Gas anchors
A gas anchor separates free gas from well fluid below a sucker-rod pump, so the pump fills with liquid instead of gas locking. This page covers the four types, how to size one against your pump rate, what a quote needs from you, and where each type stops working. Maximus OIGA Private Limited builds SpectraMax gas anchors to order at its Manjusar / Savli plant in Vadodara. Lead time runs 1 to 4 weeks for dip-tube and collar-size anchors, and 4 to 12 weeks for packer-type separators.
Maximus OIGA - Gas Anchors
SpectraMax Gas Anchors, Engineered to Order SpectraMax gas anchors separate free gas from well fluid below your sucker-rod pump intake to prevent gas lock, built to your casing size and pump rate at the Manjusar / Savli GIDC plant, Vadodara. Button: Request a gas anchor quotation Engineered to order by Maximus OIGA Private Limited. Lead-time bands run 1 to 4, 4 to 12 and 8 to 16 weeks or more by product class. |
What is a gas anchor, and which well does it suit
| A gas anchor is a downhole gas and liquid separator: a perforated or slotted tubular run below a sucker-rod pump so free gas escapes up the casing annulus before well fluid enters the pump. Set the gas anchor below the perforations when the rathole allows, and use a collar-size or packer-type anchor when the pump must sit above them. |
The SLB Energy Glossary describes a gas anchor as a perforated tubular attached to the subsurface sucker-rod pump that controls the entrance of gas and helps prevent gas lock. Clegg's Southwestern Petroleum Short Course paper, "Another Look at Gas Anchors", calls the name a misnomer: the tool is a downhole gas separator, not an anchor.
A gas anchor run below the pump has one purpose. The anchor raises pump fillage and stops gas lock by letting free gas bypass the pump up the casing annulus, so the pump fills with liquid on each stroke.
Every gas anchor, whatever its build, relies on the same gravity principle to make that separation.
How does a gas anchor separate gas before it reaches the pump
A gas anchor separates gas by gravity: gas bubbles rise faster than the liquid moves down toward the dip tube, so gas leaves through the upper ports and liquid is drawn from below.
Fluid enters above On the upstroke, well fluid enters the outer barrel through ports or slots near the top of the gas anchor. | Gas rises and exits Liquid moves down around the dip tube while each gas bubble rises and leaves through the same ports into the casing annulus. | Liquid goes down to the dip tube Liquid reaches the bottom of the dip tube and flows up to the pump, as long as the downward liquid velocity stays below the bubble rise velocity. |
The dip tube, also called the mosquito bill, is the inner tube the pump draws liquid through, and it opens near the bottom of the outer barrel. The ports can be cut in a perforated nipple or a slotted barrel, and a mud anchor below lets solids settle out of the liquid.
McCoy and Podio (1998) state the governing condition: separation holds only while the downward liquid velocity in the separation annulus stays below the gas bubble rise velocity.
Each configuration of gas anchor applies this principle in a different place in the well.
What types of gas anchor are there
Gas anchors come in four main configurations: the natural gas anchor (pump set below the perforations), the poor-boy gas anchor with its dip tube, the collar-size gas separator, and the packer-type gas separator, with a mud anchor added where solids travel with the gas.
Natural gas anchor
What it is: A placement, not a tool: the pump intake sits below the perforations, so the casing itself acts as the separator.
Best when: The well has enough rathole to set the intake at least 5 ft below the fluid entry zone.
Watch for: Not an option when the pump must sit above the perforations.
Poor-boy gas anchor
What it is: A perforated or slotted outer barrel with a concentric dip tube, run below the pump, with no seal to the casing.
Best when: The pump sits above the perforations and the pump rate is low to moderate.
Watch for: The small annulus inside the barrel caps how much liquid it can separate.
Collar-size gas separator
What it is: An outer barrel as large as the tubing collar allows, with ports at the top and an internal dip tube.
Best when: The pump sits in or above the fluid entry zone and needs more capacity than a poor-boy barrel gives.
Watch for: The casing drift caps the barrel diameter.
