13_Hole_Problems_and_Fishing.pdf

SPDC STANDARD DRILLING PROCEDURES MANUAL CHAPTER 13

HOLE PROBLEMS AND FISHING Page 1 of 24

EDITION OWNER CUSTODIAN

REV 04-2007 EPG-PN-W EPG-PN-WT

CHAPTER INDEX

BULLETIN ITEM PAGE

13.1 INTRODUCTION ............................................................................................................. 2

13.2 LOST CIRCULATION ..................................................................................................... 2

13.2.1 CAUSES OF LOST CIRCULATION....................................................................... 2

13.2.2 CLASSIFICATION OF LOSSES.............................................................................. 2

13.2.3 DETECTION OF LOST CIRCULATION ZONES.................................................. 2

13.2.4. PREVENTATIVE MEASURES ............................................................................... 3

13.2.5 CURATIVE MEASURES......................................................................................... 3

13.2.6 LOST CIRCULATION PILLS.................................................................................. 5

13.2.7 SPECIAL DRILLING TECHNIQUES FOR LOSS ZONES.................................... 5

13.3 DRILLING UNSTABLE FORMATION.......................................................................... 6

13.3.1 CLAY DISPERSION................................................................................................. 6

13.3.2 SWELLING SHALES............................................................................................... 6

13.3.3 CAVING SHALES.................................................................................................... 7

13.3.4 UNCONSOLIDATED SANDS................................................................................. 8

13.4 REAMING......................................................................................................................... 8

13.5 HOLE CLEANING ........................................................................................................... 9

13.5.1 WHEN IS HOLE CLEANING REQUIRED?........................................................... 9

13.5.2 RECOMMENDED HOLE CLEANING PARAMETERS (FOR HIGH ANGLE

WELLS) 10

13.5.3 HOLE CLEANING CYCLES ................................................................................. 10

13.5.4 PUMPING SWEEPS ............................................................................................... 10

13.5.5 GENERAL RULES OF THUMB............................................................................ 11

13.5.6 HOLE CLEANING BEST PRACTICES IN HIGH ANGLE WELLS ................... 12

13.6 STUCK PIPE ................................................................................................................... 12

13.6.1 STUCK PIPE MECHANISMS................................................................................ 13

13.6.2 PREVENTION OF STUCK PIPE........................................................................... 13

13.6.3 DETECTION OF STUCK POINT .......................................................................... 15

13.6.4 FREEING STUCK PIPE ......................................................................................... 15

13.6.5 BACK-OFF PROCEDURE..................................................................................... 16

13.6.6 REPORTING ........................................................................................................... 17

13.7 FISHING AND JARRING OPERATIONS .................................................................... 17

13.7.1 GENERAL PRACTICES ........................................................................................ 17

13.7.2 USE OF FISHING TOOLS ..................................................................................... 18

13.7.3 FISHING FOR CST (SIDEWALL SAMPLE) BULLETS ..................................... 21

13.7.4 ALLOWABLE PULL ON DRILL PIPE................................................................. 21

13.8 PLUGGING BACK AND SIDETRACKING OPERATIONS....................................... 22

13.8.1 GENERAL............................................................................................................... 22

13.8.2 SETTING A BALANCED CEMENT PLUG ......................................................... 22

13.8.3 SIDETRACKING.................................................................................................... 23





13.1 INTRODUCTION

Hole problems and fishing cover numerous operations, many of which are handled on a daily basis

on the rig site. This chapter highlights those areas, which may lead to the loss of the hole unless

remedial or corrective action is taken.

Reference should also be made to chapter 11, "The ABC of Stuck Pipe" (EP91 - 1908), the Drilling

Fluids Manual, the Drilling Engineers Notebook and Training to Reduce Unscheduled Events

(TRUE) manual. Several publications have been made on Borehole stability and hole cleaning.

13.2 LOST CIRCULATION

Reference should be made to chapter 11 and the Drilling Fluids Manual (EP88-2637). Although

mud losses of about 1 bbl/ft occur during drilling of loose sands in surface holes, severe mud

losses and lost circulation do not normally occur in the Niger Delta area. Lost circulation zones

have however been encountered on the periphery of the Delta and returns have been lost

occasionally when mud weights had to be increased sharply after drilling into geopressured zones.

13.2.1 CAUSES OF LOST CIRCULATION Losses may occur in highly porous and permeable formations. The severity depends on the mud

weight, Equivalent Circulating Density (ECD) and pressure surges that may be created.

Lack of care while performing leak off/limit tests and excessive Rate Of Penetration (ROP) while

drilling surface hole can also result in heavy mud losses, as can the improper handling of kicks and

drilling into depleted reservoirs with too high an overbalance.

For proper analysis, it is important to have as much information available as possible from the time

losses were detected (e.g. ROP, mud properties, mud weights in/out, solid content, sand percent,

stand pipe pressure, etc.).

13.2.2 CLASSIFICATION OF LOSSES 1. Trip losses.

2. Minor or seepage losses (less than 20 bbls/hr).

3. Moderate to severe losses (20 - 100 bbls/hr).

4. Total loss of circulation

13.2.3 DETECTION OF LOST CIRCULATION ZONES The point of initial loss in naturally occurring loss zones is normally at the bottom of the hole.

Induced fractures however, may occur anywhere in the open hole interval, but are frequently found

immediately below the last casing shoe.

If severe losses occur while tripping, circulating or increasing mud weights, the loss zone

can be at any depth. To be able to locate the loss zone, it may be necessary to run wireline logs

such as a spinner survey, a temperature survey, or a radioactive tracer survey.

Detection of mud losses during drilling is observed by a change in tank level and reduction in mud

returns. This may be accompanied by either a sudden increase in pump pressure indicating

bridging in the hole, or by a decrease in pump pressure indicating a reduction in annulus level.





Severe and moderate losses may be encountered in depleted zones or in cavernous formations, e.g.

carbonates.

13.2.4. PREVENTATIVE MEASURES Keep the mud properties within the limits set out in the drilling programme. Solids content should

be controlled within the stated limits and surface hole drilling at a controlled rate of penetration to

avoid over loading the annulus.

