w- 1

Primary recovery depends upon natural reservoir energy to drive the oil

through a complex pore network to producing wells. With the passage of

time, the producing wells for various reasons become sick and a steep fall in

their production levels is registered. To repair these sick wells and rejuvenate

oil production from them, work over operations are carried out.

The primary objective of workover operation is to maintain the wells in

optimum producing condition.

The rig which is smaller for doing this job is called �WORKOVER RIG�.

This rig is smaller than the drilling rig as far as capacity, height, leg spacings

etc are concerned.

In addition to solving specific well and reservoir control problems,

workovers can provide a check on lateral and vertical movement & current

location of oil, water & gas in specific zones & reservoirs.

Surface Equipments of a standard workover Rig

1. Rotary Table. 2. Prime movers. 3. Derrick 4. Substructure. 5. Drawworks

6. Mud Pumps. 7. Blow out preventers

1. ROTARY TABLE: - The rotary table has two primary functions.

a) It transmits the rotation to the drill string by turning the Kelly joint.

b) It suspends the pipe weight during connections & trips

Normally, the table is chain-driven through the draw works, although a

smaller separate engine is sometimes used as an independent unit.

2. PRIME MOVERS: - Currently I.C engines are the most common.

id5367218 pdfMachine by Broadgun Software - a great PDF writer! - a great PDF creator! - http://www.pdfmachine.com http://www.broadgun.com

w- 2

3. DERRICK:- The derrick is the structure which affords the vertical

clearance necessary for conducting such operations as running in &

pulling out of tools and tubings. It must be strong enough to withstand the

loads imposed upon it.

These loads vary with depth and the size of hole and casing.

An attempt to reduce operating costs now-a-days, portable unitized rigs are

being used. The entire rig is mounted either on skid or trailer for maximum

portability.

The principal advantages are savings in transportation costs & rig up.

4. SUB-STRUCTURE:- The substructure, as the name implies, is the

support on which the derrick rests. This must be of sufficient strength to

support the anticipated loads with adequate safety factor. Its height must

be sufficient to house & afford access to the blow out preventors.

5. DRAW-WORKS: The draw works or hoist is the key piece of

equipment. Its functions are:

a) It is the control centre from which the driller operates the rig. It

contains the clutches, chains, sprockets & other controls which enable

the rig power to be diverted to the particular operation at hand.

b) It houses the drum which spools the drilling line during hoisting

operations and also feed-off, during running-in. Draw-works are

commonly designated by a horse-power and depth rating.

6. MUD PUMPS: The function of the mud or slush pump is to circulate the

drilling fluid at the desired pressure and volume. The pump normally

used for this service is the reciprocating pump, double acting, duplex

type. Pumps are commonly rated by hydraulic horse power.

w- 3

7. BLOW OUT PREVENTERS : it is not always possible to predict the

exact magnitude of pressures which will be encountered while doing a

job in the well consequently, it is not uncommon to encounter pressure

greater than those imposed by the drilling fluid , with the result that

formation fluids flow into the borehole and eventually to the surface. This

effect is called a blow-out and this can be checked by means of blowout

preventor. Its function is to close the annulus between two concentric

pipes.

Most of them are hydraulically or pneumatically operated, manual operation

available as a safety precaution. The pressure rating of blow out preventers is

dictated by the hazards of the area and depth in which they are used.

DRILLING LINE: It is the wire rope which is spooled on the drum of the

draw work hoist, reeved on the crown block and traveling block and used in

hoisting tubings in making a trip.

SAND LINE : The sandline is spooled on the sand reel, passed over a

sheave at the top of the derrick and is normally attached to a bailer which

stands vertically to one side of the derrick floor while work is going on. It is

used for swabbing etc.

The load and service requirement on the sand line are very light compared to

the drilling line allowing smaller & less expensive lines to be used for this

purpose. Normally, 7/6� to 5/8� steel cables are used as sand line.

w- 4

PARTS OF A WORKOVER RIG

1. Hook

2. Fast Line

3. Dead Line

4. Monkey Board

5. Traveling Block

6. Grown Block

a) Move-in (b) Rig-up (c) Rig Down are carried out by a workover rig

when we go from one well to another.

Rigs are moved from one location to another one, on roads. If there is

no road, a temporary road is constructed for the movement.

The foundation under the Derrick legs must support the hook loads and the

weight of the derrick.

Failure of the foundation under one leg can cause failure of the derrick at

much less than the rated capacity.

