this is brief introduction about well completions and workovers by request of students for education purposes

1. Introduction to Workovers and Completions
1
Completions - Categorized By a Few Basic Criteria
Wellbore and Producing Formation Interface
Open Hole or Cased Hole
Production Method
Flowing (high pressure/low pressure)
Secondary Recovery (pumping, gas lift, plunger lift)
Number of Completed Zones
Single or Multiple

2. Introduction to Workovers and Completions
2
Open Hole
Completion
Advantages of an open hole completion:
Simple, fast, and inexpensive
Provides for more surface area of the pay to be
exposed to the wellbore
No perforating required
Casing costs are drastically reduced
The well design easily lends itself to deepening
Disadvantages of an open hole completion:
Well control can be complicated due to the massive
fluid loss to the producing formation
Not recommended for formations that are layered
and have varying permeability
Casing may need to be set before the pay is drilled
or logged

3. Introduction to Workovers and Completions
3
Cased Hole
Completion
Flowing
Well
A flowing well is one which flows hydrocarbons to
the surface using naturally-occurring formation
pressure as the driving force.
A formation pressure need not be very great to flow
hydrocarbons to the surface. Gas, being a very light
fluid does not require a great deal of pressure to
overcome its hydrostatic pressure. Conversely, oil,
being considerably denser than gas, requires more
minimal formation pressure than gas to flow to the
surface.
A flowing well generally has the lowest lifting costs
therefore making it more profitable than a well using
a secondary recovery method.

4. Introduction to Workovers and Completions
4
Secondary
Recovery
Cased Hole
Completion Injection Gas
Produced Oil
Pumping wells and wells
using gas lift are usually in
the category of secondary
recovery.
Secondary recovery
methods are those
employed after formation
pressure has decreased to
the point that produced
fluid hydrostatic pressure
equals formation pressure.
When this occurs the well
ceases to produce
naturally.
Produced Oil

5. Introduction to Workovers and Completions
5
Secondary
Recovery
Cased Hole
CompletionAnother form of secondary recovery utilizes injected gas or liquids to maintain, enhance, or
regain production from a depleting formation.
Injection Well
Producing Well Producing Well

6. Introduction to Workovers and Completions
6
Secondary
Recovery
Cased Hole
Completion
A third means of secondary recovery is in the form of an
electrically-powered submursible pump. Submursible
pumps are available in a range of sizes depending on
whether the pump is to be run in the casing or tubing.
They are also available in a range of pumping capacities
based on the fluids to be produced and the potential
productivity of the well into which they are to be used.
To Electrical Supply

7. Introduction to Workovers and Completions
7
Cased Hole
Completion
Single and Multi-Zone
Completions
Depending on local subsurface
geology, wells may be drilled and
completed into either single or
multiple pay zones.
Multiple pay zones can be completed
as dual completions as the well on
the right, but can also be completed
as single string completions.

8. Introduction to Workovers and Completions
8
Repair Mechanical Damage
Mechanical damage comes in many
forms:
Failed or failing wellheads
Failed safety valves
Gas lift equipment
Worn tubing Nipples
Failed Sliding sleeves
Leaking Packers
Holes in the tubing
Failed Casing
In some instances the repair can be
performed without killing the well
and done with some form of well
servicing unit. In other cases the
well has to be killed and a rig put
on the well to remove all tubulars
and tools and then be reinstalled
with refurbished or new equipment.
Reasons For
Workovers
Failed Wellhead
Failed Safety Valve
Failed Gas Lift Equipment
Worn Tubing Nipple
Failed Sliding Sleeve
Failed Packer
Hole In Tubing

9. Introduction to Workovers and Completions
9
Reservoir stimulation is a process in which a
mild acid is introduced through the perfs and
into an existing producing reservoir. The
purpose is to dissolve acid-soluble solids
which usually “opens” clogged permeability
and regains or restores production.
Stimulation can be done by bullheading,
using a coiled tubing unit, snubbing unit, or
small tubing unit.
Reservoir Stimulation
Reasons For
Workovers