Avoid excessive pipe running speed to prevent pressure surges and in the areas where losses are

severe, it may be necessary to set a casing to seal off the loss zones. When loss circulation is

expected or when normal circulation has been restored after losses:

1. Keep mud weights as low as safely possible.

2. Keep the other mud properties within the limits set out in the drilling programme. In particular,

the viscosity and gel strength should be kept as low as possible.

3. Monitor the total bottom hole circulating pressure. This is equal to the sum of the hydrostatic

head due to the mud column plus the pressure drop in the annulus.

4. Run pipe slowly to avoid pressure surges.

13.2.5 CURATIVE MEASURES The most important step when losses are experienced is to maintain control of the well. This is

achieved by keeping the hole full at all times. The cause of the losses must be determined in order

to treat it effectively. If losses are as a result of fractures and are not severe, it is sometimes

sufficient to reduce the total bottom hole circulating pressure. This is achieved by reducing the

mud weight, reducing the viscosity of the mud, and reducing the cuttings load by controlling the

penetration rate and possibly by reducing the pump rate. However, it should be noted that reducing

the pump rate might actually increase the ECD if the resultant hole cleaning is ineffective.

Treating the mud in circulation with Loss Circulation Material (LCM) e.g. 5 or 10 sacks/hour of

Mica Fine and Walnut Fine added at the hopper can sometimes cure partial losses. Spotting

concentrated LCM plugs across the zone may cure severe or total losses. If losses occur while

handling a kick, LCM material should be added (nozzles sizes permitting) to the kill mud, without

any safety margin on the mud weight. If losses occur while drilling the drain hole (objective sand)

use of acid soluble "lost circulation material" like Calcium Carbonate should be considered first.

This is to prevent impairing the formation.

Setting a barytes plug is the last resort before running out of mud materials. Care must be taken to

displace this plug below the bit so as to avoid the bit being plugged. Barytes plug formulation is

given in SIPM EP 89 1500.

If a well kicks as a result of losses, then the loss circulation has to be cured first before the kicking

formation can be controlled. This can be done with LCM pills pumped down either the drill pipe or

annulus.

Trip losses and pressure surges must be reduced by improved mud conditioning and controlled

pipe handling/avoidance of excessive pipe speed respectively. If none of the various LCM pills and





soft plugs, such as gunk, sodium silicate solution etc. are successful, drilling without returns may

be considered, but this must be discussed in detail with the office.

After experiencing lost circulation problems, the setting of casing as soon as a nonpermeable zone

is encountered, should be seriously considered.

Note: Never pull out of hole when circulation is lost and mud level in annulus cannot be seen.

In cases of severe losses, if water rather than mud come into contact with the open hole, there is a

danger of stuck pipe due to destabilisation of the formation. Do not forget to remove the suction

strainers and clean out the pump after it has been used for pumping LCM pill.

a) Curing Minor or Seepage Losses (less than 20 bbls/hr):

Small continuous mud losses when drilling permeable low pressure reservoirs may occur. When

this condition prevails the procedure set out below should be followed:

1. Slow down pump so long as good hole cleaning is maintained and reciprocate string slowly.

2. Add the plugging materials slowly and continuously to mud (e.g. + 5 lbs./bbl of

mica fine, nutplug fine, etc.). If possible, the mud weight can be reduced in stages to

the minimum weight permissible, but still maintaining at least 150 psi over-balance.

b) Curing Moderate to Severe Losses (greater than 20 bbls/hr)

Spot 50 - 100 bbls of LCM pill above the loss zone and pull back into the shoe. Keep

annulus filled up with water and record the amount of water consumed. When the well

is static, calculate the new weight required. Wait for a minimum of one hour then run

back to the top of the LCM plug and circulate to the new mud weight. After circulating

and conditioning, wash back to bottom and circulate LCM pill out. When returns are

established and the minimum over-balance is still achievable, drill ahead carefully.

Note: Whenever possible, acid soluble pill should be the first option to

consider.

c) Curing Total Loss of Circulation

With total losses, a gunk squeeze can be tried. This method utilises the swelling property of

bentonite in the presence of water:

1. Clean the cement pump and lines with diesel to remove all traces of water to prevent flash

setting.

2. Pump diesel oil spacer down the hole with the bit just above the lost zone.

3. 300 lbs/bbl bentonite mixed in diesel is then pumped down, in a 20 bbl pill.

4. Follow this gunk mixture with diesel spacer.





5. Displace gunk mixture out of the bit with mud.

6. Pump simultaneously down drill pipe and annulus and apply a squeeze pressure of 100 - 300 psi.

Whilst the bentonite is pumpable when mixed in diesel, as soon as it comes into contact with

water, it forms a highly viscous, putty like material which can plug off the formation.

Sodium silicate solution is a clear liquid which, when it comes in contact with Calcium Chloride

solution, forms a white precipitate of Calcium Silicate. It is this solid that plugs off lost circulation

zones. A cement squeeze with the slurry containing loss circulation material can be considered if

all other methods fail.

13.2.6 LOST CIRCULATION PILLS It should be noted that treatment depends on severity but the idea is to have distribution of particles

as wide as possible in order to close the various pores sizes in the loss zone.

A general formulation will be as follows:

a) For minor or seepage losses:

CHEMICALS

Brine Base Fluid

Caustic Soda to provide pH of 10

HEC (viscosifier) 2 lbs/bbl

Starch (Fluid Loss) 2 lbs/bbl

Calcium Carbonate (fine) 20 lbs/bbl

b) For a moderate to severe losses, add the following to above:

Calcium Carbonate (medium) 10 lbs/bbl

c) For very serious losses, add the following to above:

Calcium Carbonate (Coarse) 5 lbs/bbl

Note: - The concentrations of the various grades of Calcium carbonate can be

increased to achieve desired results.

- A good pH is necessary for HEC to yield properly.

- Soda Ash should not be used because the viscosity of slurries made from HEC and Soda Ash

drops rapidly.

Successes have been claimed for the sized cellulose products such as "Liquid Casing". In bad cases

of losses, these products should be tried whilst keeping in mind their high price.