Positioning of the rig must be fairly precise in order that the hook is centered

over the wellhead without excessive adjustment of the derrick.

Leveling is done by hydraulic jacks.

There are many reasons which make workover necessary or/ and inviting

They are:

1. Water shut-off jobs

2. Transfer to different zones.

w- 5

3. setting of packers

4. Abandoning a well.

5. Well servicing, stimulation and activation

6. Installation of pumps

7. Gravel pack

8. Fishing jobs.

For carrying out above jobs, a lot of infomations are needed for planning.

They are:

A. Casing: Size and type of casings, condition of casing, top of cement

etc.

B. Tubing: Size and type, General condition, auxiliary equipment like

packers, Safety joint etc.

C. Well head: Type and pressure rating, casing head flange etc.

D. Production history of the well.

E. Log & core records

F. Water analysis.

G. Record of previous remedial work.

After an workover, an economic analysis should be carried out as to the gain

in oil (before and after) or the objective has been fulfilled or not.

WORKOVER INDEX: It is defined as the workover carried out one

workerover per rig per year.

w- 6

Operations carried out at any oil and gas well with a view to maintain or

improve production/injection is known as work over operations, For these

operations smaller size rigs are utilised which are known as work over

rigs.

These operations are necessiated from the fact that most of the oil and

gas wells sonner or later starts behaving erratically and production of oil

and gas starts going down, water/sands production comes up. Work over

operations are necessary for maintaining or increasing the production of

oil and gas.

MINOR WORKOVER OPERAIONS.

1. Well bottom cleaning � If a bottom of a well is occupied by sand or mud

settlements, it needs to be cleared by jetting action or some time by

drilling.

2. Scraping of paraffin - From inside walls of the

casing:-

Before running any tool inside a well, the casing is required to be scraped of

any paraffin depositions so as to avoid any stuck up of tools etc. For this,

casing scrapers are run.

3. Oil circulation �Some times to give extra boost, well fluid is displaced

with oil.

4. Surfactant treatment-To remove blockade against the perforation,

surfactant treatment is given which helps removal of the water blocks by

reducing the interface surface tension.

5. Installation or servicing of artificial lift equipments such as, sucker rod

pumps, submersible pumps, plunger lift pumps etc.

w- 7

6. Wire line operations including manipulation of side pocket mandrel,

regulation of bottom hole choke.

MAJOR WORKOVER OPERAIONS WILL MOSTLY CONSIST OF:

1. Production workvoer operations as

i. Water shut off jobs.

ii. Gas shut off jobs

iii. Maintenance or improving production by stimulation techniques.

2. Repair work over jobs

i. Repair of leaking or parted casing or replacement of casing

ii. Repair of bad cementation behind casing.

3. Recompletion workover job such as recompletions in new horizon or

horizons or converting a well from a producing one to injection well.

A little details of the major workover jobs

1. Water shut off jobs-some times alongwith oil, water also starts coming.

This may be due to any one or combination of more than one of the

followings reasons.

a. Water zone may be near to perforations.

b. Channeling behind casing due to bad cementation.

c. Water coning or fingering.

d. Early break through of water in highly permeable beds

e. Casing leak against water zone

w- 8

Detection - By isotope injection, production logging such as temperature log,

density log etc.

Remedy -i. Squeeze cementation for leakage of casing or channeling

behind casing.

ii. Regulate productions to prevent water coning or

fingering.

iii. Seal perforations near water zone.

2. Gas shut off-High GOR and high gas production.

a. Channeling behind casing

b. Casing leakage against a gas zone

c. Gas coning due to high vertical permeability

d. Perforations near oil/gas contact

e. Depletion below saturations pressure.

Detection - By neutron log and temperature log.

Remedy - a. Squeeze cementation for leakage in casing or channeling in

cement behind casing.

b. Sealing the perforations near oil/gas contacts.

c. Regulating production to avoid coning.

WORKOVER TO IMPROVE PRODUCTION.

Some times due to scale formations against the perforations production of oil and gas goes down. This scale formation may be due to mud cake, shale, paraffin or swelling of shale which plugs the channels of flow. Detection

w- 9

The pressure build-up study shows the extent of skin (damage due to scale

deposition against the perforations) around the well bore, A negative skin is

indicative of good permeability around the well bore . Positive skin is

indicative of scale deposition.