10. Introduction to Workovers and Completions
10
Gravel Packing or Repairing A Gravel
Pack
A gravel pack completion is used where
the producing formation lacks sufficient
consolidation to withstand the friction
caused by fluid flow from the formation
to the wellbore.
A slurry of “sand” and viscous liquid is
pumped down the workstring and into
the annular space between the casing
and the screen until it is filled, or
“sands out.” Excess sand slurry
remaining in the workstring is reversed
out.
Another similar operation, known as a
frac pack, involves pumping the sand
slurry at high rates forcing the mixture
far out into the producing formation.
Reasons For
Workovers
Sump Packer
Gravel Pack
Packer

11. Introduction to Workovers and Completions
11
Here the lower depleted zone has been isolated with a
plug conveyed by either coiled tubing or wireline. After
the plug has been successfully set and tested the sliding
sleeve is opened allowing production from the upper
zone.
Accessing A New Reservoir
Plug set in tubing nipple
Open sliding sleeve
When a well is drilled through multiple producing
zones and completed with a single production string it
is common to produce the lower zone first. Upon
depletion of the lower zone, the upper zone is then
produced.
This can be done in a variety of ways but usually
entails abandoning the lower zone before production
begins from the upper zone.
Reasons For
Workovers

12. Introduction to Workovers and Completions
12
Another means of completing a new reservoir:
Cut the production tubing just above the packer
with an electric line or coiled tubing conveyed
tubing cutter
Set and test a cement plug above the packer
Perforate the new zone and begin production
Reasons For
Workovers
Accessing A New Reservoir

13. Introduction to Workovers and Completions
13
Completing Multiple Reservoirs
A dual completion, such as this one, allows
for production from two zones simultaneously
through two separate strings of tubing. The
deeper string is commonly referred to as the
long string while the shallower tubing string is
known as the short string.
Reasons For
Workovers

14. Introduction to Workovers and Completions
14
Unwanted Water Production
Water
Oil
Water, if present in a
producing formation, is
the lowermost fluid due
to its density. And if the
presence of water is
known, a well will be
completed above the oil-
to-water contact.
As the well is produced
is conducted, the oil-to-
water contact rises and
eventually the water
invades the lower perfs
resulting in unwanted
water production.
Water
Oil
Reasons For
Workovers

15. Introduction to Workovers and Completions
15
Unwanted Gas Production
Additionally, the drive
mechanism is being
depleted which will
shorten the duration of the
flowing phase of the well.
This can be temporarily
remedied by squeezing
cement into the perfs. But
eventually mostly gas will
be produced as the
producible oil is depleted.
In a gas cap driven
reservoir, the gas cap
expands as oil is
produced. Eventually the
expanding gas cap
encroaches on the
perforations and gas
production will begins.
The drawbacks are: the
drive mechanism is being
produced and the
production train may not
be able to handle the gas
being produced.
Reasons For
Workovers
Gas
Oil
Gas
Oil

16. Introduction to Workovers and Completions
16
Water
Oil
Unwanted Water Production
Squeezing The Perfs
Reasons For
Workovers
The usual remedy for unwanted gas or
water production is to squeeze the perfs
with cement in hopes that the “watered-
out” perfs will be plugged and the water
production decreased.
The process entails identifying the
affected perfs then running an setting a
squeeze packer just above the affected
perfs. Cement is them pumped down the
workstring and into the perfs.