Packer-type gas separator
What it is: A cup or packer seal on the separator mandrel, so separation happens in the larger casing annulus above the seal.
Best when: The pump rate is beyond what an internal annulus can separate.
Watch for: Solids can settle on the seal cup, and the cup must suit the well fluid and temperature.
Mud anchor add-on
What it is: A lower joint or slotted barrel that lets solids settle out alongside the gas separation.
Best when: Sand or other solids travel with the gas.
Watch for: Does not separate gas on its own; run it below one of the four configurations above.
All four types of gas anchor are built to order in the SpectraMax line, to the casing size, tubing connection and pump rate on your enquiry, with no stocked model list.
Choosing between them comes down to matching the configuration to your well condition.
Which gas anchor suits your well condition?
The right gas anchor depends on three well conditions: whether the pump can be set below the perforations, the liquid rate the pump displaces against the casing size, and whether solids or deviation are present. Each row below names the condition under which its choice stops holding.
| Well condition | Configuration | Why it fits | Where it stops |
|---|---|---|---|
| Rathole below the perforations | Natural gas anchor, with the pump intake at least 5 ft below the fluid entry zone | The casing becomes the outer barrel, which gives the largest separation area; McCoy and Podio call it the simplest and most efficient option. | Not available when the pump must sit above the perforations. |
| Pump above the perforations, low to moderate pump rate | Poor-boy gas anchor or collar-size gas separator, with the largest outer barrel the casing drift allows | Separation happens inside the barrel, with no seal to set. | Stops when pump displacement exceeds the capacity of the annulus inside the barrel. |
| Pump above the perforations, liquid rate beyond the internal annulus capacity | Packer-type gas separator | Separation moves to the larger casing annulus above the seal. | Stops when solids settle on the seal cup, or the cup does not suit the well fluid and temperature. |
| Solids travel with the gas | Add a mud anchor below the gas anchor | Solids settle out in the lower joint instead of reaching the pump. | Does not separate gas on its own; it pairs with one of the configurations above. |
| Deviated setting depth | Any configuration, with the inclination at setting depth stated on the enquiry | Gravity separation performance changes with inclination. One 2021 Southwestern Petroleum Short Course study found its own tool most efficient at about 40 to 45 degrees and cautioned against solids placement beyond 65 degrees. | Those angles are that study's findings for its own tool, not a general rule. |
Before you choose a row, confirm the well is one where gas anchors are used at all.
Where are gas anchors used, and where are they not the right tool?
Gas anchors are used in sucker-rod pumped oil wells that produce free gas at the pump intake, usually run on the same string as a tubing anchor catcher.
Used in
| Not the right tool when
|
In every well where it is used, the gas anchor answers gas interference, which starts as low fillage and fluid pound and can rise to full gas lock.
The tubing anchor catcher is the companion tool on the same string: it holds the tubing still against pump-stroke movement, while the gas anchor separates gas. SpectraMax already makes four tubing anchor catcher models, two of them built to stop tubing movement caused by pump action or gas interference.
Once the gas anchor is the right tool, the next check is whether it is big enough for your pump.
How do you size a gas anchor for your pump rate
A gas anchor's liquid capacity is set by the area of the annulus where liquid moves down, multiplied by a downward velocity of no more than 6 inches per second, which is about 53 bbl/d for every square inch of annulus.
| Capacity (bbl/d) = separation annulus area (square inches) x 53.4. The constant is 0.5 ft/s x 86,400 s/d / 5.615 cu ft per bbl / 144 square inches per sq ft. |
McCoy and Podio (1998) put the bubble rise velocity of gas in low-viscosity produced liquid (under 10 cp) at about 6 inches per second. Small bubbles rise more slowly: the 2021 Southwestern Petroleum Short Course study, citing Stokes, gives about 1 in/s for a 1/8 in bubble and about 6 in/s for a 1/2 in bubble, so treat 6 inches per second as an upper bound.
| Configuration | Annulus (sq in) | Capacity at 6 in/s (bbl/d) | Note |
|---|---|---|---|
| Natural gas anchor: 5-1/2 in 17 lb/ft casing (casing ID 4.892 in) around 2-7/8 in tubing | 12.3 | about 650 | The casing is the outer barrel. |
| Poor-boy gas anchor: 2-7/8 in barrel (ID 2.441 in) around a 1 in dip tube (OD 1.315 in) | 3.3 | about 175 | Liquid moves down inside the barrel. |
Your numbers change with casing weight and barrel size; send them and the quotation confirms the sizing.
