The literal meaning of perforation is a hole. Perforation in oil and gas industry has a similar meaning in essence. They serve a very important role in the production of these minerals in any type of well.
There are special machinery and processes involved in creating perforations. In fact, a well may not produce without these perforations. So for educational purposes, we’ll discuss what these perforations mean, how they are created, and who is responsible for them in a perforation well.
Perforation Oil and Gas
Perforations are holes or tunnels created between a reservoir and wellbore to create a flow path for the mineral through the casing.
The process of creating these perforations is called perforating. The machines used for this purpose are called perforators.
When a well is dug and cased, it needs to be connected with the actual reservoirs with the oil or gas in a formation. Since there may be different reservoirs surrounding a wellbore, multiple perforations are created. Similarly, multiple perforations may be made for the same reservoir.
The process involves lowering the perforating gun at the required depth where the perforation will take place. The gun then fires on the spot creating a shape charge and blasting energy push that creates a tunnel into the reservoir. The exact process varies by the type of perforation and the method of creating them.
Note that this process mainly occurs after the casing of the well is complete.
Types of Perforation in Oil Well
The types of perforation in oil wells depend on the type of oil well perforators. Essentially, there are three types of perforation methods and perforators.
Casing Gun or Wireline Convey Perforation
This is the oldest way of creating perforations and actually occurs before well. In this process, a casing gun, which is a short-barrel gun, fires a steel bullet. The gun is powered by gas explosives. At first, the wellbore is neutralized to ensure minimal or no damage to the formation in any case.
This perforation method was the first of its kind and became popular beginning in the 1930s. However, it has its limitations as the bullet does not pierce that well in hard formations.
Today, this perforator is only used for soft formations that are easy to penetrate.
Thanks to better technology, now the depth at which the perforator gun works is more accurate. It is run with wireline normally, but also electric lines.
Tubing Conveyed Perforation
This system involves running the perforator gun with the completion string. The perforator gun is fired and left in the well even after firing. For this reason, the drillers drill an additional hole, the sump, to house the gun for the entire duration of the process.
This method has several advantages. The most obvious one is that with the gun left in the wellbore, it can fire multiple perforations in one go without needing to bring up and then drop down again.
This method can even work in unbalanced conditions. It also reduces rig time. However, it can take more time to finalize each perforation.
Through Tubing Perforation
Through Tubing perforation can utilize an existing completion string. However, the catch is the perforator gun must be small, as small as 2 ⅛ inches.
This is one of the quickest methods of creating perforations as it relies on completion string. As a result, it also accelerates production start. More importantly, it’s the most cost-effective method because it doesn’t necessitate completion retrieval afterward.
The only drawback is that the perforation diameter is small, which can impact production levels. However, that can be mitigated with multiple perforations.
Do Perforations Impact Production and Performance of an Oil or Gas Well?
As perforations create the flow arteries between formation and wellbore, they have a drastic impact on oil well performance. However, the perforation itself depends on a number of factors, that, in turn, impact the production and performance.
Here’s what perforations depend on:
- Rock properties and formation conditions (for instance, fracture pressure)
- Minerals in the rock
- Reservoir conditions (pressure, temperature, and flow rate)
- Completion fluid
- Wellbore size and orientation
- Type of casing
- Tectonic stress
You may think that the bigger the perforation, the more fluid will flow into the wellbore, but that’s not always the case. The drilling and well completion companies must determine the appropriate diameter and length of the perforation to ensure maximum but also safe production.
Some Other Terms to Know
Here are some perforations oil and gas-related terms you should know:
High Explosives: These are the explosives that are used for firing perforator guns. Some of the common powerful perforation explosives are RDX, PYX, HMX, and HNS.
Primary Explosive: The primary explosive is smaller-scale initial explosives used to initiate the perforating process. These usually take place in the detonators and are sensitive to firing, so must be performed carefully.
Secondary Explosive: This is the main explosive even though it’s named secondary. These are high-power explosives that create the hole and tunnel through the casing.
Phasing: This refers to the angle between the charges, usually in intervals of 30 degrees. Only specialty guns have this feature.
Perforation Flow Efficiency: This indicates the closeness to the ideal flow levels for the perforation of the given length and diameter. A perforation flow efficiency of 80 percent is good enough to achieve ideal production levels.
Perforations in the oil and gas industry allow the beginning of production. Near or after completion, these perforations initiate the fluid flow into the well. From there, it goes for refining when the fluid reaches the surface.
There are three ways to create perforations, which go back decades. Each method has its pros and cons and may not suit every type of well.