PE-103
Applied Completions and Workover
Perforating
Module 7
Course Contents
Introduction: Definitions and Objectives
2. Reservoir and Mechanical Considerations in Well Completion Design
3. Well Completion Design: Types and Applications
4. Tubing Design
5. Subsurface Production and Control Equipment
6. Completion and Workover Fluids
7. Perforating
8. Sand Control
9. Stimulation
10. Remedial Cementing
1.
Perforating
3
Module 7: Perforating
7.1 Creating a Perforation
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Objective
Types of perforators
The shaped charge
Perforation clean-up
7.2 Well Conditions Which Influence Perforating System
7.3 Optimizing the Type of Perforating Gun
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Gun Types
Perforating Mode
7.4 Optimizing the Charge Performance
Perforating
4
7.1 Creating a Perforation
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Objective:
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To establish effective flow communication between the wellbore and
the formation
Achieving good well productivity (or injectivity) involves:
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
Perforating
Selecting appropriate perforating equipment & techniques
Establishing conditions in the well at the time of perforating conductive
to good perforation cleanup or flow response (e.g. fluid type &
differential pressure)
5
7.1 Creating a Perforation
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Types of perforators
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Bullet perforators
Hydraulic perforators
Mechanical cutters
Shaped charge perforators
Most perforating is done with shaped charge perforator
Perforating
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The Shaped Charge
Perforating
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The Shaped Charge
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Components:
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Case: Made of steel or aluminum or ceramic
Liner:
• Made of particulate
alloy metal (copper + lead + tungsten)
• Turns into powder after explosion
• Optimum angle = 42o

(affects perforation length & diameter)
Explosive:
• Commonly cyclonite
(RDX) [OT < 340oF]
• Rapid detonation causing pressure on liner of several 106 psi

Detonating Cord:
• Carries a charge of 5 gm/ft
Perforating
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Jet Penetration Mechanism
Perforating
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The New Perforation
Perforating
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The New Perforation
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Compacted zone:
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Crushed formation rock
K = 1/5 to 1/20 Koriginal
Debris:
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Perforating
Pulverized formation material
Pulverized cement
Particulate matter from liner hydraulic perforators
11
Perforation Clean-up
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Flowing the well:
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Injecting fluid (perforation breakdown)
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Fluid drag forces act on compacted zone & debris
Usually inadequate
Brine, KCL water, acetic acid, HCL, & HF
Compatibility with formation is important
Perforating underbalanced

Perforating
Reverse differential pressure perforating
12
Recommended Range of DP
•
Perforating
Formation K
Liquid
Gas
> 100 MD
200 – 500 psi
1000 – 2000 psi
< 100 MD
1000 – 2000 psi
2000 – 5000 psi
High P → Surge → removes debris & improves permeability
(K) of compacted zone
13
Core Flow Efficiency (CFE)
Differential Pressure vs. Perf. Flow Efficiency
Reverse Differential Pressure (psi)
Perforating
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Core Flow Efficiency (CFE)
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A measure of perforation clean-up as observed in laboratory tests:
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CFE Range: 0.70 to 0.85
Perforating
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Perforation Clean-up
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Factors influencing perforation clean-up
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Perforating
Type of formation
Quality of charge
Differential pressure level & direction
Type of completion fluid
Amount of time flowed
16
Factors Influencing Perforation Clean-up
Perforating
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7.2 Well Conditions

Diameter of tubular goods:
Tubing OD, in.
2 3/8
2 7/8
4 1/2
5 1/2
Max. Gun OD** in.
1 11/16
2 1/8
3 5/8
4
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Perforating
** After detonation OD
Check min. ID of tubing using a gauge ring
Use a "dummy gun" for deviated wells before running perforation gun
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7.2 Well Conditions
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Length of the interval(s)
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Perforating
Determine length of gun, spacing for blank lengths, number of trips, etc.
Well Fluid
DP Required to initiate flow
Condition of perf. after flowing
10 lb Brine
0 psi
Clean, or partially filled with
mud & debris
10 lb Mud
30 psi
Partially or completely filled
with mud & debris
16 lb Mud
100 psi
Completely filled with mud,
sand, & debris
It is recommended that perforation fluid be clean, solid-free & non-damaging
to formation
19
7.2 Well Conditions

