Perforation

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Suez Canal University Faculty of Petroleum & Mining Engineering Petroleum Engineering Department

2008/2009

Perforation

Made by: 1-Ahmed Gamal Abd El-Aziz 2-Ahmed Magdy Abd El-Kareem

Presented to:

3-Farid Abd El-Salam Gad 4-Mohamed Ahmed Shawky

Prof.Dr / Ahmed El-Gebaly

5-Mohamed Borhan Bakeer

Perforation

Contents : 1.

Well completion 1.1. Well completion & skin effect 1.2. Types of well completion

2. Perforation 2.1. Overview 2.2. History of Perforation in Brief 2.3. Gun systems 2.3.1.Overview 2.3.2 Types of perforating guns 2.3.3. Factors affecting the perforating gun performance 2.3.4. gun components 2.3.4.1. Shaped charge liner 2.3.4.1.1. SHAPED CHARGE THEORY 2.3.4.1.2. SHAPED CHARGE DESIGN 2.3.4.2. Detonator 2.3.4.3. The S.A.F.E system 2.3.4.4. Key components of the safe system 2.3.4.5. Operation mechanism of the S.A.F.E SYSTEM 2.3.4.6.Secure Detonator 2.3.5. Casing guns 2.3.6. Parameters of gun selection 2.3.7. High shot density guns 2.3.8. Through-tubing Guns 2.4. Explosives Classifications Page 2

Perforation

2.4.1. Low explosives (propellants) 2.4.2. High explosives 2.4.2.1. Primary high explosives 2.4.2.2. Secondary high explosives 2.4.3. Effect of temperature 2.5. Types of perforation techniques 2.5.1. According to the relation between reservoir and hydrostatic pressures 2.5.1.1.

2.5.1.2.

underbalanced perforation overbalanced perforation

2.5.2. According to where we do perforation 2.5.2.1. Shop perforated casing are classified to 2.5.2.2. Gun perforated casing: Optimum perforation 2.5.2. According to how we do perforation 2.5.2.1 WIRELINE CASING GUN TECHNIQUES 2.5.2.2. THROUGH-TUBING PERFORATING TECHNIQUE 2.5.2.3. TUBING-CONVEYED PERFORATING TECHNIQUE 2.5.2.3.1. TCP firing systems 2.5.2.3.2. Percussion-Activated Firing Head 2.5.2.3.3. Bar Actuated Pressure Firing System 2.5.2.3.4. Differential-Pressure Firing Head 2.5.2.3.5. Tubing - Pressure Firing System 2.5.2.3.6. Electric - Wire line Firing System 2.5.2.3.7.job planning and operational considerations for TCP 2.5.2.3.7.1. Radioactive Marker Sub 2.5.2.3.7.2.Cone-Type Debris circulating Sub Page 3

Perforation

2.5.2.3.7.3. Mechanical Gun Release Sub 2.5.2.3.7.4. Surge-Disc Sub 2.5.2.4. COILED TUBING CONVEYED PERFORATING FOR HORIZONTAL WELLS 2.5.2.4.1. Principle 2.5.2.4.2. Procedure 2.6. depth control 2.6.1. WIRELINE DEPTH CONTROL 2.6.1.1. Gun-Gamma Ray Tool 2.6.1.2.Precision Identified Perforations 2.6.2.TCP DEPTH CONTROL 2.7. GENERAL SAFETY PROCEDURES 2.7.1. Firing Systems for TCP Operations 2.7.2.Tubing Pressure Activated 2.7.3.Mechanical Impact 2.7.4.Electrically Activated 2.7.5.Retrievable Slick line Firing Head Safety

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Perforation

1.Well completion Do you think a well is ready for production as soon as it's drilled? Well completion is the phase that comes after the drilling of a well but before the well is used for production. The process of well completion involves a group of operation that extends beyond simply installing well bore tubular & well completion equipment. In fact the well completion process includes: 1- installing & cementing 2- running production tubing 3- Perforating a well 4- cleaning up or testing Occasionally the completion design can be affected by factors such as a complex wellhead or any processing storage requirements affecting productivity. Completion engineers used 2 main industrial terminologies: 1- lower completion for the part across reservoir sand face that includes perforation, flow control valves & permanent monitoring 2- Upper completion for part above packers' assembly that includes safety valves, gas lift mandrels, tubing & wellheads. Photo There are 3 basic requirements that any well completion must meet. A well completion system must be 1- efficient in terms of meeting all the production objectives 2- safe in terms of a secure well environment 3- economic in terms of the profit generated over the cost incurred Based on the completion objectives, well completion is divided into 3 basic styles. These are 1- temporary 2- permanent 3- workover

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Perforation The table below displays the difference between the different styles of well completions

Well completion:' its significance in productivity' The significance of well completion lies in the fact that it is the only productivity factor, amongst three, which can be influenced by man to increase productivity. The two other productivity factors namely Reservoir Boundary & Reservoir properties are natural factors over which man has no control.

1.1. Well completion & skin effect While designing well completion factor that must be taken into

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Perforation consideration is the skin effect. Skin has a direct impact on well productivity which can be +ve or –ve. Skin is the change in radial flow geometry near the well bore caused by flow convergance, wellbore damage, perforation, partial penetration and deviation. The effect of skin can be seen as a pressure drop across the completion this drop in pressure results from reduction in total pressure available to bring fluids from a distance Re to the well bore at distance Rw.the pressure at distance Re from the well bore axis is the undisturbed reservoir pressure.Pewhrer as the pressure at a distance Rwfrom the well bore axis is the well bore pressure Pwf.the resultant pressure drop is the draw down that causes movement of fluids from a distance Re to the distance Rw There are different ways to maximize the productivity. These include: 1- creating highly conductive path to the well bore by fracturing the formation 2- reducing the viscosity by employing methods such as steam injection 3- removing skin by employing methods such as acidizing 4- increasing well penetration by perforating deeper into the formation 5- reducing formation volume factor by choosing correct surface separator

1.2. Types of well completion: 1- open hole completion 2- cased hole completion "in which we use perforation" 3- slotted linear completion 4- gravel back completion

2. Perforation 2.1. Overview Perforating is a critical part of any well completion process. The perforating process generates holes -perforation tunnels- in steel casing surrounding cement and the formation. In the past, perforation was regarded simply

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Perforation as holes in steel casing made . By different methods. But perforation is not just a simple hole drilling process. Perforated completions play a crucial role in economic oil and gas production. Long term well productivity and efficient hydrocarbon recovery.