13.2.7 SPECIAL DRILLING TECHNIQUES FOR LOSS ZONES In some cases, lost circulation cannot be cured and some special techniques are used for drilling

the lost zones. Drilling with air, gas or aerated mud can be used but have a limited application.

Blind or floating mud cap drilling can also be carefully considered. The mud cap balances the

formation pressure. Water is pumped down the drill pipe and mud down the annulus

simultaneously. Sufficient mud is kept in the annulus to hold any formation pressure. Because of





the absence of cuttings removal, blind or floating mud cap drilling should be limited to short

intervals.

13.3 DRILLING UNSTABLE FORMATION

The following phenomena frequently give rise to drilling, completion, and mud control problems

(refer to chapter 6 for more information):

1. Dispersion of clay and other drilled solids.

2. Swelling clay

3. Caving Shales

4. Unconsolidated sands.

13.3.1 CLAY DISPERSION When clays or Shells are drilled with water-based mud, drilled solids become dispersed in the

mud, causing an increase in mud density, viscosity and gel strengths. The main cause of clay

dispersion is the nature of the formation being drilled and the type of mud in use. High

concentrations of hydroxyl ions in the drilling fluid may also increase the rate of clay dispersion,

as will the use of dispersants such as Lignosulphonate.

Treatment:

Maintain the pH below 9.5 if possible. Use non-dispersed polymer mud without lignosulphonate

dispersant. Inhibition with salts such as KCL and encapsulation with polymers will also reduce

dispersion.

Mud density and solids content can be controlled by the efficient use of well-maintained solids

control equipment. Nevertheless, the mud will have to be continuously diluted and treated to

maintain constant mud properties. SPDC recommends whole mud dilution.

13.3.2 SWELLING SHALES Some Shale undergoes plastic deformation when drilled and squeezed into the

borehole. They cause tight hole and sometimes bit balling, which may result in a stuck

string or frequent reaming.

Treatment:

If this Shale is known to be present, the mud weight must be increased prior to drilling

into the formation to prevent the start of movement. A deviated hole requires increased

wellbore support from the mud and hence the density will need to be higher than that

for a vertical hole at same depth.

Maintaining fully inhibited mud might reduce the hole problems.

On advice from the office, a proprietary additive, such as a lubricant may be added.





Note: - That the first 8000 ft in the Niger Delta has very fresh formation

water. Therefore, any swellable clay is already in a "swollen" state.

- KCl is a very effective swelling inhibitor and will deal with this issue

as well as possible for WBMs. The addition of Sodium Silicate will assist with the mud

pressure penetration problem.

- In addition, any reduction in open hole time will reduce problems as all water based mud,

however inhibiting, will eventually water wet and de-stabilise hydratable formations.

13.3.3 CAVING SHALES Shales fail when the borehole stress on them exceeds their strength as a consequence of

drilling through. Moreover, the possibility of particular shale to "cave-in" depends on

mud pressure penetration and its chemical potential (often called osmosis).

Pieces of shale (caving) are often seen in large quantities on the shale shaker once a

failure has occurred. It should be noted that a build up of these cavings and cuttings

resulting from washouts could lead to hole pack-off around the BHA.

Treatment:

Design practice to cub shale failure due to stress of drilling - Borehole stability Template.

Of most importance is to immediately increase the mud gradient to an adequate level to

stop or at least minimise the amount of cavings. Slow incremental increases in mud

gradient are not advised since significant failure of the borehole will occur if the mud

gradient is too low. It is always advisable to increase the mud gradient prior to entering

known weak shale.

Waiting for cavings to appear over the shale shakers before increasing the mud gradient

should only be done when shale encountering was not anticipated.

Good hole cleaning is critical to minimise the risk of stuck pipe in caving boreholes. The

following factors play important roles in keeping the hole clean:

1. Mud viscosity with YP ranging between 40 to 50 lb/100ft2

2. Pipe rotation

3. Maximum circulation rates

In addition,

- mud pressure penetration can be greatly reduced by use of Sodium Silicate or

eliminated with POBM/LTOBM

- Minimise nozzle velocity when drilling unstable formations by using larger

nozzles, a rule of thumb is to keep it less than 300 ft/sec. (it is desirable to run

bits without nozzles when wiper tripping to ensure high annular velocities).

The rheology should be adequate to clean the large diameter cavings, with their high slip





velocity, out of the hole.

13.3.4 UNCONSOLIDATED SANDS Enlargement in unconsolidated sands is a common phenomenon in the Niger Delta,

from surface to + 8000 ft. This gives rise to difficulties in log interpretation, formation

testing and completion. When drilling productive unconsolidated sands, care must be

taken to minimise washouts and avoid bad primary cementations.

13.4 REAMING

Whenever an under-gauged bit is pulled out, at least the last 60 feet has to be reamed before

drilling ahead with the next bit.

Whenever a mud motor is run for kicking off or course correction purposes, the mud motor drilled

section must be reamed and "smoothed out" before drilling ahead, to prevent likely hole problems.

When reaming is necessary, use the following guidelines:

1. With a jet bit, reaming is to be done using 50 - 70% of the previous pumping rate used

for drilling. Do not ream with the same pumping rate as used for drilling as it may

create a 'mud ball' ahead of the bit, resulting in a hydraulic piston which can break

down the formation. Care should be taken to prevent drilling a new hole in a directional

well. (Compare MWD data with plotted hole direction).

2. When excessive reaming is anticipated, a conventional rock bit with extra gauge

protection should be run without nozzles and the normal drilling circulation rate used, as

cuttings/cavings must still be removed from the hole.

3. Extreme care should be taken when reaming bridges, as percolated gas may have

accumulated below the bridge.

4. When heavy reaming is encountered, the string should be picked up at frequent intervals

and lowered to check if it is possible to wash the string past the tight spot, without

rotating.

5. When reaming a mud motor section, do not use a stiff assembly, as there is a danger of

side tracking the hole. Use a semi stiff assembly e.g.:

Bit, NB Stab, 2 x DC, Stab, 2 x DCs, Stab, etc.

