Eliminating unacceptable levels of nonproductive time (NPT) associated with retrievable bridge plug operations is vital in well interventions at any depth. This is especially true in deepwater wells where increased cost and complex logistics put operational efficiency at center stage.

Historically, retrievable bridge plugs were designed to meet individual manufacturers’ standards, which led to widely varied performance and gave rise to inconsistent levels of NPT during interventions.

As costs associated with every facet of E&P continue to escalate, there is a need to cut money lost through NPT resulting from unreliable bridge plug operations.

Rising to the standard

In an effort to improve operational efficiency, a major North Sea operator decided to introduce ISO 14310 qualification testing as a minimum standard for its projects using retrievable bridge plugs. This action prompted vendors, led by Interwell, to qualify their plugs to the most stringent testing regime.

The ISO standard was developed to enhance the reliability of isolation barriers, including retrievable bridge plugs with a range of validation grades, providing improved clarity and assurance for the operating company. The different validation grades set test criteria and minimum quality assurance specifications, which typically require pressure and temperature cycling with defined maximum leak rates. Successful installation and retrieval are an integral part of the acceptance criteria.

The ultra-slim HP bridge plug was designed to provide a reliable barrier in extremely high-pressure conditions. (Images courtesy of Interwell Ltd.)

Most plug manufacturers found it extremely difficult to qualify their existing plugs to this new standard.

This was part of the impetus for Interwell’s designing a new range of plugs to meet the exacting standard, incorporating features that enhanced plug component integrity and reliability. The design features are intended to make the new plugs more operationally efficient. As a base standard, each plug should take one run to set and one to retrieve it.

Size matters during interventions, and Interwell’s design team focused on the need to ensure that the products were as slim as possible, which greatly increases the likelihood that they can be delivered reliably to the desired depth and retrieved through the wellbore.

The ongoing development of standards has been driven by operators as they strive to improve the reliability and integrity of wellbore barriers, which are of critical importance in deepwater and HP/HT applications, where failures can result in more complex and time consuming recovery.

Increasingly, operators demand that equipment is qualified to an industry standard, and new ratings continue to emerge, including API 11D1, which allows for monogramming of plugs to further assure quality and status.

An aging well stock brings with it increasing uncertainty on potential wellbore restrictions during intervention operations. This uncertainty can be mitigated by minimizing the diameter of bridge plug equipment. Typically, this would result in a compromise on the plug pressure and temperature rating; however, Interwell applied its patented element support technology to overcome the challenge.

Creating a solution

The 3.5-in. OD retrievable mechanical plugs were designed to be set inside 7-in. liners, and 2.8-in. OD plugs have been placed and tested successfully inside 5.5-in. tubing, both of which were qualified to the ISO 14310 standard.

The company has continued to refine and further develop HP/HT bridge plugs, which are tailored to satisfy the most common completion and liner sizes used in deepwater wells worldwide and can operate in temperatures to 200°C (392°F) and up to 15,000 psi.

Interwell unveiled the world’s first high-pressure (HP) retrievable bridge plug capable of withstanding a differential pressure of 15,000 psi at the Offshore Europe conference in Aberdeen in September 2011.

The ultra-slim, 2.2-in. OD HP bridge plug was designed to provide a reliable barrier in extremely high-pressure conditions. The ISO 14310 qualified tool contains an innovative packer backup design that both compresses and constrains the element, reducing the risk of extrusion in extreme conditions and enabling operation to 15,000 psi. The ultra-slim design reduces the risk of deployment and retrieval through narrow wellbore restrictions, a crucial operational benefit in HP/HT wells.

With a range of plug sizes for 3 1/2 in. to 7 5/8 in. casings, the ultra slim HP/HT plug design is a barrier solution for wellbores with any form of restriction, allowing it to be deployed reliably to the desired depth.

The plugs have been designed for use as both shallow and deep barriers, making them ideally suited to workover applications. They also can be used to anchor injection valves and equalization devices.

The tool can be run on slickline, e-line, coiled tubing, or pipe and features a scale tolerant slip design ensuring that it adequately grips the casing. Interwell has in-house testing facilities where plugs and packers can be qualified to the ISO 14310 V0 standard.

Reliability and quality assurance are the cornerstones of all intervention technology. Delivering plugs to ISO and API’s rigorous standards requires consistent testing. The company presently runs 500 plugs each year, often in challenging well environments, and has carried out more than 100 ISO tests to deliver to those standards.

The ISO 14310 qualified tool contains an innovative packer backup design that both compresses and constrains the element, reducing the risk of extrusion in extreme conditions and enabling operation to 15,000 psi.

Setting the bar higher

The challenge for the industry is to embrace the opportunity presented by Interwell’s field proven high expansion barrier technologies. Through operating company participation and support of R&D, there is an opportunity to create the next generation of ultra HP/HT barriers that goes beyond 15,000 psi and 200°C.

Vendors should recognize the need to tailor and qualify products for deepwater interventions with a focus on the individual requirements of the operator and its asset. When responding to bespoke design challenges, often with short lead times, it is still important to satisfy the qualification standards which aim to ensure the plug design is fit for purpose.

Well isolation challenges in deep water can be met only through rigorous qualification testing and tailoring of existing technologies to meet exact well specifications. When international standards are applied, operators will benefit from an increase in integrity assurance and reduced NPT.

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