17. Introduction to Workovers and Completions
17
Water Coning
Excessive production rates
in a water driven formation
can create a condition
known as water coning.
Water coning results in
water being pulled up into
the perfs.
Water production will usually
continue so long as the well
produces regardless of the
production
Decreasing the production
rate, a commonly tried
technique, rarely reduces
the water production.
The “quick fix” is to locate
and block squeeze the
affected perfs and decrease
production rate.
Reasons For
Workovers
GAS
Water
Oil
Water Coning

18. Introduction to Workovers and Completions
18
Repair Failed Cement Jobs
Evidence of a failing cement job
usually manifests as pressure
appearing on the intermediate casing
string and the presence of chunks of
cement in the choke body. This may
also be accompanied by a decrease in
daily production as surface lines can
become clogged with cement.
Repairing this usually entails killing
the well, squeezing cement into the
perforations, recompleting and
reperforating the well.
Reasons For
Workovers

19. Introduction to Workovers and Completions
19
Pack-Off A Hole In The Tubing Or Casing
Reasons For
Workovers
Upper Slip Stop
Lower Slip Stop
Upper Pack-Off
Lower Pack-Off
Spacer Pipe
If a hole in wellbore tubulars develops, a workover
can be temporarily postponed by running a tubing
pack-off. This can be done on slickline, coiled
tubing, or small jointed pipe, but is commonly
conveyed in slickline.

20. Introduction to Workovers and Completions
20
Tubing String Replacement
During the life of a well it may become necessary to
replace the entire tubing string due to excessive
wear.
Wear can be in the form of erosional wear caused by
sand production or pitting and corrosion caused by
hydrogen sulfide or carbon dioxide.
Premature failure can also occur due to excessive
hole deviation.
Reasons For
Workovers

21. Introduction to Workovers and Completions
21
Artificial Lift Installation – Rod Pump
Weatherford Downhole Rod Pump
Walking Beam Horsehead
Bridle
Polished Rod
Wellhead and Stuffing Box
In pumping installations, points of wear
include the rods, tubing string, and the
downhole pump.
Reasons For
Workovers

22. Introduction to Workovers and Completions
22
The Plunger Lift System consist of a plunger,
piston, two bumper springs, a lubricator to sense
and stop the plunger as it arrives at the surface,
and one of several different styles of controller.
The plunger travels from the bottom of the well to
the surface lubricator on the wellhead when the
force of the lifting gas energy below the plunger is
greater than the liquid load above the plunger.
Any gas that bypasses the plunger during the
lifting cycle flows up the production tubing and
sweeps the area to minimize liquid fallback.
The increments of the travel cycle are controlled
by a surface controller and may be repeated as
often as needed.
The Plunger Lift has several points of wear: the
plunger and associated seals, the downhole
bumper, and the surface pressure control
equipment including the wellhead and lubricator.
Additionally, the well may have to be worked over
due to tubing failure
Weatherford Plunger Lift System
Artificial Lift Installation – Plunger Lift
Reasons For
Workovers

23. Introduction to Workovers and Completions
23
Artificial Lift Installation – Gas Lift
Gas Lift
Installation
This system can be installed during the initial completion or
at a later time through a workover.
Failures of the system can be surface control equipment and
failed gas lift valves.
Surface equipment cab be repaired without downhole
intervention but repairing faulty gas lift valves requires
intervention by slickline, coiled tubing or a workover rig.
Halliburton Gas Lift Installation
Reasons For
Workovers

24. Introduction to Workovers and Completions
24
Producing Formation Basics
Reasons For
WorkoversFormation Damage
In order for a formation to produce commercial quantities of hydrocarbons several
things must be in place:
Obviously hydrocarbons must be present; the by-products of complex chemical
and physical changes. Organic debris accumulates in muds at the bottom of
marine environments (fresh and salt water). Deposition buries the organic material
and mud. In time and under the right conditions, hydrocarbons form and begin
their slow migration to the surface since they are lighter in density than the
surrounding formation waters. The muds further compress and form shales.
Hydrocarbons collect in porous rock formations that are overlain by non-porous
rock layers. Sandstones and carbonates (limestones) make up the bulk of
reservoir rocks.
Structural traps must be present – rock layers that allow hydrocarbons to
accumulate without escaping.
Rock characteristics: adequate porosity and permeability.

