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Advances in swellable elastomer packer systems are enhancing long-term well performance at reduced costs for operators by delivering greater flexibility in well design and more reliable isolation results.
Introduced to the market in the early 2000s, swellable elastomer packers are one-trip self-setting sealing products used to isolate annular spaces between tubulars and open hole or casing and address inflow control performance, including sand management. They are increasingly being deployed as an alternative to conventional cementing, mechanical, and openhole packer technologies.
Swellable packers traditionally have been used with single-fluid activation elastomers that expand in either hydrocarbon-based or water-based fluids. Oil-based elastomers, initially designed with a man-made EPDM polymer material that swells naturally in oil, operate in a diffusion-absorption process in which swell time and volume are determined by temperature and hydrocarbon composition. The swell rate is faster at higher temperatures and in lighter hydrocarbons as well as in lower-viscosity fluids.
A water-swellable elastomer is a nitrile-based rubber crosslinked with a super-absorbent polymer that facilitates swelling. The swell rate is faster at higher temperatures and lower salinities.
A flexible alternative
Among the breakthrough technologies that have emerged in recent years is the dual-fluid-activated swellable hybrid elastomer that can swell in hydrocarbons or water or a combination of both.
The fit-for-purpose method cross-links the super-absorbent polymer into the EPDM elastomer, providing a homogeneous blend of rubber that can swell at different rates depending on specific well conditions. Hybrid elastomers swell faster at higher temperatures and in lighter oils and lower salinities, and can swell up to three times their original volume in oil and/or water.
Weatherford’s hybrid elastomer technology is a swellable elastomer that is responsive to both oil and water in liquid, wet gas, or multiphase environments, providing reliable, long-term isolation. