Stage Cementing Collars
A stage cementing collar — also called a DV (differential valve) tool or stage tool — is installed in the casing string at a predetermined depth to enable a two-stage or multi-stage cement job. It allows the upper stage of the cement job to be pumped through ports in the collar rather than up from the shoe, reducing the hydrostatic load on the formation below and allowing cement to be placed at higher levels in the annulus than would be possible in a single-stage operation.
Why Multi-Stage Cementing Is Used
In a standard single-stage cement job, all cement is pumped through the float shoe and travels up the entire annulus. In a long casing string or a well with weak formations, this creates problems:
- High equivalent circulating density (ECD) — the hydrostatic pressure of the cement column can exceed the fracture gradient of weak formations, causing lost circulation and incomplete cement placement
- Long pumping times — cement may begin to set before the job is complete in very long strings
- Inability to reach top of cement — in very deep wells, it may not be possible to pump sufficient cement to reach the required top of cement (TOC)
A stage collar divides the cement job into two stages — first stage from shoe to collar, second stage from collar upward — reducing the hydrostatic load and allowing cement to reach the required TOC.
How a Stage Collar Works
The stage collar is made up in the casing string at the required depth. During the first stage, the collar ports are closed and cement is pumped normally from the shoe. After first-stage displacement, an opening plug is dropped and pumped to the collar, opening the circulation ports. The second stage of cement is then pumped through the ports and up the annulus above the collar. A closing plug then closes the ports, sealing the second-stage cement in place.
Product Range — Vulcan PHAZE-LOK™
The Vulcan PHAZE-LOK™ stage cementing collar is available for all standard casing sizes and is designed for reliable operation in both vertical and deviated wells. The PHAZE-LOK™ system uses a mechanical locking mechanism to ensure the collar ports remain securely open during second-stage pumping and positively close after the closing plug lands.
Available in single-stage and multi-stage configurations. Contact Proxima for PHAZE-LOK™ specifications, available sizes, and pressure ratings for your cementing programme.
Key Specifications
| Parameter | Details |
|---|---|
| — | — |
| Casing sizes | 4½” – 20″ |
| Stage configuration | Two-stage standard; multi-stage on request |
| Port opening | Plug-activated mechanical system |
| Port closing | Closing plug — positive mechanical lock |
| Compatibility | Integrates with Vulcan float equipment and centralisers |
| Standard | API |
Why Source Through Proxima
Proxima supplies Vulcan PHAZE-LOK™ stage cementing collars as part of a complete Vulcan casing running and cementing package — matched to your casing programme, cementing design, and wellbore conditions.
Frequently Asked Questions
Q: Where in the casing string is the stage collar placed?
The placement depth is determined by the cementing design — typically at or near the top of the first-stage cement. The cementing engineer calculates the depth based on the required TOC for each stage and the formation fracture gradient profile.
Q: Can a stage collar be used in a deviated well?
Yes. The PHAZE-LOK™ is designed for use in both vertical and deviated wells. Confirm your well deviation profile with Proxima when specifying the tool.
Q: What happens if the closing plug does not seat properly?
The PHAZE-LOK™ positive lock mechanism is designed to prevent this — the collar remains open during pumping and locks closed when the closing plug lands. In the event of a seating failure, the collar can be sealed from inside the casing using a cement retainer or bridge plug above the collar depth.
Q: Can Proxima supply the complete cementing tool package — float equipment, centralisers, and stage collar?
Yes. Proxima supplies complete Vulcan casing running and cementing packages from a single order, with all tools sized and matched to your casing programme.
