The process of catapulting through casings and cement rings with special perforation to generate holes in the rock body and establish a communication channel between the formation and the wellbore to promote the reservoir fluid into the wellbore is called perforation.

1. The purpose of perforation

After the cementing is completed, there is a layer of casing and cement ring between the wellbore and the formation, and there is also a part of the near-well area contaminated by mud, The main purpose of perforation is to penetrate the casing and cement ring, open the reservoir, establish the connection between the formation and the wellbore, so that the fluid can enter the wellbore, to realize the normal production of oil and gas wells.

2. Perforating equipment

Perforating equipment includes fireworks and non-fireworks. Pyrotechnics refers to components that can produce explosions and achieve predetermined functions under external energy stimulation. Including perforated projectiles, detonating cables, detonating tubes, detonator retractions, electric detonators, impact detonators, time-lapse gunpowder, composite gunpowder, cluster gunpowder, bridge plug gunpowder, tail bombs and bulkhead gunpowder, etc.;

Non-fire products include perforating guns, gun joints, oil pipes, glass plate joints, pressure opening devices, shock absorbers, radioactive joints, ignition rods, etc.;

3. Current status of perforation technology

At present, perforation technology at home and abroad can generally be divided into the following categories: (1) High-efficiency perforation focusing on improving oil and gas production capacity, such as concentrated perforation, composite perforation, etc. (2) Perforation technology focusing on protecting reservoirs and improving perforation completion effect, mainly including negative pressure perforation, dynamic negative pressure perforation, super-positive pressure perforation, and directional perforation; (3) Integrated operation process focusing on improving operational efficiency, including combining perforation and testing, perforating with acidification, and perforating with fracturing to improve the reliability of test results; (4) Operation process aimed at improving operation safety and efficiency, including pipe string safety design, operation optimization design, intelligently guided perforation, perforation monitoring, and diagnosis.

Status of perforation technology:

Deep penetration into shaped energy perforation

Initially, the bullet perforation method was used to penetrate the casing and cement ring, connecting the target area and the casing. However, the bullet can penetrate at a very limited depth and often fails to form effective bullet holes. Practitioners invented deep-penetrating-shaped perforation technology by borrowing the penetration capabilities of anti-armor weapons. This perforation technique has a Mohoput effect and has good rock-breaking ability, which can significantly increase the perforation depth. In recent years, with the in-depth development of unconventional oil and gas resources, the requirements for perforation are getting higher and higher, and oil service companies around the world have increased their research efforts on deep penetration shaped perforation technology, and the average penetration depth of perforation has also been greatly increased. The most representative model is the 4039RaZor HMX perforating projectile developed by GEO Dynamics in the United States, which has an average penetration depth of about 1600mm for concrete targets; The perforated projectile developed by Owen in the United States has an average penetration depth of about 13400mm for concrete targets.

Composite perforation technology

Composite perforation technology provides secondary perforation energy through composite propellants. While the shaped perforating projectile forms a connecting channel between the reservoir and the casing, the composite propellant is ignited to produce a high-temperature and high-pressure gas, which is released through the discharge hole on the perforating gun and immediately flows into the perforation channel, thereby effectively fracturing the reservoir. Through this process, an extended fracture network will be formed in the near-well area, which greatly improves the fluid conduction capacity in the near-well area. The original primary charge structure gradually evolved into a secondary and tertiary charge structure, which further increased the composite perforation power. The average crack length in simulated target practice nearly doubled compared to the previous structure. In addition, multi-stage pulse composite perforation based on delayed ignition technology and ignition control technology have been developed and applied to oilfield perforation operations, which can further improve the perforation efficiency by controlling the working time of multi-stage perforation. Composite perforation technology has been developed into a variety of types such as built-in, suspended, and wrap-around, as well as different product series such as deep penetration, large caliber, and high-density perforation. In addition, process technologies such as perforation acidification integration, perforation and DST integration, and horizontal well-integrated perforation have been formed

Directional perforation

Directional perforation uses special directional devices or facilities to realize the control of perforation direction, optimize the perforation design, and improve the operation efficiency, mainly divided into vertical well-directional perforation and horizontal well-directional perforation. During reservoir development, conventional perforation usually opens cracks horizontally. However, in actual reservoirs, there are usually inclination angles α1 and α2 between the maximum principal stress direction and the horizontal direction of the reservoir. Sometimes it is necessary to use a gyroscope or rotating perforation tube column to point the perforation direction to the main direction, to reduce the fracturing pressure of the later modified reservoir, reduce the difficulty of fracturing, and improve the perforation efficiency. At the same time, it can increase the effective oil discharge area of the reservoir and improve the production capacity of the oil well. Cable conveying perforation can be applied to wellbores with a slope of less than 30°, and the operation accuracy and efficiency are much higher than those of tubing transportation. In the perforation process of long horizontal wells, to ensure the safety of operation, it is necessary to use corresponding one-way or two-way delay detonators and ultra-long horizontal intervals can be realized by segmented detonation.

Dynamic negative pressure perforation technology

The dynamic negative pressure perforation technology under the current situation requires the design of negative pressure in the wellbore, so that the wellbore pressure can be lower than the pressure of the formation, and the pressure difference formed between the formation and the wellbore is applied during the perforation process so that the rapid impact return can be effectively generated. In the process of applying dynamic negative pressure perforation process technology, the negative pressure chamber (1 set) is connected based on its perforating gun part, and the explosion energy formed in the perforation process can quickly open the negative pressure chamber, and then let the perforated layer casing annular liquid be inserted from the negative pressure chamber at the first time, and finally the negative pressure is effectively generated based on the casing annulus. To sum up, the main advantages of dynamic negative pressure perforation technology include: first, the negative pressure generation method is simple, and the on-site operation process is simple; Second, it can be used with dynamic negative pressure perforation design software, thereby improving the application value of the technology.

Well Completion: Perforation – YouTube