Formation Temperature
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Static Formation Temperature
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The integrity of perforation explosives is temperature/time dependent
High formation temperature requires special explosives & detonating
electronics (now available for up to 600oF)
Time
Perforating
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7.2 Well Conditions
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Formation Pressure
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Important for:
• Making DP calculations
• Pressure rating of lubricator
• Pressure rating of perforation gun

Pressure rating of guns: 7000 to 20000 psi depending on type of gun
Perforating
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7.2 Well Conditions
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Casing grade
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Perforation diameter decreases with increasing yield strength
Service companies report perforating diameter data based upon standard
test (API RP-43, Sec. I), using J-55 steel
To estimate perforating diameter 'd' from reported diameter 'dr'
d = dr Sr / S
• Where, Sr = reference yield strength (55000 psi)
S = yield strength of casing in the well
Perforating
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7.2 Well Conditions
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Formation compressive strength
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Affect penetration (should extend through casing, cement, damaged
near-wellbore area, and into virgin reservoir rock)
Wellbore geometry
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Conventional completion with TBG out of the hole allows large OD gun for deep
penetration but limits reverse DP, well testing, and stimulation operations

Tubingless completion and conventional completion with TBG in, limits the OD of gun;
multiple tubingless or conventional completion requires orienting device

For conventional multiple completion we may set a plug in the lower packer, pull both
strings, then perforate the upper zone
Perforating
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7.2 Well Conditions
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Hole washouts
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When hole gets larger than bit size (say by 5 to 10 in.), large gun is needed to
penetrate through the additional cement
Check the caliper log of the well
Planned stimulation treatments

Perforating
Affect size and number of perforation required
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7.3 Optimizing the Type of Perforation Gun
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Gun types:
(1) Hollow steel carrier
• Through-tubing:
•
D = 1 3/8" – 2 7/8"
•
Scalloped → increases
penetration & contains the
carrier burr
• Casing guns:
•
Perforating
D = 2 7/8" - 6"
25
Hollow Steel Carrier Guns
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Advantages:
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Perforating
Higher reliability
Higher mechanical strength
Higher temperature & pressure
Capacity or ratings 340 – 350 OF @ 15000 – 20000 psi
Some special carriers are rated at 600 OF & 25000 psi
Min. debris left in the wellbore
Can be directionally oriented
Can be run in the hole at high speed
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Hollow Steel Carrier Guns
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Advantages (cont.):
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Perforating
Not affected by wellbore fluids
Easily adaptable to desired shot density and perforation patterns
Relatively easy to pass through tight spots and will not separate due to its
rigidity and strength
Casing is not deformed because the carrier shell absorbs most of the energy
shock from the charge detonation
Selective firing is allowed
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Hollow Steel Carrier Guns
 Disadvantages:
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
Perforating
Its rigidity may cause problems when attempting to pass gun through
a deviated section of pipe
Multiple trips using short lengths of gun may require higher
mechanical strength
Higher cost
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7.3 Optimizing the Type of Perforation Gun
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Gun types:
(2) Fully-expendable guns
Perforating
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Fully-Expendable Guns
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Advantages:
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Perforating
Less expensive than hollow steel carrier (HSC)
Provide deeper penetration by a factor of 1.1 to 1.3
Flexibility permits use in deviated tubulars (bending radius about 5 ft)
Can be easily assembled at well site
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Fully-Expendable Guns
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Disadvantages:
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Perforating
May cause CSG damage
Less reliable than HSC – explosive components exposed to
wellbore environment
Debris is left in the well, may bridge in TBG or choke
Cases are made of aluminum (which is acid soluble and prone to gas
leakage); this adversely affects charge performance
Lower pressure & temperature ratings than HSC
Impossible to determine if all charges have been fired
Not reliable in select-fire applications
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7.3 Optimizing the Type of Perforation Gun
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Gun types:
(3) Semi-expendable guns
Perforating
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Semi-Expendable Guns
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Advantages:
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
Perforating
Volume of debris is less than for (F.E.)
Use ceramic or steel cases → debris is less chunky and does not have the
bridging tendency of aluminum
Ceramic cases are gas-proof and acid-resistant; provide deeper penetration
by a factor of 1.1 to 1.3
33
Semi-Expandable Guns
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Disadvantages:

