Perforating Techniques

Agenda  What

is Perforating

 Perforating  Choosing

methods/ techniques

a perforating program

 Perforating

guns and functions

 Perforating

parameters

 Planning

a perforating job

 Perforating

clean up consideration 1

What Is Meant By the Term Perforation?  In

the context of oil and gas wells, a perforation is a hole punched in the casing or liner of the well, which allows the reservoir to connect with the wellbore in order to influence flow and allow hydrocarbon recovery.

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Why Perforate? Perforating a well is done in order:  To create

a channel between the pay zone and the wellbore.

 To allow

oil and gas to flow to the wellbore

easily.  For

future stimulation. example: Hydraulic fracturing 3

Perforation Techniques Perforation techniques/ strategies spans on a wide range and thus the method used primarily depends on the type of well completion.

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Completion Methods Basically there are two methods of completing a well, cased hole and open hole in which either can be natural, stimulated and sand control type completion method, each having different perforating requirements.

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Completion Methods  Stimulated

Completion Hydraulic fracturing and matrix acidizing – a small angle between shots are critical to effectively create hydraulic fractures and link perforations with new pathways to the reservoir

 Sand

Control Completion In gravel packing, many large diameter perforations effectively filled with gravel are used to keep the typically unconsolidated formation from producing sand and creating damage that would result in large pressure drops during production. 6

 Natural

completion In natural completion (in which perforating is followed directly by production) many deep shots are most effective.

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Basic Perforating Methods Cased holes may be perforated using several devices: 1.

Conventional casing guns which are run into the well on electric wire-line with or without wire-line pressure control equipment

2. Through-tubing guns which are run into the well after the tubing has been installed, again via wire-line pressure control equipment. 3. Tubing-conveyed guns which are run on the bottom of the tubing string and detonated using mechanical, electrical or pressureactivated firing mechanism 8

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 Perforating

can be done either overbalanced, with a higher pressure in the wellbore than in the formation, or underbalanced, with a wellbore pressure lower than formation pore pressure.

 Depending

on the option chosen and the degree of pressure differential, completion fluid will flow into the formation, or formation fluids will flow into the wellbore when perforations are created in a productive reservoir. 10

Considerations for Choosing a Perforating Program  The

relative importance of hole size, penetration, and shot density (shots per unit length)

 The

safety issues related to the particular well site conditions

 The

anticipated radial extent of formation damage due to drilling fluid losses

 The

reservoir's pressure, permeability, and susceptibility to damage from completion fluids 11

 The

length of the perforated interval, the size of the completion string components, and the need to perform specialized operations (e.g. sand control, stimulation)

 The

expected pressure, temperature, and timing extremes for the perforating operation

 The

relative economic importance of minimizing short‐ term costs versus maximizing long‐term productivity

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Types of Perforating Guns Optimizing perforating requires best selection of hardware best suited for the job. Types of guns:  Retrievable steel hollow carrier guns  Semi‐expendable wire or strip carrier guns  Fully‐expendable guns

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Fundamental of Shaped Charges Figure 2 (Shaped charge components) illustrates the relatively simple construction of the shaped charge.

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Shaped Charge

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Perforating using Shaped Charges

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Figure 3 Figure 2 21

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Temperature limitation of charges

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Functions of Perforating Guns

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Types of Perforating Guns  Retrievable

steel hollow carrier guns  Semi‐expendable wire or strip carrier guns  Fully‐expendable guns

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Retrievable Steel Hollow Carrier Guns

 With

the retrievable hollow carrier gun, the charges are positioned within a steel cylinder.

 Within

the carrier, each charge is surrounded by air at surface pressure, and is aligned with a threaded port plug or a thinner portion of the carrier wall (scallop gun).

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Upon detonation, the jet pierces the plug, providing a positive indication of firing when the gun is retrieved. The carrier cylinder may expand slightly due to the explosive force, but most of the debris is recovered within the gun. 29

 Other 1. 2. 3.

types of hollow carrier guns include:

Port plug gun High shot density gun The high efficiency gun system (HEGS)

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Advantages and Disadvantages of the Retrievable Steel Hollow Carrier Guns Advantages  High

reliability because all components are protected within the carrier (generally gas tight and chemical resistant)

 Generally  Very

higher temperature and pressure ratings

little debris left in well

 Explosive

force is retained within carrier to eliminate casing deformation 31

Disadvantages  May

have trouble running through tubing - retrievable guns in buckled tubing due to rigidity of carrier.

 May

have smaller charge components than comparable expendable guns, with some resulting reduction in penetration

 Weight

may limit length of assembly and, therefore, of perforation interval that can be shot with single gun run 32

Expendable Guns  Expendable

guns are designed to partially or completely disintegrate upon firing. They typically consist of a series of individually sealed charge cases constructed of a frangible material (aluminum, ceramic, glass, or cast iron).

 After

firing, only the wire line remains to be retrieved from the well.