The same well separates roughly four times more liquid when the pump can sit below the perforations.
Size against the pump displacement during the stroke, not the well's daily average, because liquid moves through the anchor while the pump is drawing. Keep friction loss through the dip tube preferably under 1/2 psi, as McCoy and Podio advise.
Those sizing figures become the dimensions a quotation has to fix.
Need expert guidance on the right solution?
Talk to our engineers about your project requirements.
What specifications define a SpectraMax gas anchor
A SpectraMax gas anchor is specified by casing size and weight, tubing and pump connection, barrel and dip tube size, length, port or slot pattern, material, and whether a seal cup or mud anchor is added.
| Parameter | What you tell us | What the quotation confirms |
|---|---|---|
| Casing size and weight | Casing OD and weight, for example 5-1/2 in, 17 lb/ft | Casing ID and drift, and the largest barrel that fits |
| Tubing and pump connection | Tubing size and thread, and the pump's bottom connection | EUE or NUE 8-round end connections, thread form per API 5B |
| Barrel size | A preferred nominal size, or none if you want the sizing check to set it | Barrel OD and ID, sized against your pump displacement |
| Dip tube size | Pump intake size | Dip tube OD and length, checked against the 1/2 psi friction guideline |
| Length | Setting depth relative to the perforations | Assembly length and port position |
| Port or slot pattern | Gas and solids load, where known | Port or slot pattern, count and position |
| Material and options (seal cup, mud anchor) | Corrosive service (H2S, CO2), solids, and whether you want a seal cup or mud anchor | Material grade on the material test report; seal cup and mud anchor specified to your conditions |
Gas anchor barrels in the market come in nominal sizes of 3/4 in, 1 in, 1-1/4 in and 1-1/2 in, with lengths between 12 in and 20 ft. SpectraMax gas anchors are built to the requested size and length across that range.
End connections are tubing threads: the tubing connection and pump connection on your order, EUE or NUE 8-round, with the thread form per API 5B.
The material is carbon or alloy steel tubular, with stainless steel for corrosive service where you specify it, and the material test report confirms the grade. For reference, one market line uses 316L stainless and Schedule 40 steel.
A gas anchor is not a pressure-sealing tool. Its limit is the body and connection strength of the tubular it is made from, and on a packer-type separator the seal cup is specified to the well conditions on your enquiry. The port pattern and length follow from your setting depth and gas load.
With the specification set, the remaining question is how a gas anchor compares with the other ways of handling gas.
How does a gas anchor compare to the alternatives
A gas anchor, compared with the alternatives, is the lowest-cost tool for keeping gas out of a sucker-rod pump; setting the pump below the perforations separates gas more efficiently where the well allows it, and cyclonic separators handle rates beyond a gravity anchor.
| Approach | How it handles gas | Best when | Limit |
|---|---|---|---|
| Natural gas anchor (pump set below the perforations) | The casing acts as the outer barrel and gas rises up the casing annulus | The rathole allows the intake at least 5 ft below the fluid entry zone | Needs rathole below the perforations |
| Poor-boy gas anchor or collar-size gas separator | Gravity separation inside a ported barrel around a dip tube | The pump sits above the perforations at a low to moderate rate | Capacity set by the annulus inside the barrel |
| Packer-type gas separator | A seal cup moves separation to the larger casing annulus | The liquid rate is beyond an internal annulus | The seal cup must suit the well fluid and solids |
| Cyclonic separator | A patented class of downhole gas separator that uses cyclonic motion and baffles | Gas and solids loads are higher than a gravity anchor handles | A different product class from the gravity designs on this page |
| Buying the gas anchor from a specialist manufacturer does not break the integrated bundle from your pump supplier. The anchor threads to the pump and tubing by the tubing connection specified on your order, and SpectraMax already supplies tubing anchor catchers for the same rod-pumped string. |
Each of these approaches has a point where it stops working.