Remedy:

Methods to improve production

1. Reperforation or additional perforation. Additional chaanels are created

for flow of oil & gas.

2. Stimulation of well bore perforation and producing horizons. Stimulation

can be done by

a. Acidization

b. Hydro fracturing

c. Acid frac

d. Hydroperforation

Acidisation :

Depending upon nature of damage and type of formation the acid jobs are

planned.

For carbonate reservoirs, hydrochloric acid treatment is given, however in

case of sandstone reservoir or mud cake problems mud acid treatment is

resorted to.

Fracturing

In case of very tight and low permeability formations fracturing is

resorted to. By this technique, artificial channels are created in the

formation. Alongwith hydro-fracturing fluid some propping agents like

w- 10

sand, bauxite beads etc. are also used which prevents the strata to

come back to original position.

Acid Frac- In some cases fracturing is done with the acid solution as fracturing

fluid to get better flow channels. In such cases propping agents are not

needed.

Hydroperforation-

When normal method of perforations does not give better results,

hydroperforation is done. This technique makes use of jet action of

hydraulic fluid added with sand which abrades and helps penetration. With

this jet the well bore can also be cleared

Repair by workover -

Casing leaks. Casing leaks can occur due to corrosion, abrasion,

damage of threads near casing joints etc. Casing leaks can be detected by

hermetical test and then located by setting ret. Packers at different points.

Leakpoint can also be located by injecting isotopes and running radio active

log.

Remedy.

1. Normally, most of the leak cases can be tackled by squeeze cementation.

2. In case of badly leaking or parted casing, replacement of casing becomes necessary. For this, a plug is put below the leaking point and .casing is cut above the plug but below the leak point and pulled out.

3. In case of collapsed casing, roller may restore it back.

w- 11

Repair of defective cementation : Defective cementation causes water or gas channeling, which

effects the production adversely. Cement bond log indicates the portions

behind casing where cement bonding is not alright.

Such types of defects can be repaired by

a. Cement squeeze job.

b. Block cement job.

a. Cement Squeeze job

Cement slurry or diesel cement slurry is injected through the perforations.

If required, after squeeze cement job additional perforations can be done.

b. Block cementation

A short of annular cement block is created behind the casing near the

suspected bad cementations portion. For this purpose perforations are done

against the shale formation below the producing sand horizon. A cement

retainer is set in between those two sets of perforations. Thereafter

cement is pumped through the cement retainer.

Transfer of horizons -

In multilayered reservoirs, if one horizon has stopped producing then a plug

can be put .above this and another horizon can be opened in usual way as if

a new well. Some times a similar well can be used for injection purposes.

w- 12

Sand Control - A technique with the help of workover rig.

Production of loose sand will adversely affect the tubulars and production

equipment. Also deposition of loose sand at the bottom will block the well

and production may stop. Production of sand can be prevented by.

a. Slotted screen liner with gravel packing across

the perforation. Slotted screen liner can also be wire

wrapped.

b. Consolidating sand by injecting liquid plastic.

DEFICIENCY FOUND IN B.OP. AT WORKOVER RIGS. 1. B.O.P has only handwheels for closing the wells.

2. Handwheels not attached to RAM locks

3. No checking for cracks etc. in adapter spools

4. Use of old ring gaskets that are pitted or mashed.

5. No safety valve available

6. No backpressure valve available.

7. Set-up cement in some lines and valves in manifold

8. Pipes not anchored against vibration.

9. No support for choke and kill lines which have heavy valves installed.

10. Safety valve wrench not readily available.

11. Crews not knowing even the obvious signs of kicks or blowouts.

12. No knowledge of burst rating of casing (or whether it should be derated

because of mechanical abuse or corrosion).

w- 13

13. Failure to go to bottom when opportunity permits in course of threatened

kick or blowout.

14. Using studs and nuts with mashed threads.

15. Trying to circulate a kick out with constant pit level.

Every well drilled in high formation-blowout is considered a hazard till

X�mas tree is fitted

Most blowouts can be avoided � if men on the Job are familiar with warning

signs and know the procedures to follow for controlling well pressure.

Early recognition of signs of blowout is important.

Signs are:

i. Flow of fluid from the well.

ii. Rise in pit level

iii. Decrease in circulation pressure.

iv. Shows of oil, gas and salt water in the mud.

