Purpose of Vacuum Degasser in Drilling: Why Gas Removal Is Critical for Rig Safety and Efficiency

In any drilling operation, maintaining consistent drilling fluid properties is essential. However, when formation gases invade the mud system, even small amounts of entrained gas can cause major problems. The equipment specifically designed to solve this issue is the vacuum degasser. But what exactly is its purpose? Why is it so important that most modern drilling rigs include one? This article provides a standalone, in‑depth explanation of the purpose of a vacuum degasser in drilling, the problems it solves, and why AIPU Solid Control vacuum degassers are the trusted choice for operators worldwide.

1. The Core Purpose: Removing Entrained Gas from Drilling Fluid

The primary purpose of a vacuum degasser is simple but vital: to remove entrained and dissolved gases from drilling mud. Entrained gases are small bubbles that become trapped in the mud during circulation. Dissolved gases are those that have actually mixed at the molecular level with the liquid. Both types lower mud density, damage equipment, and create safety hazards. A vacuum degasser restores the mud to a gas‑free condition so it can perform its intended functions.

Without a degasser, gas‑cut mud would continue to circulate, reducing hydrostatic pressure, causing pump cavitation, and potentially leading to a blowout.

2. Secondary Purposes: What a Vacuum Degasser Accomplishes

Beyond the basic gas‑removal function, a vacuum degasser serves several critical purposes that directly impact drilling performance and cost.

2.1 Restoring Mud Density (Hydrostatic Pressure)

The most immediate effect of entrained gas is a reduction in mud density. Even 2–3% gas by volume can lower density by 0.05–0.10 SG. This reduces the hydrostatic pressure exerted against the formation. If the pressure falls below formation pore pressure, formation fluids (oil, gas, water) can flow into the wellbore – a kick. A vacuum degasser removes the gas, restoring the original mud weight and the safety margin against kicks.

2.2 Preventing Mud Pump Cavitation and Damage

Mud pumps are positive‑displacement pumps that do not tolerate gas. When gas bubbles enter a mud pump cylinder, they collapse violently under compression. This cavitation erodes piston liners, damages valves, and can break pump parts. A vacuum degasser removes gas before the mud reaches the pump suction, eliminating cavitation and extending pump life. Field data shows that pump liner life can double when a degasser is used properly.

2.3 Improving Downstream Solids Control Efficiency

After the degasser, mud normally flows to desanders, desilters, and centrifuges. These hydrocyclone and centrifuge devices rely on the density difference between solids and liquid. Entrained gas lowers the effective liquid density, reducing separation efficiency. Degassed mud allows desanders and desilters to operate at their designed performance, removing more solids and reducing wear on downstream equipment.

2.4 Protecting Rig Personnel from Toxic Gases

Formation gases often include hydrogen sulfide (H₂S), a highly toxic and corrosive gas. Even low concentrations can be fatal. A vacuum degasser extracts H₂S from the mud and directs it through a vent line to a flare ignitor (such as AIPU’s APFI series), where it is safely burned. Without degassing, H₂S could escape from the mud at the shakers or in the mud pits, endangering the crew.

2.5 Enabling Accurate Flow Measurements

Gas bubbles interfere with Coriolis and ultrasonic flow meters, causing erratic readings. This makes it difficult to balance inflow vs. outflow – a key well control indicator. By removing gas, the degasser allows accurate flow monitoring, helping detect kicks early.

2.6 Reducing Environmental Impact

When mud is discharged (e.g., in offshore cuttings injection or land farming), entrained gas can cause foaming, handling problems, and increased volatile organic compound (VOC) emissions. Degassed mud is easier to handle and less harmful to the environment.

3. What a Vacuum Degasser Does NOT Do

To avoid confusion, it is equally important to understand what a vacuum degasser is not intended for:

• It does not handle large‑volume gas kicks – that is the job of a mud gas separator (MGS).

• It does not remove solids – that is the job of shakers, desanders, desilters, and centrifuges.

• It does not mix or add chemicals – that is the job of jet hoppers and shearing pumps.

The vacuum degasser is a polishing device for continuous gas removal during normal circulation.

4. How a Vacuum Degasser Achieves These Purposes – Brief Mechanism

Understanding the mechanism helps appreciate the purpose. A vacuum degasser:

1. Creates a partial vacuum (-0.02 to -0.04 MPa) inside a sealed vessel.

2. Spreads incoming mud into a thin film (using a rotor or baffles).

3. Under vacuum, dissolved gas comes out of solution and entrained bubbles expand.

4. A vacuum pump sucks the released gas out through a vent line.

5. Degassed mud exits the vessel and returns to the mud tank.

This simple but powerful process achieves ≥95% gas removal efficiency.

5. Key Specifications – AIPU Vacuum Degassers Serving These Purposes

AIPU Solid Control manufactures vacuum degassers designed specifically to fulfill all the purposes described above. Here are two representative series.

AIPU APLCQ300 – Vertical Centrifugal Degasser

AIPU APZCQ Series – Tank‑Mounted Degassers