 Semi‐expendable

guns are designed with a strip or wire carrier that is retrieved after firing. 33

Advantages and Disadvantages of Fully Expendable Guns

Advantages  Generally

cheaper and easier to assemble at the well

site  Lighter

and more flexible than steel hollow carrier guns, facilitating longer perforation intervals

 Size

for size, these offer more penetration than comparable retrievable guns (up to 25% increase for very small diameter guns) 34

Disadvantages Can 

deform casing when detonated

Leave substantial amounts of debris in well

Charge

cases may not be leak proof, allowing gas or liquid to enter casing and reduce performance

Guns

are not as sturdy (by design) as retrievable guns and premature breakage may result in fishing operations; running speed usually is limited to 168 ft/min

Pressure

and temperature limits usually are lower than those of retrievable

guns 35

Advantages and Disadvantages of Semi-Expendable Guns Advantages 

Same as fully expendable



Some reduction in amount of debris left in wellbore due to recovery of linkage system and carrier frame



With a metal strip or wire carrier, ceramic or glass charge cases can be used, reducing the size of debris particles and increasing resistance to chemicals and gas leakage 36

Disadvantages  Generally

the same as fully expendable, although ceramic casings are somewhat sturdier and wear resistant

 Debris

or a loose charge casing can cause gun to lodge in tubing while running in, causing further breakage and jamming; fishing can be difficult and may require that the tubing be pulled or casing drilled out 37

Gun System Exposed Guns Hollow Carrier Guns

Strip Pivot Scallop Port plug High efficiency High shot density

Wireline throughtubing x x x  

Application Wireline throughcasing       x

x

x

 

x

x

x

Tubing conveyed        

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Casing Guns Both retrievable and expendable guns are used. (Retrievable hollow carrier guns normally range from 3 1/8’’ up to 5”. Expendable and semi-expendable casing guns are generally available in sizes from 3 1/8” to 4”)  Due to small clearance, the guns do not require positioning against the casing.  Phasing can be employed to minimize geometrical skin effects during flow.  Any shot density can be employed to minimize geometric effects. 

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Through Tubing Guns  Smaller

diameter than casing guns.  Often equipped with positioning devices (magnetic or mechanical) to set the gun against the casing.  Charges are often positioned for “in-line firing” (zero degrees phasing).  Well can be flow immediately after perforating. 40

Calculating Mud weight for Overbalance perforating  Overbalance

= Hydrostatic – Formation

pressure  Estimate reservoir pressure  Use the following equation to determine the weight of fluid required to obtain the overbalance: P  0.052 * MW * TVD

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Calculating Mud weight for Underbalance perforating  Underbalance

= Formation Pressure -

Hydrostatic  Estimate reservoir pressure  Use the following equation to determine the weight of fluid required to obtain the underbalance: P  0.052 * MW * TVD

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Perforating Techniques 43

Perforating Techniques 1. 2. 3. 4. 5. 6. 7. 8.

Through-Tubing wire line perforating technique Tubing-Conveyed perforating technique Positive-Pressure/ Reverse surge technique Perforating for gravel packing Perforating for fracturing Highly overbalance perforating Electric wire line perforating Positioned or oriented perforating 44

Through-Tubing wire line Perforating Technique

 The

tubing and packer are run and set in the well.  Pressure control equipment is installed and tested.  A differential pressure is obtained by circulating fluids into the tubing  The gun assembly is then run into the tubing on small‐diameter cable (0.18 to 0.22 in.)  After firing, the well is typically flowed for 15 to 30 minutes before the gun is recovered

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Tubing-Conveyed Perforating (TCP) Technique

 A large‐diameter

casing gun is run into the well on a tubing string that includes a packer  Since a large‐diameter gun is used, gun phasing can be designed to reduce "skin" (90º to 120º)  The tubing may be run dry or partially filled with a fluid cushion to establish the proper level of underbalanced pressure.  A packer is then set. 46

 After

positioning, a vent is opened to equalize the pressure below the packer with the tubing.  One of a variety of firing devices may be used to detonate the charges, after which flow is established through the vent.  The gun may be dropped into the rat-hole. This technique also permits the perforating of long intervals in highly deviated wells 47

Compared to through‐tubing perforating, we can say that tubing‐conveyed perforating (TCP):  Allows

greater penetration and multi-phasing  Permits a greater degree of underbalanced pressure without risk of blowing the gun up in the hole  Demands operational rig time equal to or less than wire line perforating, particularly in deviated holes with long pay intervals  Generally costs about 25% more than wire line perforating (without accounting for possible time savings) 48

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Positive-Pressure/ Reverse Surge Technique

 (PACT or

Positive Action Completion Technique) involves first perforating the well under conventional overbalance conditions using large‐diameter casing guns.

 The

tubing and packer are then run into the hole with some type of shear‐disc assembly included in the tubing string.  With the disc, the tubing may be run dry or with a water cushion  Using a drop bar or casing pressure ‐operated mechanism, the disc is sheared, exposing the perforation to a sudden drawdown or "surge.“  A tubing plug may be run immediately above the disc and recovered using a slick-line once the packer has been set 50

Perforating for Gravel Packing

In an ideal gravel‐packed completion, the perforation tunnel is filled with a clean, evenly sorted, high permeability sand or "gravel."  Gravel‐pack completions are typically shot with large hole diameters (0.6 to 0.8 in.) and high densities (8 to 12 SPF).  Perforator size may also be limited by packer bore diameter in cases where guns are run on tubing. 