After detection, action must be taken to regain a column of mud heavy

enough to contain well pressure. Although various means might be

employed to accomplish this, two actions are necessary.

i. The well is closed-in by closing blowout preventers and chokes.

ii. The extreneous fluid that has entered the wellbore is circulated out.

w- 14

CARE AND INSPECTION OF WIRE ROPES.

Lack of attention towards rope inspection and maintenance- Failure of a wire

rope.

Wire rope- used as a link in transmission of power from the power unit to

work, is just as much a part of the machine as the pumps, valves, cylinders

etc. and deserves the same attention to lubrication and inspection as any

other part of the machine. Replace a wire rope which shows signs of

weakness which might lead to its sudden failure. The particular types of wire

rope for each application has been selected on the basis of wire rope

manufacturer�s recommendation and field experience. Use a rope of the

recommended diameter and cut it to the correct length. A rope which is too

long will be damaged by over winding and a rope that is too short may pull

out of its attachment with serious results. Ropes should be kept on frame

works in the case of ropes on drums, and should be inspected frequently and

coated with rope dressing. Examine the entire rope end-to-end for evidence

of external damage or abuse.

Determine the exact cause of external damage.

Check for broken wires, corrosion and condition of fitting

W-15

FISHING AND FISHING TOOLS

Any object that obstructs the hole or impedes further drilling or running of

pipe is called a Fish, and removing this obstruction or correcting the problem

is called FISHING. Since fishing is required up to 20 % of all drilling jobs and

80 % of all workover jobs, the skills and tools required form a sizeable service

industry.

The term �fishing� applies to all operations concerned with retrieving of

equipment or other objects from a well.

Portions of the drill string, bit, drill string accessories and inadvertently

dropped handtools are typical items which may require fishing. The most

common fishing job is that of recovering a portion of the drill string left in the

hole due to either its failure or becoming stuck.

The choice of fishing tools and equipment is dictated by the size and shape of

the fish, the anticipated severity of the problem and the experience of the

fisherman.

Fishing tools are quite numerous and only a qualitative description of a few

basic types will be attempted here.

W-16

1 OVERSHOT: These are cylindrical bowl shaped tools which telescope

over the fish. An internal slip arrangement grasps the outside of the fish

with the grip tightening as pull is increased. Modern overshots have a

releasing mechanism to be used if the fish cannot be pulled.

2 SPEARS: These devices pass inside the fish, grasping its inner wall with

expanding slips, which can be set or released by rotating the pipe. Spears

are generally used when the hole clearance will not tolerate an overshot.

Their principal advantage over the tapered tap is their releasing

mechanism.

3 TAPERED TAPS: These are among the oldest fishing tools used in

drilling. The tap is run into the fish and rotated until sufficient threads are

cut for a firm hold.

4 WASHOVER PIPE: This is a section of pipe having sufficient inside

diameter to telescope outside the fish. It is used when annular cleaning

around the fish is required.

5 INSIDE & OUTSIDE CUTTERS: These are pipe cutters which can be

actuated by surface manipulation of the drill pipe. Inside cutters, cut the

fish from the inside out, while outside cutters do the reverse.

6 MAGNETS : Loose junk, such as bit cones and hand tool, is frequently

lost in the hole and impedes drilling until it is eliminated knowing what is

lost in the hole is always helpful, as it may be possible to duplicate the

situation on the surface and actually try the tools being considered.

W-17

Specific tools used are magnets, junk baskets, carbide mills, or some tool

specifically designed for the problem.

Permanent magnets are very effective if there is enough surface on the fish for

good contact. Magnets are made with circulating ports, opening around the

outer edge of the tool so that they can be washed down the hole. They should

always be run on pipe so that the fill on top of the fish can be washed away

and actual contact made.

7 CARBIDE MILLS : Tungsten carbide mills are one if the most

innovative items added to fishing tools in the last three decades. The sharp

tungsten carbide particles are set in a matrix of alloyed bronze. Then they

are applied to a steel mill, when properly run, cuts a tremendous amount of

steel. Normally it is turned fast, perhaps one-third to one-half faster than a

similar sized rock bit.

8 JUNK SHOTS: Junks shots are used occasionally to break up a large

piece of junk that cannot be retrieved. The shot is a large shaped charge

made to direct the major force downward. Since all of the forces cannot be

directed down, junk shots should never be run inside casing as the

explosion will split and destroy the pipe.

