In drilling, a hermetic test (or hermetical test) is a critical pressure test to ensure the production casing or wellbore is completely sealed, preventing fluid and pressure leaks into the formation or surface, using high pressure (often water or mud) to check for leaks in the casing, cement bond, and wellhead equipment before the well is put into production, verifying its structural integrity and safety for long-term operations.
Purpose of Hermetic Testing:
- Casing Integrity: Verifies the casing string itself hasn’t failed under pressure.
- Cement Bond: Assesses the seal between the casing and the formation rock, ensuring no micro-annulus forms.
- Wellhead Safety: Checks the integrity of the Christmas tree and surface equipment.
- Preventing Contamination: Stops unwanted fluid migration between zones or to the surface.
How It’s Done (General Process):
- Preparation: After cementing the casing, the wellbore fluid might be changed to water or a specific mud type.
- Pressurization: Pressure is gradually applied to the casing from the surface, often to high PSI (e.g., 4500-10,000 psi).
- Monitoring: The pressure is held, and the system is monitored for any pressure drops, indicating a leak.
- Confirmation: Techniques like Cement Bond Logs (CBL/VDL) might be run before and after to check the cement, and the wellhead is also pressure tested.
- Negative Test: Sometimes a “negative test” (reducing pressure) is performed after a positive test for added assurance.
Methods & Related Tests:
- Pressure Testing: The primary method, using fluid to test the sealed system.
- Leakoff Test (LOT): A pre-casing test to find formation fracture pressure, different from the casing’s hermetic test.
- Drill Stem Test (DST): A broader test to evaluate reservoir potential, which includes components of integrity testing.
Why It’s Crucial:
Failure to achieve a hermetic seal can lead to lost circulation, blowouts, environmental damage, and poor production, making this a vital step in well completion.