6. With excessive reaming, the solids build-up in the mud may cause problems. Ensure

the hole is effectively cleaned and the solids control equipment is operating efficiently.





13.5 HOLE CLEANING

One of the major problems in SPDCs drilling operations is stuck pipe due to "Hole Pack-Off" (due

to solids). This is common in highly deviated and horizontal holes with inclination greater than 350.

Whilst some actions can be taken to reduce the occurrence of unstable hole, particularly by using

sufficient mud density to delay the onset of borehole collapse, the problem can be alleviated by

keeping the hole as clean as possible.

Boreholes become more difficult to clean as the angle increases. At high angles, cuttings beds tend

to slide down the low side of the hole and may accumulate, causing the hole to pack-off.

Appropriate hole cleaning approach must therefore adopted depending in well bore inclination

a) 0° to ±35° wells: Mud rheology & flow rate are designed to keep cuttings in suspension and

combat slip-velocity.

b) ±35° to ±60° wells: Hole cleaning practices are designed to combat cuttings avalanching.

c) >±60° degree wells: Hole cleaning practices should be designed to move cuttings in a long,

stationary bed (with a short avalanche interval in the build section)

Note that a high angle wells must deal with each of these intervals.

Mud rheology (viscosity) has a great effect on the hole cleaning in vertical wells, where it may be

said that in general, the higher the viscosity, the better the hole cleaning will be. However, once

cuttings have fallen to the low side and cutting beds formed, then low viscosity fluid pumped at

high annular velocity combined with rotation of drill string at very high speeds will have effect.

This is because the flow approaches turbulence and stirs up the cutting beds with a scouring action.

13.5.1 WHEN IS HOLE CLEANING REQUIRED?

In general hole cleaning cycles are mandatory at any of the following stages:

� Prior to any trip out of the hole!

� For remedial hole cleaning when a hole cleaning problem is evident (e.g. diverging T&D,

excessive ECD, limited cuttings returns).

� Prior to drilling into a known or suspected loss circulation zone.

� Prior to any back-reaming on trip out.

� During back-reaming if signs of packing off are seen.

Cleanup cycles are not a waste of time “Sometimes you have to go slow to go fast”





13.5.2 RECOMMENDED HOLE CLEANING PARAMETERS (FOR HIGH ANGLE WELLS)

In all cases keep close watch over string vibration, ECD and torque

13.5.3 HOLE CLEANING CYCLES

Generally a minimum 2 or 3 x cleaning cycles or bottoms up (sometimes up to 4 to 6) is required

to cleanup a high angle hole. The number of BU will increase with:

� Increased measured depth

� Higher inclination

� Larger hole size

� Reduced parameters (rpm, flowrate, viscosity)

NOTE: The absence of cuttings over the shakers does not mean that the hole is clean. Experience

has shown that cuttings usually come in two or more waves over the shakers

13.5.4 PUMPING SWEEPS

� When sweeps are pumped, carefully document to avoid doing the same thing twice and

expecting a different result. � Pipe should be rotated continuously at 120+rpm in hole sizes >9⅞”.

� Do not stop pumping till the sweep is completely out of hole.

� Consider alternative sweep types such as Tandem lo-vis / hi-vis sweeps and weighted sweeps.

60 350 - 400 70 – 100 450 - 600 8½”

100 500 120 – 150 700 – 900 9 7/8”

120 650 - 700 150 – 180 800 – 1100 12¼”

120 800 120 – 170 850 – 1150 14½”

120 800 120 – 150 900 – 1200 17½”

Drillstring

rpm

Flowrate (gpm) Drillstring

rpm

Flowrate (gpm) Hole Size

Minimun for Effective Hole

Cleaning

Desirable for Good

Hole Cleaning





13.5.5 GENERAL RULES OF THUMB 1. A minimum flow-rate must be maintained when drilling, washing and reaming down and

pumping out, sufficient to clean the hole. The required annular velocity to clean a 50- degree angle

hole is double that required cleaning a vertical hole.

2. Minimise nozzle velocities to less than 300 ft/sec. when drilling soft or unstable formations.

3. Use cuttings bottoms up for circulating clean. This may be up to twice as long as gas bottoms

up, in deviated or washed out holes.

4. If losses are encountered, in general, the pump rate should not be reduced, as inadequate hole

cleaning will increase the chance of the hole packing off. Also, the increased annular cuttings

loading will often increase the ECD and exacerbate the losses.

5. During fast drilling, if the hole is not cleaned, as evidenced by increasing torque and drag or

insufficient cuttings on the shakers, time should be taken circulate the hole clean and the section

"controlled" drilled (if directional constraints allow). This will reduce the cuttings volume and

spread them evenly throughout the annulus, minimising the chance of packing off.

Sweeps should fill 300 feet of the annulus if possible. Check the effect of weighted/unweighted

sweeps on the hydrostatic pressure.

Note: Low viscosity sweeps are especially effective in deviated holes by stirring up the cutting

beds and in removing smaller cuttings from washouts. Viscous/high density sweeps are most

effective in vertical and low angle holes and in removing larger or heavier cuttings and

cavings.

6. The volume and physical appearance of the cuttings arriving at the shakers should be

closely monitored to assess hole-cleaning efficiency. If in doubt, pump a low/high

viscosity sweep and check returns.

7. If the shaker capacity is overloaded and surface losses are occurring, drilling must be interrupted

whilst the screens are changed. If this is ineffective, the ROP must be restricted. On no account

must the flow-rate be reduced.

8. In high angle wells (>45 deg.) high rotary speed, up to 180 RPM if possible, is effective in

"stirring up" cutting beds and improving hole cleaning. Therefore, the string should be pulled off

bottom and reciprocated whilst rotating as fast as possible for five to ten minutes whilst circulating

prior to a trip.

9. If directional constraints allow, the procedure in item 9 should be followed after

oriented drilling (sliding) with a downhole motor. It is vitally important to rotate the

string to move the cutting beds, particularly whilst pumping any mud sweeps.





