Primary cementing(liner) is a well completion operation that involves placing a cement sheath around a liner string in a wellbore.
The primary cementing process for liners typically involves the following steps:
- Mud circulation: Continuously circulate drilling mud through the wellbore to remove cuttings, maintain wellbore pressure, and cool the drill bit.
- Pressure test: Verify the integrity of the wellbore and liner by conducting pressure tests, such as a leak-off test (LOT) or formation integrity test (FIT).
- Pumping wash: Displace the drilling mud in the annulus with a spacer fluid (e.g., water or brine) to prepare the wellbore for cement placement. The spacer fluid’s properties are carefully chosen to condition the wellbore walls and enhance cement bonding.
- Pumping slurry: Pump the primary cement slurry down the drill pipe and into the top of the liner. The cement slurry is specifically designed for the wellbore conditions, incorporating appropriate thickening agents, retarders, and other additives to control its setting time, density, and other crucial properties.
- Drop dart: Release a drop dart, a small mechanical device, down the drill pipe. The dart’s function is to activate a setting mechanism in the liner top packer, isolating the liner from the wellbore above.
- Displacement: Continue pumping cement slurry until it displaces the spacer fluid in the entire annulus between the liner and the formation.
- Bleed off: Allow excess cement slurry to flow back to the surface to control surface pressure and prevent potential damage to wellhead equipment.
- Setting tool released from packer: Activate the mechanism to release the setting tool from the liner top packer, signifying the completion of cement placement.
- Reverse circulate: Optionally, circulate clean fluid in the reverse direction from the annulus up the wellbore to remove any residual cement left behind, depending on wellbore conditions and operator practices.