2.2. History of Perforation in Brief 1. Prior to the early 1930's, casing could be perforated in place by mechanical perforators. These tools consisted of either a single blade or wheel-type knife which could be opened at the desired level to cut vertical slots in the casing. 2. Bullet perforating equipment was developed in the early 1930's and has been in continuous and widespread use since that time. -The major drawbacks with this method were that the bullet remained in the perforation tunnel, penetration was not very good, and some casings could not be perforated effectively. 3. After World War II the Monroe, or shaped – charge, principle was adapted to oil well work, and the resulting practice is now commonly referred to as jet perforating. -The principle of the shaped charge was developed during World War II fo armor piercing shells used in bazookas to destroy tanks. This new technology allowed the oil producers to have some control over the perforating design (penetration and entry hole size) to optimize productivity.

2.3. Gun systems 2.3.1. Overview In order to allow oil and gas to flow into the well, conduits need to be made into the formation. To do this, a gun is positioned across the

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Perforation producing formation and is detonated to create perforations through the casing and cement. The guns used for this purpose are known as perforating guns.

2.3.2. Perforating guns are divided into two primary categories:  Capsule guns  Carrier guns

2.3.3. The perforating gun performance is affected by the       

Gun size Clearance Entrance hole diameter Shot density Gun phasing Perforating length Temperature rating

After firing the gun and while retrieving, unwanted solids enter into the wellbore or formation through perforating tunnels. These are called the perforating debris. Perforating debris can create problems in highly deviated or horizontal wellbores and can also create problems with the completion hardware. Sources of debris are not only gun system, but also from the casing, cement and formation. Gun hardware contributing to debris are:    

Gun body Shaped charge liner slug and jet Shaped charge case Shaped charge retaining system (that holds the charge inside the gun). Page 9

Perforation

2.3.4.1. Shaped charge liner Perforating debris sources can be controlled if properly engineered. Shape charge liner used in deep penetrating charges is made of powder metal, which eliminates the carrot and slug associated with liner penetration into the formation during charge detonation. Big hole charges us solid liners in order to produce large hole into the casing. However pf4621 power flow liners, produce big holes and yet leave no slugs into perforating tunnels, this new technology charge can replace the ultrapack charges. Attempts are made to contain the debris in the gun, collect it after perforating or minimize the quantity expelled. To address this problem of controlling the debris, two methods are used. These are:  Zinc casing method  Patented packing method Additional techniques that contribute to reduced perforating debris include powder metal liners and non-plastic charge retention systems. These recent innovations help in limiting problems arising from perforation debris.

2.3.4.1.1. SHAPED CHARGE THEORY The ultimate goal of perforating is to provide adequate productivity. Test laboratories evolved over the years to provide means of predicting and improving well performance. Today, the performance of the charges is determined according to the procedures outlined in the API RP 43 (standard procedure for evaluation of well perforators) fifth edition, published in 1991. From Figure B1 it can be seen that the penetrating power of a cylinder of explosive is greatly increased by a cavity at the end opposite to the detonator. Furthermore, placing a thin metallic liner in the cavity increases penetration. A typical shaped charge consists of four main components: a case, a high order explosive powder, primer and a liner, as shown in Figure shown

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Perforation

The case simply holds all the components together. - The explosive (RDX, HMX and HNS) is a complex mixture designed to allow packing and shipping in the case. - The primer is a purer mixture of explosive which is more sensitive to the detonation of the detonating cord. - The liner is used to form a jet which physically does the perforating. - The detonating cord, which is initiated by a blasting cap, detonates each charge.The selection of explosive material is based on the well temperature and anticipated exposure time at that temperature (Figure B3). RDX, HMX and HNS are all explosives used in oil well shaped charge manufacture. For deep penetrating charges, the liner is made from a mixture of powdered metals pressed into the shape of a cone. High precision in the pressing operation is required and it must be done in an extremely uniform and predictable manner. For Big Hole charges, the liner is drawn from a solid sheet of metal into hemispherical, parabolic, or more complex shapes. Page 11

Perforation For each of the two types of charges, there is a trade-off between entrance hole size and penetration. The sequence of events in firing is illustrated in Figure B4 from top to bottom. The detonator initiates the cord which detonates at a rate of approximately 7000 m/s (23,000 ft/sec.) The pressure impulse from this detonation initiates the primer in the charge and the explosive begins to detonate along the length of the charge. The high pressure wave 30x106 kPa, 4,500,000 psi) strikes the liner and propels it inward. The liner collapses from apex to skirt imparting momentum with a velocity approaching 2500 m/s (8000 ft/sec). At the point of impact on the axis the pressure increases to approximately 50x106 kPa (7,000,000 psi) and from this high pressure region, a small amount of material is propelled out at velocities in excess of 7000 m/sec (23,000 ft/sec). As the liner collapses further down the cone, more and more material must be propelled by less and less explosive such that the impact pressure is substantially less. Thus the tip of this so-called jet is travelling 20 times faster than the rear portion and gives the elongated shape to the jet. The penetration depth depends on this stretching action. As the liner walls collapse inward, the resultant collision along the axis divides the flow into two parts, as in Figure B5. The inner surface of the liner material forms the penetrating jet which is squirted out along the charge. The outer surface of the liner, which was in contact with the explosive, forms a rear jet or slug which moves forward slower than the forward jet. In the zone of collision, where division of the material forming the jet and slug takes place, there is a neutral point which moves along the axis as the liner collapse process continues. The very fast jet impacting a casing generates a pressure of approximately 70x106 kPa (10,000,000 psi). At this pressure the steel casing flows plastically and the entrance hole is formed.

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Perforation

A similar behavior occurs with formation material as the jet penetrates. In addition, crushing and compacting of the formation material around the perforation may also occur. The entire process from detonation to perforation completion takes from 100 to 300 microseconds. The jet material arriving last at the target, making the end of the perforation, comes from the skirt or base. As discrete portions of the jet strike at this end of the hole, they penetrate, expending their energy in the process. Portions of the jet continue the penetration process, until the entire jet is expended. The perforation occurs so fast that, essentially, no heat is transferred. Indeed, it has been demonstrated that a stack of telephone directories can be penetrated without singeing a single page. It follows that no fusing of formation material occurs during penetration. However, crushing and compacting of formation material is to be expected, and will be reviewed later.