10. Mud sweeps should be used as a check on hole cleaning, to see if the annular velocity

is sufficient and the mud rheology is suitable, it should never be necessary to pump

sweeps in order to be able to continue drilling.

13.5.6 HOLE CLEANING BEST PRACTICES IN HIGH ANGLE WELLS

BEST PRACTICE REMARKS

1 Use of adequate pump rates at all time Minimum flow rates for different hole sizes

as recommended in section 13.5.2 is

mandatory

2 Use maximum practical RPM, raise the drill

string slowly (5 min/std) and slack-off at a

safe but fast rate (1 min/std)

Minimum drill string rotary speed for

different hole sizes as recommended in

section 13.5.2 is mandatory

3 Select optimum rheology and maintain mud

properties in optimum range

4 Consider pumping high-vis sweeps in wells

at low deviation (<35o). Consider

low-vis / high-vis sweeps in wells at higher

deviation (>35o)

Must be done with the minimum

recommended rpm and mud flow rate.

BEST PRACTICE REMARKS

1 Plan the well with minimum possible build

rate and during drilling minimize DLS to <

4o / ft

This should be done/attempted on a best

endeavours basis

2 Plan a reaming/wiping trip if hole geometry

exhibits high DLS

Mandatory for intervals drilled in the

sliding mode. Trip may be done with a

different BHA.

3 Short trip frequently every 500ft to 700ft

depending on hole quality

Very necessary for real time hole cleaning

4 Before connections, wipe the hole at full

circulating (5 - 10 min), rotating at

maximum RPM when possible

Very important to clean the hole while the

cuttings are being generated. Usually more

difficult after cuttings bed has formed

5 Back reaming For hole cleaning purposes, use

backreaming only as a last resort.

Be aware: Use of sleek BHAs can mask the presence of cuttings bed on the trip out.

13.6 STUCK PIPE

Pipe sticking is an expensive, time consuming problem, which can lead to loss of equipment, side

tracking and some times complete loss of hole. It is defined as the inability to raise, lower or rotate

the drill string due to one, or a combination of causes. Further information can be found in the

Drilling Engineers Notebook, "ABC of Stuck Pipe" (EP93 – 1908 and EP94-1908)





13.6.1 STUCK PIPE MECHANISMS a) Differential Sticking

This is a sticking force which develops when the mud's differential pressure (overbalance) forces

stationary Bottom Hole Assembly (BHA) onto the thick filter cake across a permeable zone. It

should be noted that the pipe needs only to be stationary, for a very brief period such as a

connection change for it to get stuck.

Therefore, mud properties, particularly mud density, but also fluid loss, filter cake thickness and

mud solids play a significant part in differential sticking. BHA configuration is also of key

importance, i.e. length, OD and stabilisation.

Thickness of the filter cake will affect the sticking force, the thicker the cake, the greater the

contact with the pipe. Also, the contact area and hence the sticking force will increase with time.

When differentially stuck, circulation remains unaffected but pipe movement is not possible in

either direction.

b) Mechanical Sticking/Hole Geometry

This category of stuck pipe occurs when the hole diameter and/or angle relative to BHA geometry

and/or stiffness will not allow passage of the drill string. Possible causes are under-gauge hole, key

seating, and stiffness of the BHA, ledges, micro doglegs and mobile formation. In general, it

covers all the causes related to hole configuration and not those related to hole cleaning.

The common aspects of these causes is that once the string is stuck, circulation is not affected, the

problem occurs when moving the string and it is often "one way" either coming up or going down.

c) Solids/Hole Pack-off

This category encompasses stuck pipe caused by cuttings, cavings, hole collapse, reactive

formation, fractured and faulted formations, etc. It has to do with hole cleaning and hole stability,

which are often related subjects and affected by mud properties (mud density, inhibition,

rheology). Hole cleaning is difficult in a washed out hole and continuous generation of cavings

makes efficient hole cleaning very difficult. The common observations for the stuck pipe causes in

this category are that circulation is often restricted, the problem is "one way" and in most cases

occurs when pulling out.

13.6.2 PREVENTION OF STUCK PIPE a) Mud Properties

1. Maintain mud properties within the programmed specifications, time spent circulating at the

shoe to condition the mud could prevent loss of the hole.

2. Increase mud inhibition or encapsulating chemical concentrations if the cuttings become sticky

or show a tendency to break up and disperse.





3. If shakers become overloaded, reduce the ROP to allow the mud to clean the hole. "Bottoms up"

time is greatly increased with hole deviation due to the cuttings settling on the low side of the hole

- allow for this when circulating clean.

4. When the mud density has to be increased to control unstable Shales in known problem areas,

ensure that it is carried out before entering the problem zone (i.e.) be proactive, not reactive. After

increasing mud density, do not decrease it, as this will contribute to borehole instability.

5. Should the hole conditions dictate that an increase in mud density is required, do it without

delay.

6. As a rule of thumb, it takes an increase of 0.026 psi/ft. (0.5 lbs./gal.) mud density to stabilise the

hole for each 30 deg. increase in hole angle.

b) Procedures:

1. Maintain good hydraulics when drilling, avoid excessive jet velocities as these will contribute to

washed out hole, but use high enough annular velocities to clean the hole.

2. Never keep the pipe stationary in open hole, particularly in depleted sands, or areas of known

differential sticking problems, consider rotating the string during a connection change.

3. Minimise the BHA, include a jar and use spiral DCs (the minimum required). Consider using

HWDP or smaller diameter DCs. Not more than 90 ft of DCs in 12-1/4" hole section should be run

unstabilised. Use melon shaped stabilisers whenever possible and always gauge the bit and

stabilisers when out of the hole.

4. Monitor torque, drag and carry out wiper trips if necessary.

5. Prior to tripping, circulate the hole clean of cuttings and cavings and when tripping, the DS must

be on the rig floor for at least the first 10 stands pulled, whenever tight spots are encountered and

for the last 10 stands in.

6. When tripping, do not pull more than half the DC weight below the jars. When working the

pipe, the overpull should be increased in 10 kips increments and always keep going back to where

the string was free. Use the top drive, or install the kelly at any stage.