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Perforating for Fracturing Perforation parameters  Casing entrance hole size – 0.375 to 0.5” 

Effective shot density - Shot density requirements are based on maintaining reasonably low breakdown, treating and initial shut‐in pressures. Typical treatments employ 4‐8 shots per foot.

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 Gun

phasing - it is important to minimize the angle between the perforations and the plane normal to the minimum far‐field stress. For typical fracture treatments, a phasing of 20 o to 60o is recommended.  Character of perforations in the formation - An intermediate penetration of about 4 to 6 inches is generally adequate 53

Highly Overbalance Perforating The pressures applied to the perforations are equal to or greater than formation fracture pressure, represents an alternative to conventional techniques. Advantages  Stabilization of the tunnel walls resulting from prolonged application of high pressure.  The initiation of fractures at the tips of the perforations. 54

Before perforating, pressure is applied to the wellbore using an all‐gas, all‐liquid or combination gas-liquid fluid column.  The highest bottomhole pressure will be attainable through tubing‐conveyed perforating assemblies.  If the overbalance is high enough, the rate of fluid displacement will exceed the capacity of the perforations to accept fluid.  Additional fluid can be pumped into the formation to enhance breakdown. 

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Electric wire line Perforating The primary components of the system are:  The

perforating tools (gun cable head, collar locator, weights)  The cable  The sheave and tension indication apparatus  The logging truck (including cable winch and control panels)  The pressure control system 56

The perforating guns are run into the hole along with a device for detecting the position of each casing collar.  The casing collar locator is a simple magnetic device that responds to the increase in metallic mass associated with a casing collar coupling. 



Such weights may have an electrical conductor built into them to transfer firing power to the guns 57

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Positioned or Oriented Perforating Oriented perforating may be undertaken for two reasons:  Perforating the upper zone through tubing in a multiple completion (between packer perforating)  Perforating a single string in a multiple tubingless completion

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Reason 1 

As the gun passes alongside the adjacent tubing string, the arm ensures that the gun is positioned at an angle away from the tubing.



A switch within the tool gives an indication at the surface that the gun is facing correctly.



A retrievable hollow carrier gun is used to prevent damage to the adjacent tubing and to prevent debris from settling inside the casing on top of the lower packer. 60

A mechanical orienting tool is often used. 61

Reason 2  A motorized

orienting tool is used.  This tool uses a focused source of gamma rays and a focused detector to measure the density of the material between them.  When displayed on coordinate plot, the correct compass direction for firing is determined.

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Perforation Productivity Consideration In a perforated completion there are basically four geometrical parameters that affect productivity.  Shot

density (SPF or number of flowing perforations per unit length)

 Perforation

depth (penetration into formation)

 Gun

phasing (angular displacement between adjacent perforations)

 Perforation

diameter (within the formation). 64

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Perforation Parameters Perforating parameters include - shot density, penetration, hole size, and phasing These parameters depends on the type of formation, the expected productivity, and the degree of damage.  High

shot density-anisotropic or laminated reservoirs  Penetration becomes more important than shot density the farther that drilling damage extends into the formation. 66

Some type of angular phasing is important when high rates are expected and, in general, phasing will improve productivity by 10 to 20%, although the angle (90º, 120º, 180º) is not critical.  Hole size is relatively unimportant beyond a minimum diameter of about 0.25 in. unless the well must be gravel packed or fractured, in which case hole size becomes critical 

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Planning a Perforating Job The first step in planning a perforating job is to accumulate the necessary data. Casing and/or liner size and weight, tubing size and weight  All tubing restrictions, their ID and location  The type of packer and the pressure it can withstand without unsealing 

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 The

specifications of the wellhead or blowout preventer connection, flange and type  Pressure test specifications for tubing, casing, and wellhead equipment  The condition of the casing or tubing, excessive wear, crooked tubing, corrosion

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Other well conditions that must be specified or estimated include:  The

expected bottom-hole temperature  The type of fluid in the wellbore and in the formation  The fluid level in the tubing or casing  Pressure and rate specifications of surface facilities if well is to be flowed  Anticipated H2S concentration, if any 

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When choosing a perforating company, consider the following points:  Record

of service in the area  Experience and training of operators  Equipment quality  Testing, certification, and maintenance procedures  Thorough and accurate record keeping  Accurate depth control procedures 71

Perforating Cleanup Consideration According to Bell (1982), the factors influencing the number of clean, open perforations are:  Type

of formation  Quality of the charge  Type of completion fluid  Flow time for cleanup  Level and direction of differential pressure 72

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Conclusion  Oil

and gas well can be perforated via many techniques with the use of several different types of perforating hardware (guns).

 It

is important to choose the correct perforating strategy for each individual well, as each well is distinct with varying characteristics.



Perforating a well, will allow production, and can also provide future work such as simulation. 75