Gas Lift

The PLC Shift Gas Lift application allows you to inject gas down hole in a controlled fashion to increase production from your well. The application uses PID control to set the position of an injection valve to inject just the amount of gas that you want. The application supports multiple control modes, including a plunger mode where gas injection occurs at various times during the plunger cycle.

 

Use the settings in this group to configure the PID that controls the position of the injection valve. These settings are used in all control states. The set point of this PID varies depending on the control mode.

 

Set the 'Gas Lift Control Mode' parameter in the 'Injection Modes' group to 'Continuous Fixed Injection' to select this control mode. Gas is continuously injected down hole at a fixed rate. The injection valve PID set point is the value in the 'Fixed Injection Flow Rate' parameter.

 

Set the 'Gas Lift Control Mode' parameter in the 'Injection Modes' group to 'Continuous Variable Injection' to select this control mode. Gas is continuously injected at a variable rate to keep the well's flow rate above the calculated critical flow rate times a configurable multiplier.

 

The transfer function between the well's flow rate and the critical flow rate set point is controlled by a PID. Use the settings in the 'Variable Injection' group to configure this PID as well as minimum and maximum injection flow rates. Note that this PID is different from the one that controls the position the injection valve. This PID is used to determine the injection rate set point, which is the set point for the injection valve PID.

 

Set the 'Gas Lift Control Mode' parameter in the 'Injection Modes' group to 'Plunger' to select this control mode. In this mode, the gas lift application coordinates with a plunger lift application to optimize production from a well and reduce the usage of lift gas.

 

Any plunger lift application can be used with the PLC Shift Gas Lift application, but using the PLC Shift Plunger Lift application allows for the easiest integration. When using the 'Plunger' mode, input tags in the 'Plunger Tags' group must be correctly driven by the PLC. Without these tags, the gas lift application does not know the state of the plunger lift application and coordination between the two is not possible.

 

When first started, the gas lift application will wait for the 'Plunger Cycle Complete' tag in the 'Plunger Tags' group to go true before injecting any gas. This is to ensure that the gas lift application is synchronized with the plunger lift application.

 

As the plunger program moves through its various control states, the PLC Shift Gas Lift application can be configured to inject gas that is specific to the plunger state. These states are discussed below.

 

Use the settings in this group to configure injection when the sales valve is closed and the well is shut in. Injection can be configured to start when the casing pressure is less than a certain value and to stop when the casing pressure is above a certain value, saving lift gas.

 

Use the settings in this group to configure injection when the sales valve is open but before the plunger arrives. Using this state requires that there is a plunger installed in the well. This state also allows for automatic optimization of the amount of lift gas used. Lift gas usuge is reduced when the plunger arrives early, and is increased when the plunger arrives late. The goal is for normal plunger arrival.

 

In this state, you can choose from fixed injection or variable. These are similar to the control modes discussed above.

 

In the fixed injection mode, gas is injected at a fixed rate that depends on the previous plunger arrival type. For each arrival type, including early, normal, late or no arrival, you can configure how much gas to inject this cycle. Normally, when the plunger arrives early, less gas can be injected, and when the plunger arrives late or does not arrive, more gas is injected.

 

You can optionally enable optimization when using fixed injection. Use the settings in the 'Plunger Pre-Arrival Injection Optimization' group to configure how optimization works. When optimization is enabled, the injection set point will be adjusted automatically depending on the previous arrival types.

 

In the variable mode, gas is injected to keep the well flowing above the calculated criticial flow rate times some multiplier. In the variable mode, use the settings in the 'Variable Injection' group to configure the PID that is used to determine the injection flow rate set point.

 

You can optionally enable optimization when using variable injection. Use the settings in the 'Plunger Pre-Arrival Injection Optimization' group to configure how optimization works. When optimization is enabled, the critical flow multplier will be adjusted automatically depending on the previous arrival types.

 

Use the settings in this group to configure injection when the sales valve is open and after the plunger has arrived if there is a plunger. If there is no plunger, settings in this group apply as soon as the sales valve is opened. In this state, you can choose from fixed injection or variable. These are similar to the control modes discussed above.

 

In the fixed injection mode, gas is injected at a fixed rate. In the variable injection mode, gas is injected at a variable rate that keeps the well flowing above the calculated critical flow rate times some multiplier. In the variable mode, use the settings in the 'Variable Injection' group to configure the PID that is used to determine the injection flow rate set point.

 

View the application's diagnostic for detailed troubleshooting information. See the 'Log Files' section for more details.