7. If pumping out is necessary, circulate at intervals to prevent the hole packing off.

8. Always wash/ream the last two joints to bottom.

9. Ensure shift Drillers leave detailed handovers at the end of each tour, highlighting any hole

problems, which may help the next Driller during a trip.





11. Plan ahead, in highly deviated wells, consider including a drilling accelerator in the string, in

remote locations keep the back-off equipment on site. The recipe for a spotting pill should be

known and the required chemicals on site.

13.6.3 DETECTION OF STUCK POINT Detection of the stuck point is necessary in order to find the deepest possible place for a back off.

An approximate depth can be determined using the stretch method, for a more accurate depth of

the stuck point, use the wireline Free Point indicators.

a) Stretch Method

The stuck pipe is stretched and marked accurately at surface. Using the formula, an approximate

depth of the stuck point can be obtained. However, hole deviation will result in less reliable values

due to hole friction.

L = 735294 x Wdp x e

P

Where:

e = Elongation in inches

L = Length of free pipe in feet

P = Load, pull in lbs

Wdp = Plain end pipe weight in lbs/ft

b) Free Point Indicator Tool (FPI)

The FPI is run on electric wireline inside the pipe. This is a more accurate method than the stretch

method. By applying stretch and torque on the pipe, the FPI run in tandem with a CCL can be used

to accurately determine the free point and the deepest tool joint for back off.

13.6.4 FREEING STUCK PIPE The first actions taken when the string becomes stuck have the greatest chance of success. Ensure

that contract personnel are aware of the correct procedures. Analyse the type of sticking

mechanism, as a correct interpretation will greatly increase the chances of success.

1. If the string was moving immediately prior to being stuck, move in the opposite direction, as

soon as possible, using the jars if necessary.

2. Work the pipe to its limit immediately, know the maximum load that can be pulled.

3. If differential sticking is suspected, work right hand torque into the string and slack off. If

unsuccessful, pull to the maximum and commence jarring.

4. Immediately the string becomes stuck, mix and pump a spotting pill. It should be the same as

density as the mud and the volume should be sufficient to cover the BHA with enough excess to

pump one bbl every half-hour for a 12-hour period. Even if the string is not differentially stuck, the





spotting pill may prevent the string from becoming differentially stuck, plan to soak the string for

12 - 24 hours.

5. Mud acid pills may also be considered. It is mixed using HCl and inhibitors and works by

dissolving the filter cake and the formation. All safety precautions must be taken when mixing a

mud acid pill. It also has a detrimental effect on the mud and considerable mud conditioning will

be required.

6. If differentially stuck, consideration should be given to reducing bottom hole hydrostatic

pressure. This should only be carried out after discussions with the base SDE. All precautions to

control the well in the event of kick must be in place and the personnel warned in advance.

13.6.5 BACK-OFF PROCEDURE The back-off operation (with strands of primer cord) consists of transmitting left-hand torque to

the joint to be broken, while applying pull for neutral weight at the back off depth. An explosive

device is positioned by a CCL on electric wireline in the joint to be broken. The primer cord is

detonated in the tool joint and the combined effect of the explosion and left torque unscrews the

connection.

a) Safety Precautions for String Back-off

1. Tong and slip dies must be clean, sharp and of the correct size. Tongs and back-up lines must be

in good condition (double back-up lines are often used).

2. Since there is a possibility that the string might part higher-up, tie the slip handles together to

keep the slips around the pipe.

3. When torque is applied, the elevator should be latched around the pipe but should be free from

the tool joint to enable free rotation. Where the kelly is in use, make sure that the hook is unlocked

when the pipe is being rotated.

4. When the string is picked up, ensure there is no residual torque remaining in the string.

5. When the string shot charge is run in the hole, ensure that only "one" of the table locks is

engaged to make it possible to release the table after torquing up and firing the shot.

6. When the string shot has been fired and no positive indications of back-off is observed, treat the

rotary table with great care. Strings have been known to come free half an hour or more after firing

the string shot.

7. When coming out of hole with the backed-off pipe, check all connections for correct make-up

torque.

b) Working Left-hand Torque down the Hole

It is necessary to work left-hand torque down the hole to the desired back-off depth, especially in

crooked or deviated holes.





In order to work the torque down, the Kelly must be installed with the bushing in the rotary table.

If the drill string become stick whilst round-tripping or making a connection, hang the string off on

the pipe rams, remove the top single and install the kelly.

Working torque down the hole using rig tongs is ineffective and dangerous. Always try to use the

kelly. Where the kelly cannot be installed, slips and elevator can be used with great care.

The tool joint to be backed-off should have a zero load, however in practice, this is difficult to

achieve and it is better to have the joint in slight tension rather than compression.

Calculating the surface pull to achieve this force at the proposed back-off point is generally done

assuming no buoyancy effect since the pipe is held down. However, as soon as the joint is cracked,

the buoyancy effect will act on the freed string. The calculation of required pull is outlined in the

Drilling Engineering Notebook, section G.

If after several attempts a back off cannot be achieved, consideration should be given to running

the Schlumberger Colliding tool or a similar device.

13.6.6 REPORTING The "STUCK PIPE REPORT", the "FISHING REPORT" and the "EVENT

ASSESSMENT REPORT" must be completed after these incidents. Ensure they are completed

accurately and in full and submitted to the SDE, Well Equipment Specialist and the Performance

management Co-ordinator in order that the data can be utilised to prevent further incidence of

stuck pipe.

13.7 FISHING AND JARRING OPERATIONS

All fishing operations are classified as lost time and as such should be dealt with as quickly as

possible. However, all efforts must be made to ensure losing the fishing string does not compound

the fishing problem.

Always have a range of overshot bodies and grapples for fishing all tubular sizes in regular use.

When non-routine operations involve different sized tubular, endeavour to have the correct fishing

equipment on site.

13.7.1 GENERAL PRACTICES The standard fishing assembly is as follows:

1. Overshot, Fishing jar (18 inches stroke), Hydraulic jar, DCs, DP, Kelly. Use mechanical jar only

if hydraulic jar is not available.

