In a continuous-flow gas-lift well, gas is meant to inject through a single point at the bottom of the string, and that point is the orifice valve, also called the operating valve. Unlike the pressure-charged unloading valves above it, which are engineered to open and close during startup and then stay shut, the orifice valve is a simple fixed opening that passes gas continuously. Understanding the difference between the operating orifice and the unloading valves, and knowing how to read whether the well is injecting stably through that orifice, is central to running a continuous gas-lift well well.
Gas Lift Orifice Valve and Operating Point in one line: A gas lift orifice valve is the operating valve at the deepest injection point of a continuous-flow well - a fixed opening that passes injection gas continuously into the tubing. It differs from the pressure-charged unloading valves above it, which close after startup, and injection-rate and casing-pressure trends confirm the well is holding a stable operating point through the orifice.
A continuous gas-lift string carries two kinds of valves that do very different jobs. The unloading valves, higher in the string, are pressure-operated devices - typically charged with a dome pressure or held by a spring - designed to open and close in response to injection and tubing pressure during the unloading sequence. Their entire purpose is to walk the injection point down during startup and then close, so that once the well is unloaded they take no further part in normal operation. They are dynamic devices with a job that finishes at the end of unloading.
The orifice valve at the bottom is fundamentally simpler. It is not a pressure-charged device that opens and closes; it is essentially a fixed-size hole - an orifice - that gas flows through whenever injection pressure is applied. Because it does not need to close during unloading, it does not carry the pressure charge that the unloading valves do. Its size is chosen to pass the design injection-gas rate at the well's operating conditions, and once the well has unloaded to it, it simply stays open and injects continuously.
The reason continuous-flow wells inject through a fixed orifice rather than a pressure-operated valve is stability. A continuous well wants a steady, unvarying injection point and injection rate, and a plain orifice delivers exactly that - it does not hunt, cycle, or transfer once the unloading valves above it have closed. The pressure-operated unloading valves are there only to get the well down to the orifice; the orifice is where the well lives during production. Keeping that distinction clear explains why the deepest valve behaves so differently from the ones above it.
The orifice valve defines the point of injection - the depth at which gas enters the tubing during steady production - and by design that point is as deep as the injection pressure and completion allow. Depth matters because the deeper gas enters, the longer the column of fluid it lightens, and the lighter that column, the lower the flowing pressure at the sandface and the greater the drawdown the reservoir sees. A deep operating orifice therefore translates directly into more production, which is why so much of gas-lift design is about getting the injection point as low as possible.
The orifice's position at the bottom of the valve string is the endpoint the entire unloading sequence works toward. Every unloading valve above exists to lighten the column enough for injection to reach the next depth, and the sequence is finished only when gas is passing through the orifice with all the unloading valves closed above it. If a well cannot reach its orifice - because of spacing, insufficient injection pressure, or a heavy fluid column - it injects through a shallower unloading valve instead, lifts a shorter column, and produces less than its design.
Because the orifice is a fixed opening, the injection rate through it is governed by the pressure difference across it - casing injection pressure on one side, tubing pressure on the other - and by the orifice size. That makes the operating point of a continuous gas-lift well a balance: the orifice passes whatever rate that pressure difference drives, and the resulting lightened column sets the tubing pressure, which in turn affects the pressure difference. A stable operating point is one where those settle into a steady, self-consistent condition, injecting the design rate through the orifice at the design depth.
Whether a continuous gas-lift well is holding a stable operating point through its orifice is something the surface pressures and rates reveal, and it is a natural thing for a SCADA system to watch. The two most telling signals are the injection-gas rate and the casing (injection) pressure. A well settled on its orifice shows a steady casing pressure and a steady injection rate - the fixed orifice passing a constant flow against a stable pressure difference. Trends that hold flat are the picture of a well lifting cleanly from its operating point.
Instability shows up as movement in exactly those signals, and its pattern points at the cause. If casing pressure and injection rate begin to swing or cycle, the well may be multipointing - injecting through more than one valve because an unloading valve has failed to stay closed - or it may be heading toward instability where the injection point wanders. A cloud SCADA platform such as Merobix trending casing pressure, tubing pressure, and injection rate together lets an engineer see those swings develop and distinguish a stable single-point operation from a well that is cycling or injecting through the wrong valve.
That continuous, remote visibility is what makes the operating point manageable rather than merely assumed. Historizing the injection pressure and rate builds a record of what stable operation looks like for a given well, so a departure from it - a creeping casing pressure, a wandering injection rate, a change in production at constant injection - stands out against the norm. On remote wells that no one visits for days, watching the orifice's operating point through those SCADA points is how an engineer confirms the well is still injecting deep and steady, and catches the shift to unstable or multipoint injection before it costs meaningful production.
An unloading valve is a pressure-charged device that opens and closes during the unloading sequence and then stays shut during normal production. An orifice valve is essentially a fixed-size hole at the deepest point that passes gas continuously and does not open or close. Unloading valves get the injection point down to the orifice; the orifice is where a continuous-flow well injects during steady production.
A continuous well wants a steady, unvarying injection point and rate, and a plain orifice provides exactly that because it does not hunt, cycle, or transfer once the valves above it have closed. Its fixed size passes the design injection rate at the operating pressure difference and simply stays open. This stability is why the deepest valve in a continuous string is an orifice rather than a pressure-operated valve.
The clearest indicators are a steady casing (injection) pressure and a steady injection-gas rate, which together show the orifice passing a constant flow against a stable pressure difference. Swinging or cycling in those signals suggests instability or multipoint injection through a valve that failed to close. Trending injection pressure and rate in SCADA lets an engineer confirm steady single-point operation and catch departures from it.
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