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Perforation

2.3.4.1.2. DESIGN

SHAPED

CHARGE

Liner aspects, such as geometry, angle, material, and distance from base to apex, as well as stand off, and explosive density are more important than the amount of explosive (Figure B7a). Only about 20% of the available explosive energy goes into the useful jet. It has been proven that properly designed charges can out perform poorly designed charges that have twice the explosive load. This is important in situations where a higher explosive load causes casing damage. Once a charge is designed for entrance hole and penetration efficiency, manufacturing quality control and consistency become significant in shaped charge performance. Perforation efficiency is accomplished with maximum penetration, uniform crushed zone, and minimal plugging due to slug debris. This is achieved by designing a liner that will provide a uniform jet diameter and velocity with little to no deviation from the conical liner axis. For example, it is critical that the liner thickness and density be precise around the cone at any given point away from the apex. Figure B7b is an example of a less desirable jet due to poor quality control Page 14

Perforation

2.3.4.2. Detonators Perforating guns carry explosive charges to the borehole where they are detonated creating cylindrical holes in the casing and the cement. This allows oil and gas to flow from the formation into the well.

The critical parts of the perforating guns are:  Detonating cord  Detonators Detonators are divided into two main types:  Electrical detonators  Percussion detonators Electrical detonators are known as blasting caps and are typically used in wireline operations. Percussion detonators are generally used with tubing conveyed, coil tubing conveyedd and nonelectric wireline systems

2.3.4.3. The S.A.F.E system There are numerous safeguards implemented in both the electrical and percussion detonation systems. However, these conventional systems may explode accidentally when exposed to electric magnetic fields or other voltages found around the field. The S.A.F.E. Slapper-Actuated Firing Equipment system was developed to be immune from the potential differences created by the radioPage 15

Perforation frequency(RF) radiation, impressed current from corrosion cathodic protection, electric welding, high-tension power lines and induction motors such as top drives on drilling rigs. S.A.F.E. equipment is available for most types of perforating / explosive assemblies run on wireline .

2.3.4.4. Key components of the safe system The S.A.F.E. system initiates a gun firing without the use of any primary detonating material. The key components of the S.A.F.E. System are the EFI or exploding foil initiator and the ESIC or the electrical secondary explosive initiating cartridge. The ESIC generates a unique signature of high voltage and current and rapidly discharges the pulse. The pulse is necessary to fire the EFI.

2.3.4.5.Operation mechanism of the S.A.F.E SYSTEM Let's now look at the detailed operation mechanism of the S.A.F.E system. Here we see an internal view of the EFI with the components identified

2.3.4.6.Secure Detonator The secure detonator is a third-generation on S.A.F.E type device that Page 16

Perforation also uses an EFI. it does not contain primary high explosives or a downhole electronic cartridge. A microcircuit performs the same function as the electronic cartridge and EFI together in a package. It is similar in size to a conventional electric detonator. The secure system has all the technical advantage of S.A.F.E detonator, but is more reliable and fully expandable. It is also smaller in size and therefore allows the gun strings to be shorter. Both secure and safe system fire using high voltage and current. Their electronic circuits are protected and they don't fire accidentally in case of malfunction.

2.3.5. Casing guns Casing guns are a type of carriers. Traditionally, casing guns were run on wireline to perforate wells before completion is run. There are two types of casing guns:  Reusable-carrier Port Plug Gun (PPG)  Expandable High-Efficiency Gun System (HEGS) Both types of casing guns are fully retrievable. Casing guns are designed as systems comprising specific carriers, detonating cords and boosters to provide maximum perforator performance. To ensure the performance meets design specifications, charges are quality control-tested during production in actual gun carriers. Loaded casing guns contain only secondary high explosives (detonating cords, boosters and charges), allowing safe transport and handling when safety procedures are being observed.

2.3.6. Parameters of gun selection After deciding to use wireline casing guns in the completion, the selection of the most appropriate gun depends on several parameters. These are:

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Perforation     

Casing internal diameter Bottomhole temperature and pressure Deep penetrator or big hole application Required shot phasing and density Perforator performance and value

2.3.7. High shot density guns High Shot Density (HSD) guns are another type of carrier guns. They comprise of specific carriers, charges, detonating cords and boosters to provide maximum perforator performance. HSD guns provide increased shot available for natural, stimulated or sand control completions. HSD are the most flexible guns in the field. They are expandable, retrievable carriers and can be run on any type of conveyance (tubing, completion, slick line, TCP, wireline, coil tubing, etc.) HSD gun features:     

Expandable carriers Shot density Helical shot pattern Automatic ballistic connection Firing modes

 Mechanical connections  Exclusive use of secondary explosives  Quality assured HSD perforating guns incorporate shaped charges, detonating cord and detonators. Page 18

Perforation Standard operating procedures must be followed when loading or running these gun systems. Loaded guns should be enclosed in protective tubes during storage to protect the exposed explosives. Three critical tests are performed on HSD perforating guns for reliability testing. These are:  Mechanical / Pressure / Temperature test  Perforating gun Split / Swill test  Drop Test

2.3.8. Through-tubing Guns Through-tubing guns are used primarily for underbalanced initial or subsequent completions that have the tubing and bottomhole assembly already in place. Optimal underbalance can be applied to achieve clean, productive perforations while maintaining absolute well control. The through-tubing guns are designed as systems comprising of specific carriers, charges, detonating cords and boosters to provide maximum perforating performance. Loaded through-tubing guns contain only secondary high explosives (detonating cords, boosters and charges), allowing safe transport and handling when standard safety procedures are being observed. Through-tubing guns include: 1. The hollow carrier guns 2. The exposed guns Types of hollow carrier guns They include Scallop gun systems .these guns are fully retrievable and are the most rigged through-tubing guns, capable of withstanding the highest temperatures and pressures .the hollow carrier guns can be run at very high speeds .enerjet gun are wireline conveyed ,capsule charge type ,perforating guns in the enerjet gun systems each shaped charge is

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Perforation encapsuled and loaded on a strip carrier rather than being enclosed in a hollow tube carrier. This permits larger charges for the same overall gun diameter .Also, due to the greater charge size; enerjet guns outperform hollow carrier guns of the same diameter. enrjet guns are classified into two main types 1.with retrievable carriers 2.fully expendable carriers The retrievable system is designed for rugged conveyance while running down-hole .it provides shot verification.any charge that does not retrived from the well along with the carrier strip .as the carrier is retrieved there is less debris in the well. Expendable systems are useful for applications where well components or conditions make the retrievable of the carrier strip difficult after the gun is shot.

