Choke valves can withstand pressure drops of up to 500 bars under severe operating conditions. Fluid mixtures of hydrocarbon liquids and gases can be pumped through these valves without causing an erosive reaction.
The use of choke valves in oil and gas reserves is widespread. Valves are indispensable in the oil and gas industry to control the flow of liquids or oils from wells. The valves seen in wells for oil and gas production can be seen in wells for producing oil and gas. As well as regulating the downstream pressure in a pipeline, the choke valve can remove stress from a reservoir.
Construction of choke valve
To better utilize natural gas, chokes hold back pressure on flowing wells so that they can lift and control the pressure in the bottom hole. Vertical pipe flow occurs when the hydrostatic head decreases, causing gas to expand rapidly and liquid to move in slugs.
Due to this, the potential lift energy of the gas is quickly lost. Over time, the liquids accumulate over the perforations as the liquid falls back. Pressure is held back on the formation by these accumulating liquids. In the event of too much liquid accumulation, the well may stop flowing and die.
As the flow opening at the wellhead is restricted, the choke holds back this backpressure. It is the backpressure that prevents the gas from expanding and rising uncontrollably. This way, the gas is dispersed in the liquids as it travels through the tubing.
It is possible to have a variable or a fixed opening on a choke. A set of openings is called a bean, which is a short tube for flow. 1/64ths of an inch were measured during graduation. Gas wells with minor to moderate rates usually have flow sizes of 8 through 20 (in 64ths).
In addition to reservoir pressure, tubing size, gas volume, and liquid density, the choke size are influenced by reservoir pressure, tubing diameter, and gas volume.
An increasing width slot design may be used in variable chokes to facilitate quick resetting. The choke size can change over a day on well-cleanups following stimulation. In addition to periodic liquid unloading, they can also be used to alter choke sizes frequently.
Working of the choke valve
The choke valve closely resembles the cut-off valve in terms of its appearance and structure. Their only difference is the disc’s shape and the working stroke’s length. It is for this reason that choke valves and cut-off valves are highly interchangeable.
Some shut-off valves, regardless of their type, can alter the cross-sectional area of medium channels and thus adjust the track to some extent, but their adjusting capability is not as good as some other kinds.
In order for the open-close parts and the valve stem to be movably connected, there is a gap at the joint, which makes adjustment difficult; lifting the open-closed legs doesn’t change proportionally with changes in the channel area, so it’s hard to adjust them continuously and accurately. In small channels with a large medium flow rate, the sealing surface will erode severely, which will result in a vibrating disc. It is, therefore, common to use choke valves with unique structures and an open-close shape to adjust and ensure smooth operation.
What are the types of choke valves?
In the oil and gas industry, there are two types of choke valves: a non-regulating choke valve and a regulating choke valve.
1. The Regulating choke valves
A choke valve of this type manages the flow levels in the flow lines and the production header with flow control valves. Through the control panel, the downstream flow lines can be controlled by activating the regulating choke valve based on the electric signal. The valve is an automatic valve that can be operated by electricity.
2. The Non-regulating choke valve
Choke valves of this type work the same way as ON-OFF valves, removing the pressure from the reservoir to a level required in the flow path. It is designed so that when it is fully open, the choke valve can remove stress. In this case, it is impossible to regulate the flow with these valves because they are not designed or sized.
During times of depletion of reservoir fluids, reservoir pressure drops in oil production wells. Therefore, removing the non-regulating choke valves is necessary to maintain the excellent production levels as the reservoir pressure drops. The non-regulating choke valves in oil production wells can be replaced with valves that have larger flow openings during the production process.
Common problems of the choke valve
Most choke failures occur as a result of solids in the produced fluids. It is possible for sand, scale, ice, corrosion particles, and other solids to abrade the choke restriction, causing the well to become overloaded and die. In large pressure drops, solids are more likely to irritate the choke and cause cavitation. These situations are usually characterized by choke life measured in minutes. It is recommended to drop pressure gradually across three or more choke sets in series if you are going to lower stress at high pressures.
When moving from 5000 psi to atmospheric pressure, the gas expands 340fold, increasing its velocity by the same amount. The volume increases 136 fold when 5000 pounds of pressure are dropped to 3000 pounds, 150 fold when 3000 pounds of pressure are dropped to 800 pounds, and 54 fold when 500 pounds of pressure are dropped to atmospheric pressure. There is a 340-fold drop in total, but velocity increases across any choke are considerably smaller.
Applications of the choke valve
- The flow line must operate at a very high operating pressure.
- In petrochemical plants, it is used to handle steam and CO2.
- Hydraulic fracturing and drilling mud applications in the oil and gas industries.
- Reserves of oil and gas.
- The well heads of production wells
- The Christmas tree can be reinjected with gas
- Various chemical industries use surface and subsea manifolds to handle crude oil, gas, water, and sand mixtures.
- Loading vessels for FPSOs.
FAQs (Frequently Asked Questions)
What is the purpose of a choke valve?
The purpose of choke valves is to reduce pressure and control the flow rate of produced fluids further downstream. By keeping operators away from the wellhead, chokes effectively minimize the likelihood of downstream equipment being damaged, provide longer production times, and alleviate field operator stress.
How is the choke valve controlled?
Controlling choke valves work by sending a signal to the control panel that opens or closes the valve to regulate the flow in downstream flow lines through an electronic or pneumatic signal. Choker valves can also be used in liquid lines operating at very high pressures, among other applications.
What is the best way to open or close a choke?
An engine is only started with the choke when it is cold. It is best to close the choke when starting a cold engine to limit the amount of air entering the engine. When the engine is trying to warm up, this increases the fuel in the cylinder and helps it run longer.