These shots are usually quite effective in breaking the junk into pieces small

enough to be fished with a magnet or a junk basket. Junk shots are run on drill

pipes.

w- 1

Primary recovery depends upon natural reservoir energy to drive the oil

through a complex pore network to producing wells. With the passage of

time, the producing wells for various reasons become sick and a steep fall in

their production levels is registered. To repair these sick wells and rejuvenate

oil production from them, work over operations are carried out.

The primary objective of workover operation is to maintain the wells in

optimum producing condition.

The rig which is smaller for doing this job is called �WORKOVER RIG�.

This rig is smaller than the drilling rig as far as capacity, height, leg spacings

etc are concerned.

In addition to solving specific well and reservoir control problems,

workovers can provide a check on lateral and vertical movement & current

location of oil, water & gas in specific zones & reservoirs.

Surface Equipments of a standard workover Rig

1. Rotary Table. 2. Prime movers. 3. Derrick 4. Substructure. 5. Drawworks

6. Mud Pumps. 7. Blow out preventers

1. ROTARY TABLE: - The rotary table has two primary functions.

a) It transmits the rotation to the drill string by turning the Kelly joint.

b) It suspends the pipe weight during connections & trips

Normally, the table is chain-driven through the draw works, although a

smaller separate engine is sometimes used as an independent unit.

2. PRIME MOVERS: - Currently I.C engines are the most common.

id5392734 pdfMachine by Broadgun Software - a great PDF writer! - a great PDF creator! - http://www.pdfmachine.com http://www.broadgun.com

w- 2

3. DERRICK:- The derrick is the structure which affords the vertical

clearance necessary for conducting such operations as running in &

pulling out of tools and tubings. It must be strong enough to withstand the

loads imposed upon it.

These loads vary with depth and the size of hole and casing.

An attempt to reduce operating costs now-a-days, portable unitized rigs are

being used. The entire rig is mounted either on skid or trailer for maximum

portability.

The principal advantages are savings in transportation costs & rig up.

4. SUB-STRUCTURE:- The substructure, as the name implies, is the

support on which the derrick rests. This must be of sufficient strength to

support the anticipated loads with adequate safety factor. Its height must

be sufficient to house & afford access to the blow out preventors.

5. DRAW-WORKS: The draw works or hoist is the key piece of

equipment. Its functions are:

a) It is the control centre from which the driller operates the rig. It

contains the clutches, chains, sprockets & other controls which enable

the rig power to be diverted to the particular operation at hand.

b) It houses the drum which spools the drilling line during hoisting

operations and also feed-off, during running-in. Draw-works are

commonly designated by a horse-power and depth rating.

6. MUD PUMPS: The function of the mud or slush pump is to circulate the

drilling fluid at the desired pressure and volume. The pump normally

used for this service is the reciprocating pump, double acting, duplex

type. Pumps are commonly rated by hydraulic horse power.

w- 3

7. BLOW OUT PREVENTERS : it is not always possible to predict the

exact magnitude of pressures which will be encountered while doing a

job in the well consequently, it is not uncommon to encounter pressure

greater than those imposed by the drilling fluid , with the result that

formation fluids flow into the borehole and eventually to the surface. This

effect is called a blow-out and this can be checked by means of blowout

preventor. Its function is to close the annulus between two concentric

pipes.

Most of them are hydraulically or pneumatically operated, manual operation

available as a safety precaution. The pressure rating of blow out preventers is

dictated by the hazards of the area and depth in which they are used.

DRILLING LINE: It is the wire rope which is spooled on the drum of the

draw work hoist, reeved on the crown block and traveling block and used in

hoisting tubings in making a trip.

SAND LINE : The sandline is spooled on the sand reel, passed over a

sheave at the top of the derrick and is normally attached to a bailer which

stands vertically to one side of the derrick floor while work is going on. It is

used for swabbing etc.

The load and service requirement on the sand line are very light compared to

the drilling line allowing smaller & less expensive lines to be used for this

purpose. Normally, 7/6� to 5/8� steel cables are used as sand line.

w- 4

PARTS OF A WORKOVER RIG

1. Hook

2. Fast Line

3. Dead Line

4. Monkey Board

5. Traveling Block

6. Grown Block

a) Move-in (b) Rig-up (c) Rig Down are carried out by a workover rig

when we go from one well to another.

Rigs are moved from one location to another one, on roads. If there is

no road, a temporary road is constructed for the movement.

The foundation under the Derrick legs must support the hook loads and the

weight of the derrick.

Failure of the foundation under one leg can cause failure of the derrick at

much less than the rated capacity.

