How to Commission Gas-Lift Valve Pressure Telemetry

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Verify Each Transmitter Reads True

Start with the casing pressure transmitter, which reads the gas injection pressure in the annulus. Confirm it is plumbed to the casing, isolated correctly, and reading against a known-good test gauge on the same tap. The reading should agree with the gauge within the transmitter's accuracy; a large offset means a zero problem, a blocked impulse line, or a wrong range. This casing pressure is the primary signal that tells you what the injection system and the gas-lift valves are doing, so it has to be trustworthy first.

Repeat for the tubing pressure transmitter, which reads the flowing wellhead pressure on the production side. Verify it against a test gauge on the tubing tap, and confirm its isolation and impulse line are clear. Tubing pressure fluctuates more than casing pressure on a producing gas-lift well, so do not expect a rock-steady reading, but it should agree with the gauge at the moment of comparison and respond when the well's flow changes. A tubing transmitter that never moves is likely blocked or isolated.

For both transmitters, confirm the analog signal is healthy and not pegged. A 4-20 mA transmitter reading at or beyond either end of the range indicates an over-range, an open circuit, or a short rather than a real pressure, and it must be resolved before scaling. Treat each channel as a standard analog input loop check in addition to the pressure comparison, so you catch a wiring fault before it masquerades as a pressure reading.

Scale the Channels and Set Alarms

Scale each channel to its transmitter's calibrated range so the SCADA reads true engineering units. Enter the transmitter's zero and full-scale pressures exactly, and verify by comparing the scaled value against the test gauge at two points if you can vary the pressure, or at least at the current pressure. A scaling error puts every pressure off by a proportion, which will later be misread as a valve or injection problem, so confirm the units before setting any alarm on them.

Set alarm limits around the well's expected operating pressures, supplied by the production engineer or the gas-lift design. Casing injection pressure typically sits near a design injection pressure, so alarms bracket that value to catch a lost or excessive injection supply. Tubing pressure alarms bracket the normal flowing range to catch the well loading up or dying. Set the limits with enough margin that normal fluctuation does not trip them, applying the same deadband discipline you would to avoid a nuisance alarm flood.

Relate the casing alarm to the injection setpoint deliberately. Because the gas-lift valves open and close based on the relationship between casing and tubing pressure, an injection pressure that drifts outside its intended band changes which valve is passing gas. Setting the casing alarms with the valve design in mind, rather than as arbitrary round numbers, means an alarm actually corresponds to a change in valve operation. Keep the concept of casing head pressure in gas lift front of mind when choosing the limits.

Confirm the Trends Behave Sensibly

With both channels scaled and alarmed, watch the live trends for long enough to confirm they behave like a gas-lift well should. Casing injection pressure should sit relatively steady near its setpoint, moving slowly as injection rate or valve status changes. Tubing pressure should show the normal fluctuation of a flowing well and respond to changes in production. If casing pressure is jumping erratically or tubing pressure is dead flat, the telemetry is not yet trustworthy regardless of the calibration.

Confirm the two pressures make physical sense together. On a healthy gas-lift well the injection casing pressure is higher than the tubing pressure at the point where gas is entering, and the pressures move in patterns the gas-lift design predicts. If casing and tubing pressures cross in a way the design does not allow, or move in lockstep when they should be independent, suspect a plumbing swap or a scaling error rather than a real well event. The relationship between the two channels is itself a verification.

Finally, capture a baseline of the normal casing and tubing pressures once the well is stable and injecting properly. This baseline is the reference against which every later change - a valve shifting, injection being lost, or the well loading up - becomes visible on the trend. Storing both pressures as monitored, trended tags turns the commissioned telemetry into the diagnostic backbone of the gas-lift well, and it is the point of commissioning the telemetry at all.

Common Mistakes

The most common mistake is scaling a channel to the wrong transmitter range, so every pressure is off by a proportion and later reads as a valve or injection change. Always confirm the scaled value against a test gauge before trusting the number or setting alarms on it.

The second is swapping the casing and tubing plumbing or tags, which makes the two pressures behave impossibly relative to each other; confirm they make physical sense together as a cross-check. The third is setting alarm limits too tight, so normal tubing fluctuation floods the operators with nuisance alarms and the real events get lost in the noise.

Frequently Asked Questions