2.4. Explosives Classifications Explosives were invented first by the Chinese in the 10th century, then independently by the Arabs in the 13th century. The low explosive, or black powder, was characterized by slow reaction rates, 500 to 1500 m/sec, and relatively low combustion pressure. Much later, in 1846, the first high explosive was discovered by an Italian, Ascanio Sobreto, and then made commercially by Alfred Nobel in 1867 with the development of dynamite, a combination of nitroglycerin and clayey earth. High explosives, unlike the earlier low explosives, detonate at very rapid rates of 5000 to 9000 m/sec and generate tremendous combustion pressures. The terms low and high explosive are still used to characterize chemical explosives.

2.4.1.Low explosives (propellants) Are used in modern oilfield applications as power charges for pressure setting assemblies, bullet perforators and sample taker guns as well as for stimulation (high-energy gas fracturing, perf wash, etc.). High Page 20

Perforation explosives are found in shaped charges, the detonating cord and detonators, and blasting caps.

2.4.2.High explosives are further classified by their sensitivity or ease of detonation.

2.4.2.1. Primary high explosives are very sensitive and easily detonated by shock, friction or heat. For safety reasons, primary high explosives, such as lead azide, are used only in electrical or percussion detonators in Schlumberger gun systems.

2.4.2.2. Secondary high explosives are less sensitive and require a high-energy shock wave to initiate detonation (usually provided by a primary high explosive). Secondary high explosives are used in all other elements of the ballistic chain (detonating cord, boosters and shaped charges). PETN, RDX, HMX and HNS are secondary high explosives used in oilwell perforating. The rate of reaction, combustion pressure and sensitivity of chemical explosives are affected by temperature. Consequently, maximum safe operating temperatures are defined for all explosives. Exceeding temperature ratings may result in autodetonation or reduced performance. The table below lists the 1- and 100-hr temperature ratings and uses for the various explosives in gun systems.

2.4.3. Effect of temperature Temperature affects the rate of reaction, combustion pressure and sensitivity of chemical explosives. Consequently, maximum safe operating temperatures are defined for all explosives. Exceeding the optimum temperature rating may result in autodetonation or reduced performance. The table lists the 1-hr and 100-hrtemperature ratings and uses for the various explosives in schlumberger gun systems.

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Perforation

2.5. Types of perforation techniques 2.5.1. According to the relation between reservoir and hydrostatic pressures 2.5.1.1. overbalanced perforation main features of overbalanced perforation 1- hydrostatic pressure of fluid in well bore greater than reservoir pressure 2- provide control over well while performing completion 3- perforation can be plugged with debris in well bore "difficult in cleaning process" 2.5.2.2. underbalanced perforation main features of underbalanced perforation

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Perforation 1- Hydrostatic pressure of fluid in well bore is less than the reservoir pressure 2- Well is "Live" after perforation and must be controlled 3- Perforation will be clean from surge into well bore

2.5.2. According to where we do perforation 2.5.2.1.Shop perforated casing are classified to - Round perforated - Slotted perforated In round perforated casing the diameter of slots are 1/8 to 3/8 in and it made by milling or by oxyacetylene torch. The diameter of hole depends on the casing diameter. In slotted perforation the slots are 0.05 to 0.3 inch wide & 1.5 to 3 inch long and it also made by milling or by oxyacetylene torch. And we should take care that the total area of slots equal 2% of casing area. We can also use screen to prevent sand to enter the well. And we prefer slotted casing than rounded one in sandy formations.

2.5.2.2. Gun perforated casing: The second type of perforation is gun perforated casing which is our main point in our study.

Optimum perforation Perforating is a critical part of any well completion process . perforating is the only way to establish conductive tunnels that link oil and gas reservoirs to steel cased well bores which lead to surface . however perforating also damage s formation permeability around perforation tunnels .this damage and perforation parameters like formation penetration hole size ,number of shots and the angle between holes have a significant impact on pressure drop near a well ,therefore, on production .optimization the perforation parameters and mitigating induced damage are the vital aspects of perforating. Ongoing before

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Perforation perforating is less than the formation pressure is essential in removing damage and debris from perforations.

2.5.3.

According to how we do perforation

There are three basic techniques employed today to perforate a well. Although the variations are virtually endless, the following discussion is limited to a basic description of the three techniques. Wells can be perforated using casing guns conveyed on wire line, through-tubing guns, and tubing-conveyed guns. Because each method has advantages and limitations, the completion engineer must choose the most appropriate technique for each well.

2.5.2.1. WIRELINE CASING GUN TECHNIQUES Perforating with a casing gun conveyed on wire line has been a standard technique for many years. Before the tubing and wellhead are put in place, a hollow carrier casing gun is lowered into the well on wire line, positioned opposite the productive zone, and detonated. The main advantages of this system are as follows: - The diameter of the gun is limited only by the ID of the casing; therefore, large, high performance shaped charges can be conveyed in a multiphase, high shot density carrier. - The casing gun offers high reliability because the blasting cap detonating cord and shaped charges are protected from the wellbore environment and the carrier is mechanically strong. - Selective firing is available between guns. - Guns are accurately positioned opposite the zone of interest using a casing collar locator. - No damage occurs to the casing and virtually no debris is left in the well. There are two main limitations to this method: - As a general practice, the well must be perforated with the wellbore pressure greater than the formation pressure. This pressure differential Page 24

Perforation may prevent optimum cleanup of the perforations. The situation is aggravated when perforating in drilling mud. The mud plugs are difficult to remove even when subjected to high reverse pressure. Perforating in clean liquids such as salt water is recommended. - The strength of the wireline and the weight of the casing guns limit the length of the assembly which can be run on each trip into the well. There are three basic types of casing guns: 1. Port Plug Guns 2. Scalloped Guns 3. Slick Walled Guns Each gun design has the same primary purpose to seal the guns from the wellbore pressure and fluids. The differences are in how this is achieved and how the individual charges are secured in place. Port Plug guns are re-usable carriers that use the port plug to secure the charge (Figures B17 and B18). The perforating charge has to penetrate the carrier before it can perforate the casing. Port Plug guns are designed so that the charge perforates a port plug which can be replaced and the gun reused. Gun life is not indefinite but being able to distribute the carrier cost over 10 to 15 jobs reduces the overall cost of perforating. Fig. B18: Port Plug Gun.