Positioning of the rig must be fairly precise in order that the hook is centered

over the wellhead without excessive adjustment of the derrick.

Leveling is done by hydraulic jacks.

There are many reasons which make workover necessary or/ and inviting

They are:

1. Water shut-off jobs

2. Transfer to different zones.

w- 5

3. setting of packers

4. Abandoning a well.

5. Well servicing, stimulation and activation

6. Installation of pumps

7. Gravel pack

8. Fishing jobs.

For carrying out above jobs, a lot of infomations are needed for planning.

They are:

A. Casing: Size and type of casings, condition of casing, top of cement

etc.

B. Tubing: Size and type, General condition, auxiliary equipment like

packers, Safety joint etc.

C. Well head: Type and pressure rating, casing head flange etc.

D. Production history of the well.

E. Log & core records

F. Water analysis.

G. Record of previous remedial work.

After an workover, an economic analysis should be carried out as to the gain

in oil (before and after) or the objective has been fulfilled or not.

WORKOVER INDEX: It is defined as the workover carried out one

workerover per rig per year.

w- 6

Operations carried out at any oil and gas well with a view to maintain or

improve production/injection is known as work over operations, For these

operations smaller size rigs are utilised which are known as work over

rigs.

These operations are necessiated from the fact that most of the oil and

gas wells sonner or later starts behaving erratically and production of oil

and gas starts going down, water/sands production comes up. Work over

operations are necessary for maintaining or increasing the production of

oil and gas.

MINOR WORKOVER OPERAIONS.

1. Well bottom cleaning � If a bottom of a well is occupied by sand or mud

settlements, it needs to be cleared by jetting action or some time by

drilling.

2. Scraping of paraffin - From inside walls of the

casing:-

Before running any tool inside a well, the casing is required to be scraped of

any paraffin depositions so as to avoid any stuck up of tools etc. For this,

casing scrapers are run.

3. Oil circulation �Some times to give extra boost, well fluid is displaced

with oil.

4. Surfactant treatment-To remove blockade against the perforation,

surfactant treatment is given which helps removal of the water blocks by

reducing the interface surface tension.

5. Installation or servicing of artificial lift equipments such as, sucker rod

pumps, submersible pumps, plunger lift pumps etc.

w- 7

6. Wire line operations including manipulation of side pocket mandrel,

regulation of bottom hole choke.

MAJOR WORKOVER OPERAIONS WILL MOSTLY CONSIST OF:

1. Production workvoer operations as

i. Water shut off jobs.

ii. Gas shut off jobs

iii. Maintenance or improving production by stimulation techniques.

2. Repair work over jobs

i. Repair of leaking or parted casing or replacement of casing

ii. Repair of bad cementation behind casing.

3. Recompletion workover job such as recompletions in new horizon or

horizons or converting a well from a producing one to injection well.

A little details of the major workover jobs

1. Water shut off jobs-some times alongwith oil, water also starts coming.

This may be due to any one or combination of more than one of the

followings reasons.

a. Water zone may be near to perforations.

b. Channeling behind casing due to bad cementation.

c. Water coning or fingering.

d. Early break through of water in highly permeable beds

e. Casing leak against water zone

w- 8

Detection - By isotope injection, production logging such as temperature log,

density log etc.

Remedy -i. Squeeze cementation for leakage of casing or channeling

behind casing.

ii. Regulate productions to prevent water coning or

fingering.

iii. Seal perforations near water zone.

2. Gas shut off-High GOR and high gas production.

a. Channeling behind casing

b. Casing leakage against a gas zone

c. Gas coning due to high vertical permeability

d. Perforations near oil/gas contact

e. Depletion below saturations pressure.

Detection - By neutron log and temperature log.

Remedy - a. Squeeze cementation for leakage in casing or channeling in

cement behind casing.

b. Sealing the perforations near oil/gas contacts.

c. Regulating production to avoid coning.

WORKOVER TO IMPROVE PRODUCTION.

Some times due to scale formations against the perforations production of oil and gas goes down. This scale formation may be due to mud cake, shale, paraffin or swelling of shale which plugs the channels of flow. Detection

w- 9

The pressure build-up study shows the extent of skin (damage due to scale

deposition against the perforations) around the well bore, A negative skin is

indicative of good permeability around the well bore . Positive skin is

indicative of scale deposition.

