Around the world, mature oil fields are a huge source of production as roughly 70% of oil production today comes from wells that are more than 30 years old. Despite many years of production, a significant amount of this oil in these mature fields remains unproduced. A 2000 study by the US Geological Survey estimates only about a third of recoverable oil has

Figure 1. In open hole, the main components of an expandable liner run include a launcher assembly that houses the expansion cone, the solid expandable liner, and an anchor hanger. The launcher is constructed of a thin wall, high-strength steel with an outside diameter compatible with the drift of the base casing. Cased-hole expandable liners employ the same components with a simple variation — an anchor-hanger joint with a series of elastomer bands outside the body immediately above the launcher serves as a seal and anchors the bottom of the system to the base casing.
been produced. These left-behind assets are in the center of an existing and already capitalized infrastructure, with wells, production systems, and gathering lines in place. The economic incentive to improve and extend production from these fields is enormous.


Armed with expandable tubulars and other technologies, operators are taking a new look at old assets. Workovers, in the past viewed as a management problem and an expense, are today seen as an opportunity. Marginal and plugged wells are being revived as significant producers and as a means to reach additional reserves.

An option to P&A

Enventure’s solid expandable technology resizes tubulars in situ through
a process that expands the steel to enlarge the pipe diameter. Pioneered by the company in the late 1990s and used initially to enhance deepwater drilling capabilities, expandables are finding broad acceptance among operators of aging assets. They are being used to address many common workover applications, from corrosion to multizone completions. The advantages are significant, and the technology is often the difference between profitability and plugging the well.

As a result, operators have quickly adopted the technology and are applying it in field-wide remediation programs with considerable success.

Maximizing reservoir potential

Expandable technology is an enabling system that improves efficiency and economics in well remediation and sidetrack projects. Its application offers a strategic approach to workovers that increases production and reserves. This is especially true in multi-well strategies where the technology is yielding significant economic benefits.

Expandable tubulars have a broad range of application in either cased- or open-hole environments. In re-fracing old and new zones, expandables provide precise isolation of perforations, with a higher pressure rating and greater longevity than cement squeezes and casing patch alternatives. And unlike scab liners, expandable casing liners conserve hole diameter so pump rates are not constrained.

The technology also effectively isolates water production. Where corrosion and damage has diminished wellbore integrity, expandable systems are a reliable, long-term means of restoring wellbore integrity.

As an enabler for side-tracking, use of rotary-steerable systems, and intelligent completions where hole diameter is critical, the technology conserves hole size and provides the working room to reach new assets and provide long-term management capabilities that optimize production. This capability is helping operators install the latest production technology in 30-year-old wells.

Field-wide revival

In two Far East onshore oil fields, abandoned wells are being returned to production in a workover program using expandable tubulars. Casing corrosion, formation stress, and unwanted perforations resulted in thousands of wells being marginal or shut-in. Using expandable tubulars in a multifield, multiwell project has resulted in an average increase per well of about 22 b/d of oil. At this rate, the installation was paid for in 30 days. Individual wells have shown improvement from 5 to more than an exponential 400 b/d of oil and from shut-in to 128 b/d of oil.

The economic potential of these wells led the operator to investigate ways to quickly resume oil production. Solid expandable tubular technology, used to repair the wells and improve production, provided an economically and technically feasible solution that could be applied at a field level.

To capitalize on the project’s scale, an efficient and economical system was developed. The solution for this project installed bull-nosed 41⁄4-in. by 51⁄2-in. cased-hole liner systems in a series of wells over three different fields. Liner lengths have ranged from 75 to 400 ft (22.8 to 122 m) with setting depths ranging from a 1,650- to 10,400-ft (503.25- to 3,172-m) range. The operator then prepared the wells in batches and coordinated workover rigs to install the expandable systems quickly and effectively. Compared with other technologies for restoring damaged oil wells, expandables simplified the process and reduced total costs. Reliability is significantly improved, with a very high project success rate
of more than 99%.

Economy of scale

Nearly 100 wells in Texas with little or no production were the target of a successful re-completion program using expandable tubulars. Production in many of these wells, including some that were plugged and abandoned or producing only 2 b/d of oil, has increased to almost 15 b/d of oil.
The treatments are paying out in just two to three months.
To re-complete the wells in a marginal field, the major independent operator planned to stimulate a new zone. Doing so required isolating perforations in old completions. In addition, an aggressive frac design required protecting very old, corroded casing from high hydraulic pressures.


Conventional cement squeezes

in the field had limited success and had proven costly. Using scab liners reduced the inside diameter and prevented pumping at the desired frac rates. However, using expandables
in a cased-hole liner application conserved hole size while providing higher burst and collapse ratios. In the first quarter of 2008, nearly 25
of the targeted 75 to 100 well candidates had been re-completed. Cased-hole liner installations ranged from 180 to 700 ft (54.9 to 213.5 m).

Optimizing investment

For one operator, expandable technology provided a solution for thief zone isolation as an alternative to costly and often ineffective workover operations. In waterflood projects, expandables’ ability to conserve internal well diameter is helping improve flood sweep efficiency for improved production and higher reserves.

Thief zones made water injection difficult to effectively manage. To control the flood, it was necessary to shut off problem perforations while leaving others open for injection. The operator, Denbury Resources, had tried squeezing, casing patches, and dual-packer isolation assemblies. But poor placement accuracy and reduction of inside wellbore diameter meant these methods were rarely effective.

To conserve internal well diameter while improving injection water distribution, Denbury initiated a multi-well program in its South Mississippi Heidelberg field — one of the company’s largest fields. Using 41⁄4-in. by 51⁄2-in. cased-hole expandable systems installed in lengths of about 40 to 80 ft (12.2 to 24.4 m), the operator is accurately isolating select thief intervals with minimal loss of inside diameter.

When two wells in close proximity required work, Enventure was able to install expandable systems across the middle zone in a single day while leaving the upper and lower perforation sets open for injection.

New profitability

The application flexibility of solid expandable technology has made it a workhorse for a broad range of well remediation techniques. While conserving hole size, it provides a reliable, accurate, and long-term solution for isolating zones and repairing casing integrity. It provides a high-pressure environment for re-fracing older wells and helps reach new assets with the hole size needed for advanced completion systems. These solutions are creating new profitability for operators of mature assets.