Where does each gas anchor option stop working
Every gravity gas anchor stops working when the downward liquid velocity in its annulus exceeds the bubble rise velocity, or when gas arrives in slugs faster than the ports can vent it. Past that limit, pump fillage falls and the pump can gas lock.
Summary (visible above the panels)
- Side-intake ports: liquid entry falls off above about 6 ft/s superficial gas velocity, and the separator is starved at about 10 ft/s.
- Slug flow: in one study, gas above about 140 Mscf/d in 5-1/2 in casing gave poor or erratic pump fillage.
- Deviated and horizontal wells: separation changes with inclination, so state the angle at setting depth.
Natural gas anchor
Visible: The natural gas anchor stops working when pump displacement exceeds the casing annulus capacity, about 650 bbl/d in 5-1/2 in 17 lb/ft casing around 2-7/8 in tubing.
In panel: Gas arriving as slug flow can still overwhelm it, as the thresholds above show.
Poor-boy gas anchor or collar-size gas separator
Visible: These anchors stop working when the pump rate exceeds the capacity of the annulus inside the barrel, about 175 bbl/d for a 2-7/8 in barrel around a 1 in dip tube.
In panel: A larger barrel, where the casing drift allows, or a packer-type separator raises that limit.
Packer-type gas separator
Visible: The packer-type separator stops working when solids settle on the seal cup, or when the cup does not suit the well fluid and temperature.
In panel: The seal cup is specified to the conditions on your enquiry, which is why the quotation asks for fluid, temperature and solids data.
Side-intake ports on any configuration
Visible: Liquid entry through side-intake ports diminishes above about 6 ft/s superficial gas velocity in the adjacent casing annulus, and the separator is starved at about 10 ft/s.
In panel: These are findings of the 2021 Southwestern Petroleum Short Course study. The same study found gas rates above about 140 Mscf/d in 5-1/2 in casing likely to give poor or erratic pump fillage.
Any gravity anchor in a deviated or horizontal well
Visible: Separation in any gravity anchor changes with inclination, so the angle at setting depth belongs on your enquiry.
In panel: The 2021 Southwestern Petroleum Short Course study reports its own tool most efficient at about 40 to 45 degrees; treat that as one tool's result, not a rule for a horizontal well.
Knowing these limits, the next question is which standards cover a gas anchor at all.
Which standards apply to a gas anchor, and how do you verify a vendor's claims
A gas anchor is not covered by a product specification of its own: API 11AX covers the sucker-rod pump and its standard fittings and excludes specialty accessories, so a gas anchor is specified by its connections, material and dimensions.
The scope of API 11AX is subsurface sucker-rod pump assemblies (insert and tubing), their components and fittings; it excludes specialty subsurface sucker-rod pump accessories and special-design components. The thread form of a gas anchor's end connections follows API 5B.
When a listing sells an "API gas anchor", ask which API document it means: the connection thread form, the pump the anchor hangs from, or a company quality licence. Then verify it in four steps.
- Name the document. Ask which API standard the claim refers to, and check that its scope covers the product in front of you.
- Get the licence number. A licence has a number and names the specification it covers.
- Search the register by exact legal name. Open the API Composite List at mycerts.api.org, search the vendor's exact legal name, and read the status and the specification. Only ACTIVE is current.
- Record the date. Note the date you checked, because a licence status can change.
The same check applies to every vendor, Maximus OIGA Private Limited included. For the part itself, the stronger evidence is the paper that travels with it: a material test report traceable to a heat number, and the inspection record for its connections.
Those documents, rather than a badge, are what should travel with the order.
What documentation ships with a SpectraMax gas anchor
Each SpectraMax gas anchor order ships with a dimensional drawing, material test reports traceable to heat numbers, a thread inspection record for the end connections, and a certificate of conformity to the purchase-order specification.