Remedy:

Methods to improve production

1. Reperforation or additional perforation. Additional chaanels are created

for flow of oil & gas.

2. Stimulation of well bore perforation and producing horizons. Stimulation

can be done by

a. Acidization

b. Hydro fracturing

c. Acid frac

d. Hydroperforation

Acidisation :

Depending upon nature of damage and type of formation the acid jobs are

planned.

For carbonate reservoirs, hydrochloric acid treatment is given, however in

case of sandstone reservoir or mud cake problems mud acid treatment is

resorted to.

Fracturing

In case of very tight and low permeability formations fracturing is

resorted to. By this technique, artificial channels are created in the

formation. Alongwith hydro-fracturing fluid some propping agents like

w- 10

sand, bauxite beads etc. are also used which prevents the strata to

come back to original position.

Acid Frac- In some cases fracturing is done with the acid solution as fracturing

fluid to get better flow channels. In such cases propping agents are not

needed.

Hydroperforation-

When normal method of perforations does not give better results,

hydroperforation is done. This technique makes use of jet action of

hydraulic fluid added with sand which abrades and helps penetration. With

this jet the well bore can also be cleared

Repair by workover -

Casing leaks. Casing leaks can occur due to corrosion, abrasion,

damage of threads near casing joints etc. Casing leaks can be detected by

hermetical test and then located by setting ret. Packers at different points.

Leakpoint can also be located by injecting isotopes and running radio active

log.

Remedy.

1. Normally, most of the leak cases can be tackled by squeeze cementation.

2. In case of badly leaking or parted casing, replacement of casing becomes necessary. For this, a plug is put below the leaking point and .casing is cut above the plug but below the leak point and pulled out.

3. In case of collapsed casing, roller may restore it back.

w- 11

Repair of defective cementation : Defective cementation causes water or gas channeling, which

effects the production adversely. Cement bond log indicates the portions

behind casing where cement bonding is not alright.

Such types of defects can be repaired by

a. Cement squeeze job.

b. Block cement job.

a. Cement Squeeze job

Cement slurry or diesel cement slurry is injected through the perforations.

If required, after squeeze cement job additional perforations can be done.

b. Block cementation

A short of annular cement block is created behind the casing near the

suspected bad cementations portion. For this purpose perforations are done

against the shale formation below the producing sand horizon. A cement

retainer is set in between those two sets of perforations. Thereafter

cement is pumped through the cement retainer.

Transfer of horizons -

In multilayered reservoirs, if one horizon has stopped producing then a plug

can be put .above this and another horizon can be opened in usual way as if

a new well. Some times a similar well can be used for injection purposes.

w- 12

Sand Control - A technique with the help of workover rig.

Production of loose sand will adversely affect the tubulars and production

equipment. Also deposition of loose sand at the bottom will block the well

and production may stop. Production of sand can be prevented by.

a. Slotted screen liner with gravel packing across

the perforation. Slotted screen liner can also be wire

wrapped.

b. Consolidating sand by injecting liquid plastic.

DEFICIENCY FOUND IN B.OP. AT WORKOVER RIGS. 1. B.O.P has only handwheels for closing the wells.

2. Handwheels not attached to RAM locks

3. No checking for cracks etc. in adapter spools

4. Use of old ring gaskets that are pitted or mashed.

5. No safety valve available

6. No backpressure valve available.

7. Set-up cement in some lines and valves in manifold

8. Pipes not anchored against vibration.

9. No support for choke and kill lines which have heavy valves installed.

10. Safety valve wrench not readily available.

11. Crews not knowing even the obvious signs of kicks or blowouts.

12. No knowledge of burst rating of casing (or whether it should be derated

because of mechanical abuse or corrosion).

w- 13

13. Failure to go to bottom when opportunity permits in course of threatened

kick or blowout.

14. Using studs and nuts with mashed threads.

15. Trying to circulate a kick out with constant pit level.

Every well drilled in high formation-blowout is considered a hazard till

X�mas tree is fitted

Most blowouts can be avoided � if men on the Job are familiar with warning

signs and know the procedures to follow for controlling well pressure.

Early recognition of signs of blowout is important.

Signs are:

i. Flow of fluid from the well.

ii. Rise in pit level

iii. Decrease in circulation pressure.

iv. Shows of oil, gas and salt water in the mud.

