What Is a Vacuum Degasser? Essential Guide to Gas Removal in Drilling Fluids

In oil and gas drilling operations, the presence of entrained gases in drilling fluid is a serious safety and performance hazard. Gases such as methane, hydrogen sulfide (H₂S), and carbon dioxide can enter the mud system from the formation. If not removed, these gases reduce mud density, cause pump cavitation, and create the risk of a blowout. The equipment designed to solve this problem is the vacuum degasser. This article explains what a vacuum degasser is, how it works, why it is critical for safe drilling, and why AIPU Solid Control manufactures some of the most reliable vacuum degassers in the industry.

1. What Is a Vacuum Degasser? – Definition

A vacuum degasser is a specialized vessel used in the solids control system to remove entrained gases (small bubbles) from drilling fluid. It operates by creating a partial vacuum inside a tank, which causes dissolved and entrained gases to expand, break out of the liquid, and be drawn away by a vacuum pump. The degassed mud is then returned to the mud tank for recirculation.

Unlike atmospheric degassers that rely on gravity and baffles, a vacuum degasser actively pulls gas out of the mud, achieving much higher removal efficiency – typically 95% or more.

2. Why Is a Vacuum Degasser Essential in Drilling?

When drilling through permeable formations, gases can enter the wellbore and become trapped in the drilling fluid. Even small amounts of entrained gas cause several problems:

• Reduced mud density – Gas bubbles lower the hydrostatic pressure, increasing the risk of a kick or blowout.

• Pump cavitation – Gas bubbles collapse inside mud pumps, damaging pistons, liners, and valves.

• Erratic flow readings – Gas in the mud affects flow meters and level sensors.

• Formation damage – Gas can invade permeable zones and reduce production.

• Safety hazard – Toxic gases like H₂S can escape during circulation, endangering rig personnel.

A vacuum degasser removes these gases efficiently, restoring mud weight, stabilizing pump performance, and ensuring a safe drilling environment.

3. How Does a Vacuum Degasser Work? – Step by Step

The working principle of a vacuum degasser is based on creating a low-pressure zone that causes gas bubbles to expand and separate from the liquid.

Step 1 – Mud Inlet

Gas-cut mud enters the degasser through a large inlet (typically 20″ diameter on AIPU APLCQ300 model) and is directed onto a series of baffles or a rotating distributor.

Step 2 – Vacuum Creation

A vacuum pump (or the main motor creating a vacuum effect) reduces the pressure inside the degasser vessel to -0.02 to -0.04 MPa (below atmospheric pressure). Under this partial vacuum, gas bubbles expand rapidly – a small bubble at atmospheric pressure can grow many times larger in a vacuum, making it easier to separate.

Step 3 – Gas Release and Suction

The expanded gas is drawn upward by the vacuum pump and discharged through a vent line (typically 1‑1/2″ to 2″ diameter). For flammable or toxic gases, the vent line is connected to a flare ignitor or safe disposal system.

Step 4 – Degassed Mud Discharge

The gas-free mud falls to the bottom of the vessel and is discharged through an outlet (typically 6″ diameter). A centrifugal pump or gravity flow returns the clean mud to the mud tank.

Step 5 – Continuous Operation

The process is continuous. As long as the vacuum pump and inlet flow are maintained, the degasser removes gas from the mud stream.

4. Types of Vacuum Degassers

4.1 Centrifugal (Vertical) Vacuum Degasser

• Examples: AIPU APLCQ series (APLCQ300)

• Uses a high-speed motor and a vortex or centrifugal action to spread mud into a thin film, maximizing gas release under vacuum.

• Advantages: High efficiency, compact design, no internal moving parts in contact with mud (except the impeller).

• Typical capacity: 300 m³/h (APLCQ300)

4.2 Float-Controlled Vacuum Degasser

• Examples: AIPU APVD series

• Uses an internal float valve to maintain constant liquid level inside the degasser.

• Advantages: Low power consumption, simple operation, environmentally friendly.

• Best for: Applications where energy efficiency is prioritized.

4.3 Tank-Mounted (Horizontal) Vacuum Degasser

• Examples: AIPU APZCQ series

• Mounted directly on the mud tank, with larger capacities.

• Capacities: 240 to 360 m³/h

5. Key Components of a Vacuum Degasser

6. Technical Specifications – AIPU Vacuum Degassers

AIPU Solid Control offers several vacuum degasser models to match different rig sizes and mud flow rates.

