Prolonging the economic lives of producing oil and gas wells by adapting well designs to better fit evolving reservoir conditions or solve downhole mechanical problems has been a production management and field development staple for many decades.

For most of that time, however, the high cost of deploying a rig to the well site combined with income lost as a result of production being shut in during well workovers, recompletions, repairs, or retrofits significantly limited opportunities in which the value of incremental reserves to be recovered was great enough to make the effort worthwhile.

The introduction almost 20 years ago of retrievable intervention tools that could be placed by wireline service crews at any point(s) desired in tubular and casing strings enabled producers and oilfield service companies to begin rethinking well designs, as well as remediation strategies. Eliminating the need to deploy a drilling rig to work over or retrofit an ailing oil or gas well drastically lowered the cost of well remediation, greatly increasing the number of wells for which timely, intelligent intervention made economic sense.

More affordable well-maintenance and -remediation technology encouraged engineers to begin designing production strings with no dedicated landing nipples, save one for the subsurface safety valve. The fewer obstructions the better for downhole devices meant to be inserted into and removed from the wellbore at will.

Lower costs, together with the flexibility to position intervention equipment at any point in the production string—for whatever duration was prescribed—and eliminating the necessity to kill the well during remediation procedures significantly expanded the range of circumstances in which intervention could meaningfully increase ultimate recovery.

Responding to growing challenges
Over time, the ability to prolong the economic lives of oil and gas wells without resorting to workovers and other costly remedial procedures at the well site has become increasingly important as primary well construction costs have increased. At the same time, evermore complex well designs and more difficult downhole environments—including more directional drilling, more deviated/horizontal well bores, as well as attempts to penetrate and produce from deeper, hotter, more highly pressured reservoirs—have combined to continually challenge well intervention capabilities.

Intervention product and service providers have responded by continually upgrading the capabilities of available retrievable intervention tools and by significantly expanding the types and applications of retrievable bridge plugs, packers, straddle packers, and zonal isolation plugs available in the field. As a result, oil and gas producers today may choose from a wide array of retrievable downhole devices and tool configurations to place high-pressure seals at any point in the well to solve a long list of production problems, any one of which can lead to early well shut-in, plugging and abandonment.

Until recently, the global availability of front-line intervention technology incorporating retrievable downhole equipment has been spotty, with little or no capability in some regions to mobilize the necessary manufacturing capacity quickly enough to avoid long, costly delays at the wellsite. Within the past year, however, the completion and intervention business unit of Halliburton Energy Services has begun offering its broad line of custom-engineered retrievable through-tubing intervention products and services—previously available only in the North Sea and parts of Asia—to regional Halliburton offices in major oil and gas provinces around the world.

The global strategy enables oil and gas producers—for the first time in many parts of the world—to use retrievable intervention strategies to solve problems arising from deteriorating reservoir conditions or mechanical failures, quickly and more economically than would be possible with conventional permanent packers, plugs, or straddles. Key locations have been targeted throughout the world in a strategic commitment to promote the intervention products globally.

Modern intervention capabilities
Most Halliburton custom retrievable through-tubing intervention solutions can be run and retrieved via slickline, electric line, coiled tubing or work strings for an almost limitless list of applications, such as well abandonment or suspension, leak or zonal isolation, introduction of new gas-lift points in the wellbore, or deployment of a wide range of downhole well accessories including sand control equipment. Through-tubing intervention is especially beneficial in monobore wells, which allow the use of full-bore tools for logging, perforating, and stimulating, as well as for repairing or retrofitting wells.

A key enabler in the campaign to introduce state-of-the-art retrievable intervention technology into new parts of the world has been the Halliburton downhole power unit, a non-explosive device equipped with an integral pump that generates a measured, linear force to set the company's line of retrievable plugs and packers.

By eliminating the need to detonate an explosive charge to set downhole intervention tools, the battery-powered, electro-mechanical downhole power unit allows retrievable intervention solutions to be applied in countries that ban or restrict the import or possession of explosives or igniters as domestic security measures.

The downhole power unit can be combined with a new zonal isolation plug (ZIP) in wells with  production strings of variable diameters to prevent cross-flow between production zones or to reduce water production by isolating lower production zones with high water cuts from production from higher intervals. The ZIP is a mechanical device designed to provide a high-pressure seal superior to inflatable packers or plugs. It can pass through tubing as small as 4-1/2 inches in diameter before being set in a production liner as great as 7 inches in diameter lower in the well.

Equalizing Retrievable Bridge Plug
Halliburton's premium equalizing retrievable bridge plug (RBP) can provide a high-pressure, sealed barrier anywhere in a tubing or casing string ranging in size from 2-3/8 inches to 13-3/8 inches, and can be modified to work as a one-way check valve or gauge hanger. It is designed for deployment in essentially any type of well, including vertical or horizontal well bores or oil, gas or water wells, and it is effective in some sizes in pressure regimes of up to 10,000 psi and temperatures as great as 350 degrees Fahrenheit.

