Gas Lift Module, Petroleum Production Performance series - Part 3

Transcript: The types of valves to be used for intermittent lift depend upon whether we are going to install a single point for multipoint injection system. In single point intermittent gas lift operation, all of the gas necessary to move the liquid slug to the surface is injected through the operating valves, generally the bottom valve in the string. Let's look at a single point injection on the gas lift simulator. For this type of installation, the valve should expand to a large port size as soon as it is open and remain in the fully open position until closing. Depending upon the completion configuration, the port side will range in diameter from ⅜ to ⅘ of an inch. For multipoint intermittent gas lift operation, each valve intern should allow sufficient gas to pass so as to move the slug to the next higher valve. The pressure under the slug opens the valve that has just passed and supplements against being injected through the lower valves.

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As the slug moves to the surface, the valve normally remains opened until the slug is produced at the surface. Because the opening and closing of the various valves in our gas lift systems are so important to its operation so we should understand how and when a valve will open, when it will close and what a difference in these two pressures. Here we have a casing pressure operated valve; it is a single element valve for which we would like to calculate the opening and closing pressures. To do this,

Click here to see the example (1:44 – 4:28)

For given bellows and tubing pressures, we may reduce the spread by reducing the size of the poor opening. This is particularly important in intermittent gas lift installations because it controls the volume of gas used in each cycle. As the pressure reduction or spread required to close the operating valve increases, remaining gas injected during the cycle also increases. A small port size though increases horsepower requirements and therefore a balance must be done between gas conservation and horsepower requirements. The pilot valve was developed in response to the need for a larger ports size while maintaining cost control over spread characteristics. It has a small port which is used for split control and a larger port which is used for more efficient gas passage. The pilot valve then answers this twofold need and as often used for intermittent gas lift operations.

Click here to know about the operation of a pilot valve. (5:31-8:13)

Let me summarize this section on valves. A gas lift valve is categorized according to the pressure which has the greater effect on its opening. The casing pressure or pressure operated valve is dominated by the casing pressure both to open enclosure. The fluid operated valve depends on the tubing pressure to open and close it. The throttling valve or alternatively the continuous flow valve depends on the casing pressure to open it and the tubing or casing pressure to close it. See the whole video for more…

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