Drawing A dimensional drawing of the assembly as built to your order. | MTR with heat numbers Material test reports (MTR) traceable to the heat number of each tubular. | Connection inspection record A thread inspection record for the end connections, against the thread form on the order. | Certificate of conformity A certificate of conformity to the specification on your purchase order. |
An inspection and test plan (ITP) is issued with the order when your QA team asks to review it before manufacture.
That documentation pack ships within the lead-time band for your configuration.
Section 13 of 16 | ADD | Placement: After "What documentation ships with a SpectraMax gas anchor?" | Zone: body | Component: proof-strip
What is the lead time for a SpectraMax gas anchor
SpectraMax lead-time bands by product class run 1 to 4 weeks, 4 to 12 weeks, and 8 to 16 weeks or more. Dip-tube and collar-size gas anchors sit in the 1 to 4 week band, packer-type gas separators with a seal cup sit in the 4 to 12 week band, and the quotation confirms the band for your configuration.
1 to 4 weeks Shortest band. Poor-boy (dip-tube) and collar-size gas anchors sit here. | 4 to 12 weeks Middle band. Packer-type gas separators with a seal cup sit here. | 8 to 16+ weeks Longest band, for other SpectraMax product classes. |
Every SpectraMax gas anchor is engineered to order by Maximus OIGA Private Limited. None of the gas anchor sellers checked on September 25, 2026 published a lead time; this page states the lead-time band so you can plan the job before you ask.
The lead time covers the gas anchor itself; what this page and this supplier do not cover comes next.
What does this page not cover?
Maximus OIGA Private Limited does not supply the sucker-rod pump, the rods, the pumping unit, or rig-site installation and troubleshooting with a gas anchor; it manufactures the gas anchor to your specification and ships it with its documentation.
- We do not supply the sucker-rod pump, the rods or the pumping unit; your pump supplier provides those.
- We do not send rig-site personnel for installation or troubleshooting.
- This page does not cover ESP rotary gas separators or surface production separators.
- This page makes no API licence claim, states no pressure or temperature rating and gives no installation count. The verification steps and the documentation pack cover that ground by letting you check the part itself.
That leaves the questions engineers still ask about gas anchors.
Gas anchor questions engineers ask
What is the purpose of a gas separator?
A downhole gas separator keeps free gas out of the pump so the pump barrel fills with liquid. In a rod-pumped well the gas anchor does this job, sending gas up the casing annulus and liquid to the pump through the dip tube.
What is a gas-locked pump?
A gas-locked pump is a rod pump whose barrel is full of compressed gas, so the valves do not open and the pump moves no liquid. A gas anchor below the pump prevents gas lock by separating the gas before it enters.
What is a tubing anchor?
A tubing anchor holds the tubing still against pump strokes, which makes it a different tool from a gas anchor despite the shared name. SpectraMax makes both: tubing anchor catchers and gas anchors for the same rod-pumped string.
Is a gas anchor the same as a downhole gas separator?
Yes, in function: a gas anchor is a downhole gas separator, and the name is historical. Clegg's Southwestern Petroleum Short Course paper calls the name a misnomer for that reason.
Where should a gas anchor be set relative to the perforations?
Set a gas anchor below the perforations where the rathole allows, with the pump intake at least 5 ft below the fluid entry zone. Where the pump must sit above them, use a poor-boy, collar-size or packer-type gas anchor sized to your pump rate.
If I buy the gas anchor from a specialist manufacturer, do I lose the integrated bundle?
No, because a gas anchor threads to the pump and tubing by the standard connection specified on your order, so it fits the string your pump supplier provides. SpectraMax also supplies tubing anchor catchers for the same string.
What should a gas anchor quotation specify?
A gas anchor quotation should specify casing size and weight, tubing and pump connection, pump size and stroke rate, setting depth relative to the perforations, inclination, solids, and the documentation you need. Maximus OIGA Private Limited confirms dimensions, connection and lead-time band on the quotation, and the engineer who reviewed this page is named below with the sources behind each answer.
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