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Perforation

Scalloped guns are typically used when high shot density perforating (greater than 4 spf, 13 spm) is required. The carrier is a metal tube with Flat bottomed holes milled on the outside, about 3 mm deep. These scallops are aligned with the perforating charges inside the gun so that the charges fire through the centre of the scallop. This does not significantly change the penetration of the charge but rather is to ensure that any burring that may have occurred on the gun wall does not exceed the overall gun outside diameter. The charges are held in place by a tube or triangular strip (Figure B19) which is slid into the gun itself. The scalloped gun is used for high shot density because the cost of machining so many port plug holes (up to 39 per meter) is prohibitive and the chance of a port plug leaking and flooding the guns is obviously increased. Another common use for the scalloped carrier is for TCP work. Whenever a TCP system is used for a permanent completion, the

Page 26

Perforation guns will not be retrieved, for this case the cost of machining port plugs will not be recovered. Fig. B20: Slick Walled Gun.

The Slick Walled guns are a unique carrier designed for a moderate environment (Figure B20). The gun carriers have neither port plugs nor scallops. It is simply smooth surfaced pipe through which the charges perforate. This causes some burrs on the outside of the carrier but as long as enough clearance exists no problems will be encountered. The carrier and explosives are rated for lower pressures and temperatures Page 27

Perforation than other gun systems (27.5 MPa, 99 degree C for 1 hour) and can only be loaded to a maximum of 13 spm (4 spf). The charges are held in place by a moulded Styrofoam case which allows quick efficient loading. The system allows for cost effective perforating of shallow to medium (2500 m) depth wells

2.5.2.2. THROUGH-TUBING PERFORATING TECHNIQUE In 1953, Humble Oil and Refining Co. pioneered the permanent-type well completion. This technique involves setting the production tubing and wellhead in place and then perforating the well with small diameter guns capable of running through tubing. The main advantages of this technique are as follows: - The well may be perforated with the wellbore pressure below the formation pressure allowing the reservoir fluids to instantly clean up the perforating debris. - Completion of a new zone or a workover of an existing zone does not require the use of a rig. - A casing collar locator allows for accurate depth positioning. The main limitations of this method are as follows: - To allow the gun to run through tubing, smaller shaped charges, with reduced penetrations, must be used. To achieve maximum penetration with through tubing perforators the gun is usually positioned against the casing to eliminate the loss of performance when perforating through the liquid in the wellbore. This arrangement restricts the gun to 0o phasing. - In an effort to improve the penetration performance, gun system designers eliminate the hollow steel carrier and place pressure tight capsule charges on a strip or wire. These guns are called expendable or semi-expendable depending on whether the wire or strip is retrieved. Removing the steel carrier allows a larger charge to be used; however, charge case debris is left in the well after perforating and the casing may be damaged by the detonation. - The charges are exposed in the expendable and semi-expendable systems restricting these guns to less severe well environments and lower running speeds. Page 28

Perforation As stated earlier, these guns, designed to pass through tubing are used for a variety of reasons: 1. Critical sour gas wells where a permanent packer is to be in place before perforating occurs. 2. Older wells where a retrievable packer cannot be un-set due to failure. 3. Perforate slim casings or liners (89 mm). . The small outside diameter of through-tubing guns implies that if the charges are to be contained inside of a tube (HSC) the explosive load will have to be small. Such is the case with our

hyper dome guns (Figure B21). With explosive weights of 1.8 gm to 6.5 gm, penetrations can be limited but exposure to wellbore fluids and potential failure thereby is eliminated. Fig. B22: Enerjet Gun.

If deeper penetration is required, an expendable or semi-expendable carrier is required. Because the gun outside

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Perforation diameter is governed by the charge size, a maximum load can be placed down hole after passing through the tubing. Care must be taken not to attempt too large of an explosive charge. If unenclosed charges in excess of 20 grams are allowed to detonate downhole, casing damage could result. Typical of these carriers is our Enerjet gun where the charges are threaded into a steel bar (Figure B22). Explosive loads can go as high as 15.5 gms and after detonation the steel bar and threaded caps are retrieved from the well. In this manner only a minimum amount of debris, in the form of powder is left behind.

2.5.2.3. TUBING-CONVEYED PERFORATING TECHNIQUE Although various attempts were made to convey perforating guns into the well on tubing it was not until the early 1980's that widespread use of the service began. The basic technique involves assembling hollow carrier steel casing guns vertically with a firing head on top. There are several types of firing heads including drop bar, differential pressure, direct pressure, and electrical wet connect. On top of the firing head is a sub used to allow reservoir fluids to flow into the tubing. A production packer is attached above the fluid communication sub. This entire assembly is then lowered into the well on the end of the tubing string. The string is depth positioned usually with a gamma ray survey. After the guns are positioned, the packer is set, and the well is readied for production. This includes establishing the correct underbalanced condition in the tubing. The guns are then fired and the surge of reservoir fluids is used to clean up the perforations. Depending on the situation the guns may be retrieved or dropped to the bottom of the well. Many variations of the procedure described above are in use today. The main advantages of this technique are as follows: - The well can be perforated with large diameter, high performance; high shot density casing guns with the wellbore pressure lower than the formation pressure (underbalanced) allowing instantaneous cleanup of the perforations. - The wellhead is in place and the packer is set before the guns are fired.