Applications of the RBP are diverse and include tubing tests, setting completion packers, suspending or temporarily abandoning wells, isolating lower production zones, removing wellheads, and hanging pressure and temperature gauges. Like most of the retrievable products and services available from Halliburton's completions and intervention business unit, the equalizing RBP's reliability and effectiveness has been proven through thousands of commercial applications.

Retrievable big-bore equipment
Also available commercially and proven effective through thousands of successful applications is the big-bore wireline retrievable packer, the workhorse of Halliburton's retrievable intervention solutions. The big-bore retrievable packer offers an enlarged diameter that enables a large number of intervention procedures in monobore tubing or casing strings, ranging from 2-3/8 inches to 9-5/8 inches internal diameter. Useful for suspending peripheral equipment in the well bore or for controlling or stimulating production, the big-bore retrievable packer can be used to guide water injection, isolate between production zones, or suspend a velocity string or sand screens. It also can be used to help deploy various well accessories, such as injection valves, standing valves, ambient-type safety valves, and gauges, orifices and chokes.

A modular retrievable straddle system incorporating big-bore packers is available to isolate production-string spans of more than 60 feet, using standard slickline or coiled tubing units. The desired straddle length is obtained by placing a big-bore retrievable packer in the string below the targeted zone, then consecutively stacking and anchoring a series of modular blank pipes on top until the zone is spanned, and completing the procedure with a big-bore retrievable packer atop the assembly.

The big-bore retrievable packer also can be deployed in tandem, with a length of blank pipe between an upper and a lower packer, to straddle and isolate damaged or leaky tubing. Or it can be deployed with screens for sand control or with a sliding sleeve to allow selective production from one or more geologic zones. The distance between the packing elements can be tailored to suit specific applications, and the big-bore straddle assembly can be deployed in one run to isolate as much as 60 feet of production tubulars and retrieved in two runs.

Retrievable intervention applications
The modular retrievable straddle system is recommended especially for applications in which there are height restrictions for the wireline lubricator. In one documented application, Kerr-McGee isolated 3,500 feet of 5-1/2-inch tubing in a production well converted to injector service after induced thermal stress caused many connections to leak. In the treatment program, Halliburton first set two mechanical barriers in the 5-1/2-inch string, using an electric line in two runs to insert and set a big-bore retrievable packer with an integral injection valve in the bottommost position and a big-bore retrievable packer with modular straddle system and a premium equalizing RPB below the target interval. With two mechanical barriers in the well, a 3-1/2-inch 3,500-foot string of coiled tubing hung by an upper big-bore retrievable packer was lowered into the well and anchored using the downhole power unit. Lastly, the equalizing RBP was retrieved and injection was resumed.

Another new retrievable, through-tubing intervention tool allows the introduction of gas-lift drive without need of a workover to a reservoir wellbore in which no gas-lift facility has previously existed, or enables injection of gas to a depth previously unavailable. In the procedure, a hole is punched in the tubing and the retrievable gas-lift straddle is set across it. Next a gas-lift mandrel equipped with a standard gas-lift valve is attached between the upper and lower packers, allowing metered gas injection from the annulus into the tubing. The gas-lift straddle is available to fit tubulars ranging in diameter from 2-3/8 inches to 9-5/8 inches, and it can be set across intervals of up to 60 feet in one run and retrieved during a second run across intervals of up to 60 feet via slickline, electric line, coiled tubing, or a workstring.

The downhole power unit is used to set the packer assembly of the new retrievable subsurface safety valve (SSSV) retrofit system. This system was developed for wells not equipped with a safety valve landing nipple or for situations in which the landing nipple is damaged and cannot be used to run a surface-controlled subsurface safety valve (SCSSV).

The so-called shallow set retrofit system can be installed in a live well and is slick line retrievable. It uses a surface controlled shallow set valve that is operated hydraulically through the newly created annulus extending from the installed packer to an adaptor spool at the surface wellhead. When hydraulic pressure is applied from the surface, the piston and flow tube are forced downward, opening the flapper. The hydraulic pressure must be sufficient to overcome the compression of the coiled spring and the force generated by the production pressure acting upon the area of the piston. Loss of applied annulus pressure allows the spring to close the valve thus shutting in the well.

With the wide range of affordable, flexible, retrievable intervention products and services available today, more reservoir problems and downhole mechanical failures than ever before can be solved without costly workovers or recompletions.

Simply put, if a well isn't performing as expected, there is more reason than ever to intervene in a timely manner and more low-cost, retrievable remedies available to assure the success of intervention, no matter where in the world a solution is needed.