Cased Hole Completions System Safety – Part 2

The quality of a cementing job is vital to the safety, efficiency and cost effectiveness of deepwater well. Yet, well casings can be made even safer by the addition of a barrier in the annulus between casings. Offshore service providers have developed a variety of ways to create this extra barrier.

Baker Hughes has developed its version of a secondary mechanical pressure barrier above the uppermost hydrocarbon zone, designed to prevent any unintended and uncontrolled flow of reservoir fluids to surface in the event of failure of the cement barrier, and also help boost production rates by eliminating flow that would otherwise be lost to the annulus (if positioned in the B-Annulus*). Their solution is an electronically actuated packer with proven zero-extrusion gap seal technology. Named Cytadel packer, it is designed to provide a gas-tight annular seal for the life of the well.

The packer has 3 fundamental components:

1- A downhole packer, built from a solid-body mandrel with tubular connections. With no flow paths through the body, the packer maintains pressure integrity and eliminates the potential for hydrocarbon communication between the casing and the annulus. The body also matches the burst and collapse properties of the casing, thus helping to ensure wellbore integrity, which is vital.

2- A seal based on Baker Hughes’s ZX technology. The zero-extrusion gap seal has been qualified to ISO 14310/API 11D1 V0 pressure acceptance criterion of up to 15,000-psi differential at temperatures of up to 400°F (204°C).

3- A modular electronic trigger mechanism, which is deployed and activated in one trip and eliminates the need for pressure or pipe manipulation to set the packer.

The system, which is typically installed as part of a long-string casing string, helps increase safety by curtailing issues associated with both annular casing pressure (ACP) and sustained casing pressure (SCP). It’s important to note that ACP builds in or between the tubing and casing strings as the fluid heats up during its production up the well. The V0-rated seal created by the mechanical packer prevents this pressure from traveling to upper casing strings. This provides an additional level of safety assurance and prevents casing collapse, particularly for those wells where bleed-off equipment is not installed at the wellhead. Unlike ACP, SCP builds back up in or between the tubing and casing strings after being bled down at the surface, representing an direct safety hazard.

* B-Annulus - The annulus designation between the production casing and next outer casing. The letter designation continues in sequence for each and every outer annular space encountered between casing strings up to and including the surface casing and conductor casing strings.

Source: Baker Hughes, Drilling Contractor, IADC