25. Introduction to Workovers and Completions
25
Pore Spaces
Porosity – Simply defined porosity is the spaces
between the sand grains. Typically porosity averages
between 25% - 35%. That is to say that roughly 25% to
35% of a given volume of rock is not rock but pore
spaces. It is in these spaces that hydrocarbons
accumulate.
Porosity

26. Introduction to Workovers and Completions
26
Flow
Permeability
Permeability can be defined as the ability of a
formation to allow fluid flow, or how well the
pores of the formation are connected.
Permeability is measured in units known as
Darcies.
Apparent, or relative permeability has to do with
the ability of a formation to allow various types
of fluids to flow through it. This is affected by
the nature of the fluid that “wets” the sand
grains.
A “water-wet” sand allows both oil and gas to
flow through it compared to an “oil wet” sand.

27. Introduction to Workovers and Completions
27
Anticline Trap
Oil and/or Gas
Traps

28. Introduction to Workovers and Completions
28
Traps Intrusive Tectonic Activity
Salt Dome
Oil
Oil
Salt Dome

29. Introduction to Workovers and Completions
29
Fault
Oil and/or Gas
Fault TrapTraps

30. Introduction to Workovers and Completions
30
Unconformity Trap
Traps
Oil & Gas

31. Introduction to Workovers and Completions
31
Folded and Faulted Trap
Traps

32. Introduction to Workovers and Completions
32
Cement Filtrate Invasion – solids
invasion while drilling
PIPE DOPE
Perforator Debris
Iron Sulfide Scale
Dirty Completion Fluid
Causes of Formation Damage

33. Introduction to Workovers and Completions
33
Causes of Formation Damage – While Drilling
FILTRATE INVASION
Filtrate invasion usually occurs while the well is drilled.
Drilling mud use to drill wells contains solids, drilled up solids
and commercially added solids. These solids are suspended in
the fluid while it is circulated. Formation invasion takes place
when the mud comes into contact with a porous and
permeable formation and the pressure in the hole at the depth
of the formation is greater than the naturally occurring
formation pressure. Excessive filtration invasion can reduce
the permeability of a formation and inhibit production.

34. Introduction to Workovers and Completions
34
CEMENT INVASION
In a similar fashion to drilling solids, cement can invade a formation when casing is cemented
into place. And like drilling solids, cement invasion can reduce formation permeability and
productivity potential.
Causes of Formation Damage – While Drilling

35. Introduction to Workovers and Completions
35
Causes of Formation Damage – While Completing or Working Over
PIPE DOPE
Other sources of formation damage occur during production, completions and workovers. The
worst damage is caused by pipe dope. Pipe dope, while necessary, is commonly used to
excess. This excess finds its way out of the workstring through fluid circulation and into
producing formations where it decreases permeability. Pipe dope, once deposited, is virtually
impossible to remove, so the damage is permanent.
PERFORATOR DEBRIS
When a perforator goes off it pushes various types of chemical and metallic debris into the
producing formation. This debris, if not flowed out of the formation, can remain and decrease
near-wellbore permeability. Because of this, some wells are perforated underbalanced to
initiate an immediate flow into the well following perforation.
DIRTY COMPLETION FLUID
The fluid of choice in most completions and workovers is a solids-free brine. Brines can be
mixed to supply sufficient density to control even the most extreme formation pressure –
Calcium Bromide/Zinc Bromide can be mixed to a stable density of 20.2 ppg. And this is
accomplished without solids, which can cause formation damage. It defies logic to use a
solids free fluid and then mix and store it in dirty pits and fail to filter it when it is circulated
through the well.
IRON SULFIDE SCALE
Iron sulfide, a compound created from the chemical combination of iron and sulfur, collects
on the inside of the tubing string and can be dislodged during trips into and out of the hole.
Naturally, this bulk of this debris remains in the well and is circulated around by the workover
fluid, but some does find its way into the producing formation and can reduce permeability.