Design is the most critical step in the gas lift process. PCS utilizes its OPTIpod software to design highly effective gas lift systems for today and the future. Using a number of well characteristics, we determine the optimal amount of gas to deliver fluids to the surface and the best locations, based on pressure, for the gas to be injected. Also paramount is recommending the method of gas lift that will be most effective. Continuous flow gas lift is the most common application, but there are other types of installations that address special conditions.
Continuous Flow Gas Lift
Continuous flow gas lift is most commonly recommended and is ideal for wells that produce at higher rates and with higher reservoir pressures. In the continuous flow gas lift well, the compressed gas is continuously injected to increase reservoir drawdown and subsequently maximize production.
Intermittent Gas Lift
For wells that produce at relatively low rates or have low reservoir pressure, intermittent lift is often a better solution. As the name implies, intermittent gas lift injects the gas in cycles. Between injections of gas, the reservoir produces a liquid slug. To remove the slug, the gas is introduced below it and in a single burst of high pressure. The gas expands quickly, forcing the slug to the surface. The injection stops and the slug clears the surface. The reservoir pressure builds again, producing another slug, and the cycle is repeated.
Gas Assisted Plunger Lift (GAPL)
Gas lift can be used to assist plunger lift in wells with specific characteristics. In a well with flowing bottom hole pressure (FBHP) that is just below what is required to run plunger lift, a PCS Flow-thru Plunger Lift system can be installed in the well and aided by continuous flow gas lift. If the conditions are right, this can be an effective way to lower the amount of injected gas and consequently the compressor costs associated with traditional gas lift. When liquid fallback is excessive, plunger lift might be recommended in conjunction with an intermittent lift installation. In this application, the plunger minimizes injection gas breakthrough and is particularly applicable when the injection gas pressure is low and the point of gas injection is deep.
Casing (Annular) Flow
A casing flow installation is one in which gas is injected down the tubing string, and well fluids are produced out the casing. Particularly efficient in high-volume, continuous flow wells, this application is recommended when very large amounts of fluids' at volumes exceeding the tubing capacity must be removed.
Gas Lift for Long, Perforated Intervals
As more and more wells are being drilled and completed with long perforated intervals, liquid loading and pressure build-ups often occur as the result of inadequate velocities in the casing. This can negatively impact the effectiveness of gas lift.
For optimum reservoir drawdown in wells with long perforated intervals, PCS offers several alternatives to more costly re-fracturing or well abandonment. When declining reservoir pressures and lower flow rates lead to liquid loading in the long perforated interval, PCS latest advancements to its Opti-Flow Gas Lift systems create adequate velocity below the packer to recover all fluid and maintain the lowest possible FBHP and most efficient operation.
PCS has refined several innovative methods where gas lift can now be introduced to a deeper point in the well to maintain adequate velocities and ensure optimum production rates without applying additional back pressure on the formation.
Annular Bypass Assembly (ABA)
The Annular Bypass Assembly is a hybrid of the conventional gas lift system with a packer, and the open-ended, packer-less system. The ABA with gas lift system utilizes tubing and gas lift valves above a packer and a bypass assembly through the packer to allow injected gas to pass through. Injected gas enters the assembly from the tubing/casing annulus, just above the packer, and exits to the annulus just below the packer. Production is normal up the tubing, and no adjustments are needed on the wellhead. By using this system, the operator is able to optimally produce a deviated wellbore. Where typically the deepest point of injection is just above the packer, the ultimate point of lift for an ABA system can be the end of tubing, allowing for greater flowing bottom hole pressure. This is achieved by allowing the lift gas to pass through the packer to the end of tubing once all gas lift valves have closed. No fluids re-enter the tubing/casing annulus above the packer, as the ABA is checked, taking full advantage of the packer. The ABA with gas lift system also makes it possible to treat the tubing string and casing with chemicals, by way of injection gas, both above and below the packer.
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Dip Tube
This method of deep lift utilizes a crossover flow adapter and a unique mini well bore below the packer. This assembly will facilitate the deepest point of gas injection without applying additional back pressure on the formation. A typical installation might have 2-3/8" tubing above the packer, a crossover flow adapter with 2-7/8" tail pipe below the packer and a 1" internal injection string inside the tail pipe. Compressed gas travels through the casing annulus, through the crossover flow adapter and into the 1" injection string. The gas then exits a gas lift valve and mixes with the produced fluid and gas in the 2-7/8" x 1" annulus. The fluid and gas flow up through the crossover flow adapter into the 2-3/8" production tubing and to the surface. Able to accommodate most wellbore characteristics, the Dip Tube Assembly is an efficient means of lowering the flowing bottom hole pressure beyond what is capable with conventional gas lift methods.
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Enhanced Annular Velocity System
The EAV method of gas lift utilizes tubing and gas lift valves above a packer, and a selectively sized injection string with internally mounted gas lift valves below. Injected gas flows into the casing annulus through a crossover flow adapter at the packer and into the injection string below. When the deepest point of injection is obtained, the gas exits the injection string, mixes with the produced gas and fluids and flows up the annular area. The fluid and gas flows through the crossover flow adapter and into the production tubing to the surface. Success of this system is dependent on the proper sizing of the tubing and injection string, ensuring adequate flow velocity can be maintained through the entire length of the well.
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Marathon AVE (Annular Velocity Enhancement)
Wireline Retrievable System
Once thought impossible, a wireline retrievable AVE (commonly known as EAV) system has been patented by Marathon and is exclusively sold and manufactured by PCS. This nontraditional system allows for gas injection through an injection string below the packer similar to the PCS AVE system but offers the tremendous advantage of being wireline retrievable. The entire crossover flow adapter assembly can easily be retrieved with wireline to facilitate wireline or coiled tubing work below the packer. All of the gas lift valves above and below the packer are also wireline retrievable.
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Packerless Dead String
This application can be used to prevent liquid loading in wells with long perforated intervals or horizontal laterals to ensure stable production and the lowest possible FBHP. The installation consists of production tubing and gas lift valves above a slotted crossover flow sub and a dead string below. With a properly sized dead string, the produced fluid and gas will flow with adequate velocity in the annular area through the slotted sub and into the production tubing. A traditional gas lift operation then occurs and delivers all liquids and gas to the surface.