AIPU APLCQ300 – Vertical Centrifugal Degasser

AIPU APZCQ Series – Tank-Mounted Degassers

AIPU APVD Series – Float-Controlled Degasser

• High performance with low power consumption.

• Internal level float control valve for automatic operation.

• Simple, effective, and environmentally friendly.

7. Applications of Vacuum Degassers

Vacuum degassers are used in:

• Oil and gas drilling – Primary application, installed after shale shakers as the second-stage solids control equipment.

• Geothermal drilling – Where formation gases are common.

• Coal bed methane (CBM) drilling – Methane entrainment is a constant issue.

• H₂S (sour gas) fields – Special H₂S‑resistant steel construction is required to prevent corrosion and hydrogen embrittlement. AIPU offers H₂S‑resistant materials as an option.

• Waste mud treatment – Degassing before centrifuge or filter press operation.

8. Vacuum Degasser vs. Atmospheric Degasser – Key Differences

9. Why Choose AIPU Vacuum Degassers?

AIPU Solid Control has over 20 years of experience and has delivered equipment to more than 30 countries, with cumulative shipments exceeding 300 system‑equivalent products. AIPU vacuum degassers are designed and manufactured in strict accordance with API standards and HSE requirements.

Key Advantages of AIPU Vacuum Degassers:

✅ High degassing efficiency – ≥95% gas removal, restoring mud density quickly.
✅ Large capacity – Models from 240 to 360 m³/h, with APLCQ300 handling 300 m³/h.
✅ Robust construction – Heavy‑duty carbon steel or optional H₂S‑resistant steel for sour service.
✅ Compact design – Vertical degassers (APLCQ300) save valuable rig space.
✅ Advanced sealing – Comprehensive mechanical sealing technology for reliable operation.
✅ Flexible customization – ATEX, IECEX certifications; custom voltages (380V/50Hz, 460V/60Hz); any surface color.
✅ Easy maintenance – Simple internal structure, fewer spare parts.

10. How to Select the Right Vacuum Degasser for Your Rig

Consider these factors:

1. Mud flow rate – Match the degasser’s capacity to your mud pump output. AIPU offers 240–360 m³/h.

2. Gas content – For heavily gas‑cut mud, choose a centrifugal type (APLCQ or APZCQ) with ≥95% efficiency.

3. H₂S risk – If sour gas is expected, specify H₂S‑resistant steel construction – available from AIPU.

4. Space constraints – Vertical degassers (APLCQ) have a small footprint.

5. Power availability – Ensure your rig’s electrical system matches the motor requirements (customizable).

11. Common Misconceptions About Vacuum Degassers

❌ “A mud gas separator can replace a vacuum degasser.”
False. A mud gas separator removes large free gas bubbles at the flowline, but cannot remove small entrained bubbles. A vacuum degasser is needed for fine bubble removal.

❌ “Vacuum degassers are only for weighted mud.”
Incorrect. They work effectively with water‑based, oil‑based, and synthetic‑based muds of any density.

❌ “Atmospheric degassers are just as good.”
Not true. Vacuum degassers achieve 95%+ efficiency, while atmospheric units typically achieve 70–85%.

12. Operational Tips for Vacuum Degassers

• Position correctly – Install the degasser after the shale shaker and before the desander/desilter to remove gas before fine solids separation.

• Maintain vacuum level – Check vacuum pump performance regularly. Target vacuum: -0.02 to -0.04 MPa.

• Inspect seals – Vacuum degassers rely on good seals; any air leak reduces efficiency.

• Clean the vessel – Periodically remove any accumulated solids or scale.

• Monitor discharge – Ensure degassed mud is returned to the tank without splashing (which could re‑entrain air).

13. Conclusion: The Vacuum Degasser Is Your Safety and Efficiency Device

What is a vacuum degasser? It is a vital piece of safety and process equipment that removes entrained gases from drilling fluid with over 95% efficiency. By restoring mud density, preventing pump cavitation, and mitigating gas hazards, a vacuum degasser enables safer and more efficient drilling.

AIPU Solid Control offers a complete range of vacuum degassers – from the vertical APLCQ300 to the tank‑mounted APZCQ series and the energy‑efficient APVD series. All are built to API standards, with options for H₂S service, ATEX certification, and custom electrical systems.

When you need to get gas out of your mud, trust AIPU – your partner in solids control excellence.