2. To get the maximum jarring effect, the same amount of DCs as left in hole should be run on top

of the jars. A jar accelerator can also be run on top of the drill collars, this is especially

recommended in deviated holes or when fishing at shallow depth.





3. Do not run a safety joint with a fishing assembly because experience has proved that jarring on a

safety joint freezes it and makes it useless. Also, it will not be possible to use a string shot for back

off, as left-hand torque cannot be applied to the string.

4. Always use a basket grapple in preference to a spiral grapple, whenever possible, especially

when fishing tubing or thin walled pipe.

5. When a twist off occurs, circulate the hole clean and spot a viscous pill before pulling out of

hole. Avoid washing out the hole just above the top of fish as this could cause difficulty in latching

onto the fish.

6. When fishing stuck tubing, wherever possible, fish on collars or connections as less deformation

to the top of the fish occurs. Wireline re-entry could be required at a later stage and this may be

difficult if the tubing is deformed.

7. Prior to pulling out any fish, particularly packers, circulate bottoms up to ensure no gas is

trapped below the fish. When heavy jarring has been done, all connections must be checked for

correct make up torque.

8. When pulling a fish, the pipe should not be rotated out and any working of the string should not

be above the maximum yield of the pipe. When jarring with a jar close to surface, torque up the

string to the right from time to time, to avoid premature back-off.

9. When jarring, do not exceed the impact force recommended by the manufacturers. The

following formula will give the theoretical impact:

0.000374 x Weight of DCs above Jar x Overpull = Impact Force in lbs.

10. Refer to the Drilling Engineers Notebook for additional information on the correct fishing tools

to have on site depending upon the hole size being drilled.

13.7.2 USE OF FISHING TOOLS

a) Drilling Jar

1. The drilling jar should never be positioned below tools with a greater diameter than that of the

jar. This is to reduce incidence of the bigger OD tools above the jar getting stuck and rendering the

jar useless. As a rule of thumb, a jar should be placed at the top of the drill collars with one drill

collar above it.

2. For rigs that use Kelly, heavy pulling and jarring must be done with the Kelly added to

the string. Where this is not possible, the elevator latch should be secured with rope or

chain.

3. Never use an 18 degree shoulder elevator for jarring, always use a square shoulder and





the correct elevator.

4. Regularly check the derrick and lifting equipment for loose bolts, etc. Slip block line

after every 2 - 4 hours of jarring.

5. Whenever possible, the jar should be in tension during drilling unless using a type of jar

recommended to be run in compression. Never run a jar in the neutral point, and

always follow manufacturer's operating procedures.

6. When the drilling jar connection has to be broken, two tongs should be used if the jar is in a

cocked position. This is because the momentum of the drill collars below the jar can create enough

left-hand torque in the jar to cause it to trip. This could cause the slips to jump loose in the rotary.

Use a safety clamp around the jar to prevent the jar from tripping in the derrick.

7. Jars should always be run at least 30 feet above any reamer/stabiliser to allow the jar to

flex. Never run jars immediately below a crossover.

8. The pull to trip a jar = original weight indicator reading + the jar trip setting (this is an

acceptable rule of thumb).

9. If the hole drag is close to the tripping weight of the jar, care should be taken and a

"wait period" must be exercised prior to releasing the elevator for changing a

connection. (String has been known to jump out of the slips). This is valid for running

in and pulling out.

b) Overshot

1. The overshot is the most common fishing tool to externally engage, pack off and pull a

fish. It is very simple to engage and disengage from the fish when desired.

2. The Bowen overshot commonly in use in SPDC requires right hand rotation for

engaging and releasing.

3. Prior to running an overshot, a detailed drawing including all external and internal

dimensions must be made of the complete fishing assembly.

4. When Top Of Fish (TOF) is located, either by weight decrease or pressure increase,

the overshot must then be run over the fish to about ½ ft above top of grapple. This

will avoid "butting out" of the fish in the overshot and ensure that there is sufficient room

inside the overshot to come off by beating down.

5. When there are hydrocarbons below TOF, no pack-off element must be used in order

to allow for circulating bottoms up prior to POH. Note that strings could be plugged

with cuttings after a drill string failure while drilling.

6. Do not use an overshot with a much larger OD than required. This is to enable fishing





the overshot itself if it parts in the process (e.g. 5-3/4" overshot can be fished with a 7-

7/8"). On the other hand, overshot with a small OD could go past TOF unless an

oversize guide shoe is run.

7. If an overshot is to be used for mechanical back-off, strapping of the overshot bowls

may be necessary to avoid backing off on the fine threads of the overshot.

8. Before locating the fish with an overshot, the string weight up and down must be

established.

9. If any form of wireline work (e.g. string shot for back off or severing of pipe) is

envisaged, ensure that the complete fishing string is drifted with the appropriate drift.

c) Jar Intensifier or Accelerator

The function of the intensifier is to supply acceleration to the upper end of the jar during

jarring. This gives an upward blow of higher impact than can be obtained with only the

jar. It should be placed in the HWDP section of the string.

The accelerator is valuable in deep and crooked holes where much of the stretch of the

string is lost in friction, or at shallow depths.

d) Junk Sub/Jet Junk Retriever

A junk sub can be used to recover junk such as lost cone inserts. The small junk is

jetted from the bottom of the hole and rises sufficiently before falling into the junk

basket. When using a jet junk retriever for recovering junk, it is

important to core approximately 6 inches and then pick up string to allow junk on the

side of the wall/basket to fall into the pilot hole. This ensures that it can be recovered

when coring is continued. Maximum length of core depends on the size of the basket

but it is usually 1-1/2 to 2 feet.

e) Spears

The spear offers an easy means of engaging a fish internally. The standard assembly for

a spear is as follows:

Spear, Fishing jar (3 foot stroke), DCs, DP, Kelly (for rigs without TDS).

Engagement of the fish is done by turning the string a quarter to the left, (this disengages

the slips), followed up by picking up to engage fish internally. To release from the fish

when desired, knock down on the slips by applying a quick slack-off, followed by

rotating to the right and picking up.

