perforation(2) (Detonators)(guns)

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 non-electric 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 radio-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 also uses an EFI. it does not contain primary high explosives or a down-hole 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:

·        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. 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 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.