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Perforation - Large intervals can be perforated simultaneously on one trip into the well. - Highly deviated and horizontal wells can be perforated by pushing the guns into the well. The main limitations of the technique are as follows: - Unless the guns are withdrawn from the well it is difficult to confirm whether the entire gun fired. Effective shot detection systems may overcome this limitation. - Explosives degrade when exposed to elevated temperatures, reducing shaped charge performance. It takes many times longer to run a TCP string into the hole than a wire line gun. To compensate, a more expensive and, in some cases, less powerful explosive must be used on TCP operations. - Selective perforating options with TCP are limited. Small intervals over large intervals may not be economical with TCP. - Accurate depth positioning of the gun string is more difficult and time consuming than wire line depth positioning.

2.5.2.3.1. TCP FIRING SYSTEMS Several firing techniques are available for various types of completion or testing operations. They include percussion, pressure, and electrically activated systems.

2.5.2.3.2. Percussion-Activated Firing Head (Drop-bar) The drop bar is the simplest TCP firing system. A cylindrical weight or sinker bar is dropped into the tubing and strikes a percussion- type detonator in the gun firing head. Hydraulic pressure on the tubing fluid column is adjusted to achieve the desired underbalance on the formation before dropping the bar. The bar can be dropped by hand through an open wellhead control valve or contained in a wireline lubricator and released when wellhead valves are opened and can also be run on a slickline.

2.5.2.3.3. Bar Actuated Pressure Firing System The gun is not fired by the impact of the drop bar on the firing head. Instead, the drop bar shears a pin, which releases the catch on the firing piston. The firing piston is then driven hydrostatically towards the percussion cap to set off the detonating train. A minimum hydrostatic Page 31

Perforation head of 500 psi is needed in the tubing to set the gun off. With this feature, it is not possible to accidentally fire the gun at surface by dropping anything on the firing head. If the well is perforated dry, the 500 psi required can be obtained by pressuring the tubing with nitrogen prior to dropping the bar.

2.5.2.3.4. Differential-Pressure Firing Head The differential-pressure firing head utilizes a flowtube through the packer to transfer annulus pressure above the packer to an isolated piston in the firing head located beneath the packer. The advantage of this firing method is that, after setting the packer, the tubing and packer can be tested in the direction of well pressure by internally pressuring the tubing and transmitting this pressure to casing beneath. After Pressure testing, the desired underbalance pressure is fixed before firing the guns. The annulus pressure forces the release piston downward, breaking the shear pins and releasing the locking lugs which secure the firing pin. The hydrostatic pressure in the rathole below the packer then drives the firing pin into the percussion cap, igniting the Primacord which fires the perforating guns.

2.5.2.3.5. Tubing - Pressure Firing System This system uses a percussion-activated firing head similar in principle to the differential pressure and drop-bar systems, except that it is activated by internally pressuring the tubing. This same system is used, without modification, for DST’s or permanent completions. After setting the packer, it is tested by pressuring the tubing annulus. Next, the tubing pressure is raised through three specific pressure cycles to arm the gun. Two of these are redundant safety cycles built into the system to account for unanticipated excursions such as high pressure surges, swab pressures, and high circulating pressures. After the three cycle sequence, there is a variable time delay before firing in order to correct underbalanced pressure and adjust wellhead choke manifolds. An advantage of the tubing-pressure system is that it can be fired in wells where the casing above the packer is leaking; e.g., split or corroded pipe and old squeeze perforations.

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Perforation

2.5.2.3.6. Electric - Wire line Firing System The electric-wire line firing system uses electric current and logging cable for firing. Conventional wire line pressure-control equipment (lubricator, blowout preventer, etc.) is used during flow testing with cable in the hole. The wet connector contains a mechanical latch that secures it to the TCP firing head, preventing the cable from being blown uphole. With these firing systems, an electric current transmitted to a wet connector at the gun head fires the detonator. One of the major advantages of these systems is that they cannot be inadvertently armed and fired before the electric power source is connected with the firing head. A gamma ray and collar log can be run with the electric-wire line firing system.

2.5.2.3.7. JOB PLANNING CONSIDERATIONS FOR TCP

AND

OPERATIONAL

Personnel safety is one of our highest concerns; Schlumberger requires the use of a minimum three meter safety spacer above the gun. This ensures that the guns are below the rig floor when the firing head is connected. Cleanliness is the most important factor governing success or failure of a TCP operation. A dirty workstring with pipe scale, dope, or gelled mud with high solids content can prevent access to any of the firing head systems. Any workstring (new or used) should always be rattled or washed clean before picking up the TCP assembly. Pipe dope should be used sparingly. Once on bottom, circulation should be established to flush trash through the circulating sub. A joint of tubing filled with clean fluid should be run immediately below the circulating sub. If the TCP assembly contains a closed annular production valve and the workstring is filled on the floor with clean brine or diesel while going in hole, circulation is not necessary. In high-angle holes the drop bar should not be used, and pressure-type firing systems are recommended. Gun release subs should be used with permanent completions to allow production logging and access to perforations for remedial stimulation work. If sufficient casing rathole is not available to accommodate the fired guns, they can be pulled out of the well if a stabthrough TCP arrangement is used with a larger bore packer. However, this is not desirable since the well will have to be killed and equipment pulled and Page 33

Perforation rerun. Such a system would likely require guns with smaller OD’s. The optimum underbalance pressure is dependent upon several factors such as perforation size and length, rock strength, reservoir permeability, and fluid viscosity. All of these, in theory, affect the ability of the perforation to be cleaned. As a practical matter, the underbalance pressure should be between a minimum of a few hundred pounds per square inch and a maximum of the design collapse rating for the casing. Low-permeability formations and zones producing gas require larger pressure differentials to clean up the perforations. Some of the most common TCP accessories are listed on the following pages.

2.5.2.3.7.1. Radioactive Marker Sub The sub is run in line with the workstring above the packer, or can simply be a tubing collar or a drill pipe tool joint where one or two small cavities have been drilled and threaded to receive a sealing plug. A radioactive pip tag is installed in each cavity. A pip tag is a very weak gamma ray source (1 microcurie of Cobalt 60). The radiocative marker sub is run above the packer, and all the radioactive material is fully recovered when the string is pulled (Figure B23).

2.5.2.3.7.2.Cone-Type Debris Circulating Sub The debris circulating sub (Figure B24) consists of a ceramic cone seated into a ported sub. The sub is positioned between the packer and the guns, typically 10 m above the firing head. The isolated space below the sub is filled with a clean fluid. Once the assembly above the sub has been circulated clean, the packer is set. A debris circulating sub is often Page 34

Perforation used with a drop bar or a wet connected firing system to prevent debris from settling on the downhole portion of the firing head. The drop bar or female wet connector will easily break the fragile cone to reach the firing head. Fig. B23: Radioactive Marker Sub. Fig. B24: Debris Sub.