After detection, action must be taken to regain a column of mud heavy

enough to contain well pressure. Although various means might be

employed to accomplish this, two actions are necessary.

i. The well is closed-in by closing blowout preventers and chokes.

ii. The extreneous fluid that has entered the wellbore is circulated out.

w- 14

CARE AND INSPECTION OF WIRE ROPES.

Lack of attention towards rope inspection and maintenance- Failure of a wire

rope.

Wire rope- used as a link in transmission of power from the power unit to

work, is just as much a part of the machine as the pumps, valves, cylinders

etc. and deserves the same attention to lubrication and inspection as any

other part of the machine. Replace a wire rope which shows signs of

weakness which might lead to its sudden failure. The particular types of wire

rope for each application has been selected on the basis of wire rope

manufacturer�s recommendation and field experience. Use a rope of the

recommended diameter and cut it to the correct length. A rope which is too

long will be damaged by over winding and a rope that is too short may pull

out of its attachment with serious results. Ropes should be kept on frame

works in the case of ropes on drums, and should be inspected frequently and

coated with rope dressing. Examine the entire rope end-to-end for evidence

of external damage or abuse.

Determine the exact cause of external damage.

Check for broken wires, corrosion and condition of fitting

W-15

FISHING AND FISHING TOOLS

Any object that obstructs the hole or impedes further drilling or running of

pipe is called a Fish, and removing this obstruction or correcting the problem

is called FISHING. Since fishing is required up to 20 % of all drilling jobs and

80 % of all workover jobs, the skills and tools required form a sizeable service

industry.

The term �fishing� applies to all operations concerned with retrieving of

equipment or other objects from a well.

Portions of the drill string, bit, drill string accessories and inadvertently

dropped handtools are typical items which may require fishing. The most

common fishing job is that of recovering a portion of the drill string left in the

hole due to either its failure or becoming stuck.

The choice of fishing tools and equipment is dictated by the size and shape of

the fish, the anticipated severity of the problem and the experience of the

fisherman.

Fishing tools are quite numerous and only a qualitative description of a few

basic types will be attempted here.

W-16

1 OVERSHOT: These are cylindrical bowl shaped tools which telescope

over the fish. An internal slip arrangement grasps the outside of the fish

with the grip tightening as pull is increased. Modern overshots have a

releasing mechanism to be used if the fish cannot be pulled.

2 SPEARS: These devices pass inside the fish, grasping its inner wall with

expanding slips, which can be set or released by rotating the pipe. Spears

are generally used when the hole clearance will not tolerate an overshot.

Their principal advantage over the tapered tap is their releasing

mechanism.

3 TAPERED TAPS: These are among the oldest fishing tools used in

drilling. The tap is run into the fish and rotated until sufficient threads are

cut for a firm hold.

4 WASHOVER PIPE: This is a section of pipe having sufficient inside

diameter to telescope outside the fish. It is used when annular cleaning

around the fish is required.

5 INSIDE & OUTSIDE CUTTERS: These are pipe cutters which can be

actuated by surface manipulation of the drill pipe. Inside cutters, cut the

fish from the inside out, while outside cutters do the reverse.

6 MAGNETS : Loose junk, such as bit cones and hand tool, is frequently

lost in the hole and impedes drilling until it is eliminated knowing what is

lost in the hole is always helpful, as it may be possible to duplicate the

situation on the surface and actually try the tools being considered.

W-17

Specific tools used are magnets, junk baskets, carbide mills, or some tool

specifically designed for the problem.

Permanent magnets are very effective if there is enough surface on the fish for

good contact. Magnets are made with circulating ports, opening around the

outer edge of the tool so that they can be washed down the hole. They should

always be run on pipe so that the fill on top of the fish can be washed away

and actual contact made.

7 CARBIDE MILLS : Tungsten carbide mills are one if the most

innovative items added to fishing tools in the last three decades. The sharp

tungsten carbide particles are set in a matrix of alloyed bronze. Then they

are applied to a steel mill, when properly run, cuts a tremendous amount of

steel. Normally it is turned fast, perhaps one-third to one-half faster than a

similar sized rock bit.

8 JUNK SHOTS: Junks shots are used occasionally to break up a large

piece of junk that cannot be retrieved. The shot is a large shaped charge

made to direct the major force downward. Since all of the forces cannot be

directed down, junk shots should never be run inside casing as the

explosion will split and destroy the pipe.

These shots are usually quite effective in breaking the junk into pieces small

enough to be fished with a magnet or a junk basket. Junk shots are run on drill

pipes.