D = $150,000 + $45,000 $2,500 + $5,000 $195,000 $7.500 = 26 days.
34
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,FIGURE 60. SIDETRACKING IN SOFT FORMATION
The operator will consider some fishing jobs impractical from the start. For instance, drill collars accidentally cemented in or engulfed in barite are nearly impossible to recover and not
worth the cost if they are recovered. The decision
is easy to make: start sidetracking immediately. Other decisions are more difficult because the odds of eventual success may not be known.
The cost of sidetracking, however, can be
esti-mated fairly easily. It takes about 5 days to set a
cement plug on top of a fish and kick off the hole to bypass it. Knowing the rate of penetration and the length of the original hole he will have to bypass, the operator can estimate the cost of drilling new hole to reach the original total depth.
Ifthe top of the fish is in soft formation, about
100 feet of cement mixed with sand or gravel is run on top of the fish. The hardened cement will deflect a spud bit into the soft formation to start the kickoff (fig. 60). In hard formation, the cement serves as a base for a deflection tool such as a retrievable whipstock (fig. 61).
Some fishing jobs are easy; others are harder, requiring special tools and the expertise of a fishing specialist. Even then, the best tools and
procedures sometimes fail. It is vital to know
everything possible about the fish and fishing
conditions before starting the job. It is equally
important to know when to stop fishing and redrill. -_..::::.. " ,...
_
-.. . WHIPSTOCK :-
---_.----
_ _- ~.(,,:'D. 0'· n - -_ _,. -- -- -- -- _ 0 00 .---' 0 o' ~~- = " 0 0 ' -~~~~CEMENT----
' or--~~-~ :(,'., o~o . - . _ 0 o · · t - - - _ - 0° 0 -C /I °0 - - - ,,0upset v: to forge the ends of tubular products so that the
pipe wall acquires extra thickness and strength near the end. Upsetting is usually performed to provide the thickness needed to form threads so that the tubular goods can be
con-nected. n: the thickened area formed by upsetting of tubular
goods.
w
wall cake n: also called filter cake or mud cake. See mud
cake.
wall hook n: a device used in fishing for drill pipe. If the
up-per end of the lost pipe is leaning against the side of the wellbore, the wall hook centers it in the hole so that it may be
recovered with an overshot, which is run on the fishing string
and attached above the wall hook.
wall sticking n: also called differential sticking. See
dif-ferential sticking.
wall-stuck pipe n: See differential sticking.
washout n: 1. excessive wellbore enlargement caused by
sol-vent and erosional action of the drilling fluid. 2. a fluid-cut opening caused by fluid leakage.
wash over v: to release pipe that is stuck in the hole by
run-ning washover pipe. The washover pipe must have an outside diameter small enough to fit into the borehole but an inside diameter large enough to fit over the outside diameter of the stuck pipe. A rotary shoe, which cuts away the formation, mud, or whatever is sticking the pipe, is made up on the bot-tom joint of the washover pipe, and the assembly is lowered into the hole. Rotation of the assembly frees the stuck pipe. Several washovers may have to be made if the stuck part of the pipe is very long.
washover n: the operation during which stuck drill stem or
tubing is freed using washover pipe.
washover back-off connector n: a fishing tool that is made up in a length of washover pipe connected to the top of the fish once the washover is completed, and then backed off the fish, thus enabling the washed-over part of the fish to be retrieved. The tool permits washover, back-off, and pulling to be carried out in one round trip.
washover pipe n: an accessory used in fishing operations to go over the outside of tubing or drill pipe stuck in the hole because of cuttings, mud, and so forth that have collected in the annulus. The washover pipe cleans the annular space and permits recovery of the pipe. It is sometimes called washpipe.
washover string n: the assembly of tools run into the hole
during fishing to perform a washover. A typical washover string consists of a top bushing (sub) or safety joint, several joints of washover pipe, and a rotary shoe.
washpipe n: 1. a short length of surface-hardened pipe that
fits inside the swivel and serves as a conduit for drilling fluid through the swivel. 2. sometimes used to mean washover
pipe. See washover pipe.
wellbore n: a borehole; the hole drilled by the bit. A wellbore
may have casing in it or it may be open (uncased); or part of it may be cased, and part of it may be open. Also called a borehole or hole.
well site n: also called location. See location.
whipstock n: a long steel casing that uses an inclined plane to cause the bit to deflect from the original borehole at a slight angle. Whipstocks are sometimes used in controlled directional drilling, in straightening crooked boreholes, and in sidetracking to avoid unretrieved fish.
wireline 11: a small-diameter metal line used in wireline
operations; also called slick line.
_ ..• __ .. ".. ''': .:'._J_ .~ __._~;~ ,-;'. ~.. ' ..
ANSWERS TO REVIEW QUESTIONS
LESSONS IN ROTARY DRILLINGUnit III, Lesson 2: Open-Hole Fishing
1. False 21.
A
2. C 22. True 3. D 23. D 4. B 24. D 5. False 25. B 6. A 26. D 7. B 27. L 8. C 28. J 9. B 29. H 10. A 30. K 11. True 31. I 12. D 32. A 13. C 33. G 14. C 34. B 15. A 35. N 16. True 36. F 17. B 37. C 18. B 38. 0 19. C 39. E 20. False 40. MTo obtain cu1ditiorwl training materials, contact:
THE