2.5.2.3.7.3.Mechanical Gun Release Sub The operating principle of the mechanical gun release sub (Figure B25) is similar to other gun release subs. After a release sleeve is shifted, the lower sub locking fingers retract. The lower sub and the gun string are then released and fall to the bottom of the well. Fig. B25: Gun Release Sub. Fig. B26: Surge-Disc Sub

2.5.2.3.7.4. Surge-Disc Sub The surge-disc sub (Figure B26) features a fragile, high strength, sealed, glass disc inside a sub. The disc is designed to withstand a high differential pressure.

The sub is positioned above the circulating sub, completely sealing off the portion of tubing above it. This portion of tubing can be dry or Page 35

Perforation partially filled with a clean fluid cushion to create an underbalance condition after the packer is set and the disc broken. In the presence of old perforations, the sub can be used with a drop bar firing system. In this application, the underbalance will be established a few seconds before firing the guns. The underbalance will remain effective during firing and at the time of the surge immediately after firing.

2.5.2.4. COILED TUBING CONVEYED PERFORATING FOR HORIZONTAL WELLS 2.5.2.4.1. Principle The principle of this system (Figure B27) is particularly simple: the guns are mounted directly on the end of tubing coiled on a reel in which the electric cable has first been inserted. The connection between guns and tubing ensures the mechanical and electrical bottom link, while on the surface; the cable outlet passes through the shaft of the drum by a rotating device. The lowering and raising movements are provided by the standard coiled-tubing injector head, and the depth measurements are made on the tubing near the injector. This technique is equally capable of conveying small-diameter guns and standard guns, but the performance capabilities will be affected by gun weight. In addition, circulation through the coiled tubing remains available, although the cross section is reduced, owing to the cable.

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Perforation

2.5.2.4.2. Procedure The logging procedure with this system is exactly the same as that for normal use of coiled tubing. Should it be necessary to work under pressure, a lubricator adapted to the guns should be added. The weak link in this system is its relative fragility, rendering it incapable for pushing heavy guns over great distances. Fig. B28: Perforating Depth Control.

2.6.1. WIRELINE DEPTH CONTROL Depth control for perforating is almost universally obtained through radioactivity instruments run in the cased hole in conjunction with the Casing Collar Locator (CCL). The Gamma Ray Log is generally used (Figure B28) though, in some cases, the Neutron Log or both Gamma Ray and Neutron are run. Accurate correlation of radioactivity logs with open hole logs establishes the position of casing collars with respect to the formation to be perforated. A short sub in the casing string is highly desirable to eliminate ambiguities with CCL identification, particularly when all joints of casing are about the same length. If the depth control log is made on a separate trip in the well, the proper shooting depth is determined on the perforating run by recording a second collar log with the collar locator attached to the perforator.

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Perforation

2.6.1.1. Gun-Gamma Ray Tool If the combination Gun-Gamma Ray Tool is used, the entire equipment for depth control and perforating is run on a single trip in the well. The Gun-Gamma Ray Tool includes a rugged, shock proof gamma ray detector. A casing collar locator and a perforating gun can all run together. This offers greater assurance of accuracy and considerable saving of rig time. Depth control should always be used to accurately position TCP guns. A reference radioactive collar is run in the work string and its distance from the top shot is measured. Once on bottom, a through-tubing GR/CCL log is run and compared to open hole logs to establish how guns should be moved for exact positioning opposite the target formation. A variation of this procedure has been used from floating vessels in sand control completions. A sump packer is positioned and set with a wireline and becomes the locating device. The TCP gun string then is run with a locator and collet assembly on bottom. The distance from bottom gun shot to the collet latch is selected to place guns on depth. A radioactive collar should still be run to allow adjustment by logging in case of pipe tally discrepancies or slippage of the sump packer downhole.

2.6.2.2. Precision Identified Perforations P.I.P. tags are used to provide a record of the position of perforations with respect to casing collars and/or formation boundaries. Special shaped charges fired at top and bottom of the perforated section leave traces of radioactive material within the perforations. The top and bottom perforations are then identified by sharp peaks on a Gamma Ray curve after perforating. Small size, low activity and short half-life of radioactive material used in the special charges prevent significant contamination of produced fluid. When run with Gun-Gamma Ray tool and Hollow Carrier perforators, no additional rig time is required other than that needed to log through the perforated interval.

2.6.2. TCP DEPTH CONTROL Four main techniques are used to ensure that the guns are at the correct perforating depth: Page 38

Perforation - Running a through-tubing gamma ray collar locator to locate a reference point in the string and tie into openhole logs. - Setting the packer on wireline at a known depth, and stinging through the guns and completion string. - Setting the packer and guns on wireline at a known depth, and stabbing the completion string in the packer. - Tagging a fixed and accurate reference point such as a bridge plug. The first method is the most accurate. It relies on a radioactive marker sub in the string, and the distance from the radioactive marker sub to the top shot being precisely measured at surface. The string is run in the hole to approximately the correct depth and a short section of GRCCL (Gamma Ray-Casing Collar Locator) log is run over the zone where the sub is located. The gamma ray log indicates the position of the sub (a short radioactive peak anomaly) relative to the formation gamma ray as shown in Figure B30. As the distance from the sub to the top shot is known, the position of the guns can be calculated, and corrected if necessary by spacing out the string at surface. After the packer is set, the gamma ray may be rerun to ensure that the guns are at the correct depth. Fig. B30: TCP Depth Control Log.

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Perforation

As the cased hole gamma ray log can be considerably attenuated, a low logging speed will achieve better correlation results between the cased hole and the open hole gamma ray logs. If the formation gamma ray curve does not show much activity, a radioactive pip tag may be placed As the cased hole gamma ray log can be considerably attenuated, a low logging speed will achieve better correlation results between the cased hole and the open hole gamma ray logs. If the formation gamma ray curve does not show much activity, a radioactive pip tag may be placed in or below one casing joint. (Placement of the pip tag must be included in the casing setting program.) Alternatively, a TDT or a neutron log can be run in place of the gamma ray log.

