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Sustaining the pressure

Published by , Editorial Assistant
Oilfield Technology,


Neil Wilson, Expro, UK, outlines a new intervention system for treatment of sustained annulus pressure.

Sustaining the pressure

Sustained annulus pressure (SAP), also known as sustained casing pressure (SCP) is a growing concern for operators and duty holders constantly seeking methods to manage well integrity and new ways of innovating to increase production. Casing annuli are typically not designed for intervention and are only accessible from the casing valves at the surface. While the A annulus may have limited accessibility from the tubing itself, access for the B and C annulus is non-existent. Until recently this has been the biggest challenge in solving SAP in casings. Traditionally, it meant wells had to be shut-in or required lengthy lubricate and bleed operations or, worst case, a workover. However, a new well intervention and integrity technology has been developed for the targeted remediation of annulus integrity issues. The annulus intervention solution, called Octopoda, has been created by energy services provider Expro. It allows direct access and intervention of the annuli and is successfully supporting operators and duty holders to ensure safe and reliable production from their well stock.

Integrity, efficiency, sustainability

Three unmanned gas production wells (wells 1, 2, and 3) offshore Malaysia had a history of SAP. Initial attempts to solve the issue in wells 2 and 3 involved conventional lubricate and bleed with high-density brine. This only succeeded in reducing the pressure to just below the MAWOP limit. Wells 2 and 3 were worked over and recompleted to address SAP in the B annulus. Later, well 1 was also found to have SAP in the B annulus. The highest recorded pressure was around 500 psi, exceeding the operator guideline trigger limit of 300 psi. The recorded pressure buildup was modest at 15 psi/d, and there was no communication with other annuli. It was agreed that SAP in Well 1 could be resolved using the Octopoda annulus intervention system. Octopoda accesses the annulus to bring shut-in wells with integrity issues back to optimal production. It includes a flexible conveyance system at the annulus gate valve and can adjust its fluid delivery point to below the valve ensuring an optimal depth for fluid injection. The system includes integrated well control barriers including an emergency cutting device when rigged up to the wellhead. All ancillary equipment is compact, Zone 2 rated and/or API-compliant, and due to its small footprint can be positioned very close to the wellhead.

Well integrity assurance

The system includes a high-pressure intervention designed hose with a limited-length spiral-type tension spring attached to its lowermost end. When deployed into the annulus via the Octopoda surface package, the direction of the spring and the hose are altered from horizontal to vertical using a bending head attached to the innermost end of a pressure-tight insertion mechanism. A cutting device is integrated into the front end of the bending head, allowing the hose or spring to be cut inside the well. This allows for the retraction of the bending head from the well and the closure of the annulus gate valve in an emergency. The annulus intervention system utilises a gravity displacement and diffusive mixing technique from the depth of injection. A fundamental operating principle of the system is that a higher-density fluid is injected via the hose relative to the density of the in-situ annulus fluid. The higher-density fluid gravitates to the bottom of the annulus, with returns being taken simultaneously at surface, this process continues until the lower density in-situ annulus fluid are fully replaced. This gravity displacement and diffusive mixing technique enables the in-situ annulus contents to be swapped without the need for the annulus intervention hose to be deployed to the annulus total depth which could be thousands of feet. This system extends the boundaries of conventional intervention. It opens the possibility to intervene live annuli and maintain wells with shut-in casings pressure, corrosive fluid challenges, leakages, and more to contain or regain the integrity of producing or shut-in wells.

Field site visit

A site survey was conducted at well 1. A wellhead survey tool with a special lead impression block (LIB) was run to ensure the intervention tool could be stroked successfully into the B annulus inlet and surface accessibility was assessed to cover all operational requirements. Apart from identifying the geometry of the wellhead annulus inlet, the survey tool had a special head that enabled measurement of the casing hanger clearance. This was imperative to ensure that the following measurement was taken and confirmed. Based on the survey tool run in the wellhead, the measurement was confirmed. A 45° flute was also confirmed, enabling the tool to be engineered and modified to cater to this as opposed to the 90° angle seen on most of the wellheads. A surface evaluation was conducted as part of the site survey. An evaluation was made of the surface accessibility for the equipment rig-up as well as the return line. This was to ensure that the return could be managed accordingly during the project execution. It was found that the wellhead was accessible for entry from the active side of the wellhead. The passive side of the wellhead was obstructed by the platform structure. However, it was still accessible and was hooked up with a line for taking the return.

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Read the article online at: https://www.oilfieldtechnology.com/special-reports/31102024/sustaining-the-pressure/

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