May cause CSG damage
Less reliable than HSC – explosive components exposed to wellbore
environment
Debris is left in the well, may bridge in TBG or choke
Cases are made of aluminum (which is acid soluble and prone to gas leakage);
this adversely affects charge performance
Lower pressure & temperature ratings than HSC
Impossible to determine if all charges have been fired
Not reliable in select – fire applications
Perforating
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7.3 Optimizing the Type of Perforation Gun
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Gun types:
(4) Tubing – Casing Puncher
• Limited-penetration
gun
• Can perforate TBG without perforating CSG
• Used to establish circulation
• Similar to scalloped gun in shape
Perforating
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Perforating Mode
(1) Through Casing:
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Perforating
Can use large diameter HSC casing guns
Larger shaped charges → wider & deeper perforations
Best for large washouts, sand control & hydraulic fracturing
Normally used under overbalanced conditions (well control is difficult
without tubing in the hole)
Perforations clean-up requires either fluid production or fluid injection
36
Perforating Mode
(2) Through Tubing:
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Most common
Used when:
• Well control requires tubing
in the hole
• High DP is required for clean-up
• Cost of pulling
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Perforating
tubing is high
Provide cleaner perforations
Narrower & shorter perforations
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Perforating Mode
(3) Tubing Conveyed Gun
Surge Tool
Perforating
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Perforating Mode
(3) Tubing Conveyed:
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Combines the advantages of through-tubing, and casing guns (deep and wide
holes with high DP)
Advantages:
• Maximum formation energy can be used for clean-up
• No hazard of gun blowing
up the hole
• Minimum formation contact with completion
fluids
• Larger perforating capacity of CSG gun
• Does not require
Perforating
a lubricator
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Perforating Mode
(3) Tubing Conveyed:

Disadvantages:
• Only way to confirm
that all charges have fired is by pulling TBG & gun
• Detonation bar may not go through in deviated holes or debris filled holes
• Gun assembly in the hole may hinder future workover operations
• High cost (about 40% higher than through TBG)
Perforating
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7.4 Optimizing the Charge Performance
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To optimize the charge performance for a particular operation, the
following factors must be considered:
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Perforating
Perforation depth
Shot density
Clearance
Perforation diameter
Gun phasing and clearance
41
7.4 Optimizing the Charge Performance
(1) Perforation depth:

To maximize well productivity, perforations should penetrate beyond the zone
of drilling mud filtrate invasion
Perforating
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7.4 Optimizing the Charge Performance
(2) Shot density:
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
Perforating
For wells without sand control problems, used 2 to 4 SPF or more
For wells with sand problems, use 8 to 12 SPF; this reduces DP across
perforations → reduces drag forces on sand grains
Wells scheduled for limited entry treatment should have low shot density
(1 SPF to 1 shot / 10 ft.)
43
Shot Density
Perforating
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Shot Density
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High shot density perforating has the following disadvantages:
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Perforating
Makes diversion of treating fluids difficult
Makes squeeze cementing operation difficult
High cost
45
7.4 Optimizing the Charge Performance
(3) Clearance
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Perforating
Centralizing when using a CASING GUN is practical → same depth & diameter
for all perforations
Centralizing not recommended with through tubing guns
Decentralization with 0o phasing is used when limited entry stimulation is
planned since hole size is critical
46
7.4 Optimizing the Charge Performance
(3) Clearance
Perforating
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7.4 Optimizing the Charge Performance


Perforating diameter does not
have any significant effect on well
productivity
It is important in sand control &
limited entry diversion operations
Productivity Ratio
(4) Perforation diameter
Perforation Diameter (Inches)
Perforating
48
7.4 Optimizing the Charge Performance
(4) Perforation Diameter
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
Perforating
For gravel packing operations, large size perforations should be used
(min. 0.5 in.)
Limited entry diversion is a process where a sufficient amount of differential
pressure is established across the perforations to equally proportion the
treatment among all of the holes
49
7.4 Optimizing the Charge Performance
(4) Perforation Diameter

To determine the perforation diameter (D) required to provide a given DP:

Where, Q = injected fluid rate (BPM / perf.)
C = perforation coefficient (0.95)
DP = desired pressure drop (psi)
ρ = fluid density (ppg)
Perforating
50
Optimizing the Charge Performance


Phasing is the horizontal angle
between consecutive perforations
(0o, 60o, 90o, 120o, & 180o)
Phase angle does not significantly
affect the productivity ratio
Productivity Ratio
(5) Phasing
Phase Angle
Perforating
51