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Perforation

2.7. GENERAL SAFETY PROCEDURES The following comments are applicable to both TCP and wireline conveyed methods. Additional comments are given in section specific to wireline conveyed perforating. a) All perforating operations, since they involve the handling and use of explosives and possibly radioactive materials, require special safety procedures to be strictly observed at all times. b) Perforating operations should be carried out strictly according to the safety policies of Eni-Agip and the perforating Contractor. In the event of any inconsistency between policies, the most conservative policy will apply. a) Operations involving the use of explosives shall only be performed by Contractor’s specialized personnel responsible for perforation and similar operations. The number of persons involved shall be as low as possible. b) Only perforating Contractor’s personnel are allowed to remain in the hazardous area (gangway, rig floor etc.) during arming of guns. The number of personnel should be limited when the guns are within 500ft of surface when tripping in and out of the hole. c) Any operation involving the use of explosives is not allowed in the presence of thunder, lighting and thick fog, as these are sources of electric potential. d) Explosives shall be kept on site for the shortest possible time, any remaining at the end of the operation shall be removed from the installation. e) Explosives shall be stored on site in proper containers, within a confined area on the rig. Detonators shall be stored in separate boxes, in the same area as explosives. f) Warning signs must be placed around the hazardous area where explosives are used. g) All radio transmitters, radio beacons included, within a radius of 500ft from the well, shall be turned off, (since they may detonate blasting caps), starting from gun arming until perforating guns are 500ft below the sea bottom (similarly, when pulling guns out of hole and guns above 500 ft). All portable transmitters (both Eni-Agip’s and Contractors) shall be placed inside the Eni-Agip office and turned off to avoid accidental transmission. Avoid critical periods of perforating coinciding with arrival and take-off of helicopters. Page 41

Perforation h) Cranes and welding machines shall be put out of service starting from gun arming till gun pulling out and unloading. i) District Office shall be advised by the Well Operations Supervisor on the estimated time of radio silence two hours before starting operations. The Radio Operator shall communicate actual timing. j) Casing perforating can be performed during daylight or at night. However, the first series of shots must be carried out in daylight hours. Before perforating casing, the acceptable cement job quality shall be ascertained by means of CBL/VDL and/or by squeeze jobs. k) Explosives are to be transported unarmed and clearly labeled to the site in secure and protective containers. Extreme care must be applied during loading and off-loading. l) At the rig it is the responsibility of the Installation Manager to ensure that these precautions are taken.

2.7.1.Firing Systems for TCP Operations It is normal practice to run the TCP guns with two firing systems, whenever possible, to improve the chance of a successful operation especially when running the guns on the bottom of a completion. A common combination is to use a tubing pressure actuated system as the primary means of detonating the TCP guns with a mechanical system as the back up. There are four main types of firing mechanisms for TCP guns. Only top down firing mechanisms should be used for safety when arming the guns. The operation of each firing mechanism is:

2.7.2. Tubing Pressure Activated The guns are fired by pressuring up the test string and then bleeding off the pressure immediately. A time delay device is incorporated to allow time to bleed off. This device can be either hydraulic or a slow burning fuse. Some of the firing heads for this system are wireline retrievable which gives another back up option. However, this would preclude the use of the drop bar system as a back up. Although this technique could be expensive on nitrogen, it is well suited to the use of a nitrogen cushion but the time delay on the system will have to be increased to allow time for the nitrogen cushion to be bled off.

2.7.3. Mechanical Impact The TCP guns are detonated by the mechanical impact of a firing bar, which for safety must be run on wireline. (This system is colloquially known as the drop bar system.) Since the system can be affected by debris in the tubing, the completion fluid must be kept clean. The system is preferred as a back up instead of the primary firing mechanism because of the need to use wireline. Page 42

Perforation

2.7.4.Electrically Activated With this system, the guns are fired with an electrically-initiated detonator which must be run on a logging cable. Therefore the pressure control system must be rigged up. Since an inductive or wet electrical connection must be made at the firing head, the system is also susceptible to debris. This system is rarely used on well tests as the only is that the firing heads for this system are wireline retrievable, hence the guns can be run unarmed and, in the case of a misfire, the firing head can be recovered on wireline to determine the cause of the misfire.

2.7.5. Retrievable Slick line Firing Head This type of head was primarily designed to overcome the concerns over about the possibility of guns being denoted by stray pressure or tools/debris/unnamed articles which could fall down through the tubing string and force the detonating pin into the initiator. With this type of head, this possible problem has been completely eliminated due to the design of the system. The guns are run in the hole without the firing head. Then, when ready to arm the guns, the head is run to depth on slick line and latched on to the firing stem or stinger. This system provides its own back-up in that if the firing head does not work, it can be retrieved and a replacement run. Retrievable firing heads are available with mechanical, hydraulic or electric triggering.

Safety Working with explosives is one of the most dangerous professions. While working with explosives you must concentrate on what you are doing. You must perform each step carefully and correctly. Because when shortcuts are taken, when concentration is broken, when communication fails, when respect for explosives is ignored, when instructions in the book are ignored, accidents can happen and they do happen. Safe operating practices are critical to the long-term success of perforating. Any deviation from these procedures can put lives and properties in danger. If precautions are not taken, the danger of premature detonation may occur! Oil and gas are our main sources of energy and in all probability will be for a long time. The oil and gas industry is involved in finding and exploiting underground deposits of oil and gas in addition maintenance Page 43

Perforation of the equipment used to provide a passage for hydrocarbon to flow from reservoir to the surface is also critical. Due to the nature of work involved, hazards typical to the oil and gas industry operations exist. Therefore, in the oil and gas industry work and safety must go hand –In -hand. Safety measurement includes: Properly designed, constructed and tested equipment Well-trained, highly qualified personnel All perforating crew members receive training on the characteristics of the explosives they use and proper techniques for handling and transporting these explosives .perforating engineers and technicians also need to be proficient in the specialized process of gun arming and disarming. They should thoroughly understand procedures and applicable local regulations. In addition, only the engineer or technicians is permitted to arm or disarm the perforating guns on a perforating job.

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Perforation

References - Schlumberger course in open university - B.1 schlumberger papers - B.2 schlumberger papers

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