Stimulation or well stimulation is an important part of oil and gas extraction and production. There’s a lot that goes on from when an oil or gas field undergoes discovery to the time it starts producing the valuable minerals. Those minerals are then used for energy purposes and making hundreds of thousands of different products.
There are several different well stimulation techniques over the many decades since oil wells and gas fields became common around the world. In this article, we’ll explore and study everything about stimulation, in general, in the oil and gas industry.
What is Well Stimulation?
Well stimulation (or simply stimulation) is a treatment process to enhance or repair the productivity of a well. It basically creates or improves the flow of the mineral underneath the ground. The minerals flow from the reservoir in the formation to the wellbore, from where they are pumping out of the ground and will go transportation.
Stimulation typically follows drilling and completion. When a well is drilled and completed, the surrounding formation can be damaged. When the formation has penetration, debris and leftovers from the drilling and completion techniques can reduce the permeability of the natural pore throats.
In simple words, the flow of the mineral decreases because of the presence of debris from earlier stages of well construction.
Types of Oil Well Stimulation
Well stimulation falls under two categories: hydraulic and matrix. Essentially, there are three types or methods of well stimulation.
- Explosive Fracturing
- Acid Injection
- Hydraulic Fracturing
Let’s discuss each of them.
Explosive fracturing, as the name indicates, uses controlled explosions to pave the way and remove the blockage of flow. Also called well shooting, this method uses chemical explosives.
It’s one of the oldest well stimulation techniques, which is also one of the most aggressive and risky. Supersonic waves from gases with a lot of pressure force the fluids to come out of the formation. The blast takes place at the mouth of the well.
This method is not as accurate as of the other oil well stimulation methods. Although the explosions are technically fully controlled, it’s difficult to achieve a higher rate of accuracy. There’s always a risk of further damage.
This is why major oil and gas companies have retired this method for newer, safer methods.
Acid injection is another popular method of well stimulation. It basically involves acidizing well stimulation with hydrochloric acid (HCL). The acid is pumped into the wellbore, where it helps dissolve hard minerals like calcium carbonate.
As the calcareous mixture dissolves, the channels of the well open, and the flow gets better. Oil or gas can then easily flow from the formation to the wellbore.
While it’s environmentally safe most of the time, it does require precision and care to ensure there are no leaks or contaminations from the acid. It has a lesser environmental impact than explosive fracturing.
Hydraulic fracturing or fracking is the most common method for well stimulation today. The US uses hydraulic fracturing in more than half of its onshore wells today. It was hydraulic fracturing that made shale oil extraction possible in the first place.
Fracking involves the pumping of high-pressure liquid to penetrate the formation, especially rocks. This liquid is called fracking fluid and mainly contains water and sand, among other proppants.
The pressure creates cracks in the formation, allowing the oil or gas to flow out freely. Even after the hydraulic pressure ends, the small proppants like sand keep the fractures open. As a result, hydraulic fracturing is more effective and long-lasting than acidizing well stimulation.
Hydraulic fracturing isn’t just beneficial for new wells but can also stimulate more production from old wells that ceased to produce. Therefore, this kind of stimulation allows companies to utilize the full potential of an oil well or gas field.
The fracking fluid typically contains 90 percent water, 5 percent sand, and the rest are chemicals like aluminum oxide.
Hydraulic fracturing has proven highly successful with shale oil, as oil shales cannot be penetrated using traditional methods. Their natural flow is almost nonexistent as the hydrocarbons cannot flow out of the rock formations into the wellbore on their own; they must be stimulated.
The risk of contamination is very low as compared with the other two common techniques for increasing flow and repairing damage post drilling.
Why is Well Stimulation Important?
As discussed above, stimulation may not only be necessary for new wells but also existing ones. A reservoir that requires stimulation is classified as unconventional because it doesn’t have a consistent or speedy natural flow.
Just getting to the rock formation and the reservoir in it is not enough to yield ample production. For instance, if the natural flow to the reservoir is slow, the oil or gas retrieval may not be go replenishment soon enough. That would translate into very limited production that may not even be profitable enough to have a well in the first place.
So the different techniques of stimulation help penetrate the formation and remove impurities and debris that collect as a result of post-stimulation processes.
Fracturing also helps increase the flow of wells that have been in production for some time. Over time, the flow rate can reduce, but that doesn’t mean the oil or gas well has depleted completely. Hydraulic fracturing, in particular, can restore their productivity, making them profitable once again.
As is the case with most oil and gas well phases, stimulation can also be very expensive. However, with better technologies, companies are making this process more cost-effective, as well as, reducing its environmental impact.
Well stimulation or reservoir stimulation is crucial for initiating and restoring the productivity of an oil or gas well. Hydraulic fracturing is the most common method today, especially with the advent of shale oil.
While there are challenges with all the methods, fracking is the most efficient. So it’s no surprise that its use is more common now. With that, explosive fracking and acid injection are still useable for stimulating wells where necessary.