Before running a spear, ensure that all dimensions are known and string weight up and

down should be checked as well as the circulating pressure, before engaging the fish.

When releasing a spear, if knocking down does not free it, then install a surface jar (4-ft

stroke) and jar down. The 4 ft surface jar and 3 ft downhole jars are chosen, as this





combination enable the down hole jar to close completely before the surface jar.

The Bowen ITCO spear can be run with a stop ring, this spear is easily released by torque.

13.7.3 FISHING FOR CST (SIDEWALL SAMPLE) BULLETS If bullets from a CST gun are lost in hole, run in with a conventional hard formation

rock bit, with not less than 3 x 18 nozzles and a junk sub. Rotate and circulate several

times along the hole sections where the bullets were lost to attempt to dislodge the

bullets from the wall of the hole.

When on bottom, fish for junk, drill a few feet. If no significant torque is encountered,

continue as per programme. Do not continue drilling with junk sub, as this constitutes

the weakest point in hole.

If drilling indicates that there is junk on bottom which cannot be broken and recovered

in the junk sub, pull out and run a reverse circulating junk basket to fish for the junk.

13.7.4 ALLOWABLE PULL ON DRILL PIPE When determining the pull on stuck pipe, the actual weight of the string in air is to be

used and not the buoyant or weight-indicator weight.

Where pipe is stuck and jarring or a straight pull is necessary, the following values, and

recommendation based on API RP7G, Drill Stem Design and Operating Limits, should

be followed:

a) Classification of Grade

For Tension

Premium pipes 2 - 20% uniform wear.

For Torsion

New : Direct from factory

Premium : DP having uniform wear (max. 20%) and minimum wall thickness of 80%.

Section C in the Drilling Engineers Notebook gives values for the maximum tensile load on new,

premium and grade 2 drill pipe. They are based on minimum yield values and do not include any

safety factors. It is advisable not to pull more than 80% of the quoted values.

Whenever loads are pulled close to maximum, ensure that the rig floor is clear of unnecessary

personnel. Whenever maximum loads are pulled on the drill string and a drilling jar is included on

the BHA, it is always necessary to trip the jar prior to pulling to desired maximum pull. Failure to

trip the jar before pulling may result in additional dynamic loading which could exceed the elastic

load limit, putting the pipe into plastic loading and causing permanent deformation.





13.8 PLUGGING BACK AND SIDETRACKING OPERATIONS

13.8.1 GENERAL If a bottom hole assembly or logging tool cannot be recovered economically, there is

little alternative other than to plug back a section of the hole above the fish and then

sidetrack the fish.

A hole is plugged back usually by setting a cement plug. Note that the top of cement

must be confirmed with a bit. If the section is to be plugged back into the casing and it

is planned to reduce the mud hydrostatic pressure to less than that of the highest

formation pressure drilled, the integrity of the plug must be confirmed with a pressure

test and an inflow test.

To prevent cement slurry dehydration and consequent flash setting when plugging back

over very permeable sand, fluid loss control additive is used in the cement slurry to give

a water loss of less than 50 mls. The cement formulation should be such that a hard

plug results, often by using dense slurry [e.g. 0.88 psi/ft (2.04 SG)]

If a calliper log is available, use it to calculate the required volume. If exact volumes are

known, use theoretical volume for balanced displacement.

If the hole is badly washed out, it is better to set two short plugs over the washed out

interval than to try to cover the complete interval with a large amount of cement, which

may result in heavy backflow or a poor quality cement plug.

It is common in SPDC to set cement plug using 2-7/8" or 3-1/2" tubing stingers.

Always ensure there is about 600 ft of such tubing on site.

When mud is highly treated with lignosulphonate, (which acts as retarder) ensure good

scavenging and separation ahead of the cement slurry and allow for uncertain setting

time. Use a water-spacer ahead and behind the cement slurry and avoid stabbing the

stinger back into the cement plug when displacement is completed.

13.8.2 SETTING A BALANCED CEMENT PLUG 1. Run a tubing stinger on drill pipe to the desired depth of the bottom of the plug to be

set. The length of the stinger should be equal or greater than the height of expected

column of cement.

2. For good placement of a balanced cement plug, use a balanced water spacer column

ahead and behind the column of cement. The "equalisation point" formula is:

N

h = --------------

C + T





Where:

N = Volume of cement slurry used (in barrels)

h = Height of balanced cement column (in feet)

C = Barrels per linear foot of space between tubing and casing (or hole) (i.e. annular capacity

between stinger and hole in bbls/ft).

T = Barrels per linear foot inside tubing (i.e. capacity of pipe or stinger in bbls/ft).

3. When height of cement column in the string plus the height of water spacer behind is

subtracted from the string length, the displacement volume can then be accurately

known. For small plugs and accurate placement of small volumes, use the cement

pump for displacement.

4. Pump the calculated water ahead for effective scavenging, mix and pump the desired

cement volume, then pump the water behind to balance the column of water ahead.

Note: Use dense "neat" cement with tight fluid loss control (in open hole) in

order that a firm, hard plug be obtained to give a definite kick-off.

5. Chase with mud (or brine) until the cement, water and mud columns in pipe and annulus

balance. (To prevent 'wet' tripping, the cement may be under-displaced by the

displacement volume of the stinger).

6. Pull back until the pipe is at least 1,000 ft above top of cement and circulate out excess

cement.

13.8.3 SIDETRACKING Sidetracking is a way of diverting the course of a well from a fish or a wrong course, to

a required target, relief-well or any zone of interest. A kick off is most successfully

carried out using a mud motor and a MWD.

Prior to running the KO assembly, the cement plug should be weight tested to 30 kips

and dressed to the desired kick-off depth with a bit.





CHAPTER 13: Hole Problem and Fishing FEEDBACK FORM

Use this form to communicate:

1. Any inaccuracies or confusion in the text

2. Ease of finding information

3. Adequacy of reference

4. Too many or too little detail

5. What is missing?

6. What is not required?

7. Any other suggestions or comments

NAME: DEPT.: TELEPHONE: Please dispatch form to EPG-PN-WTE (Technical Standards)

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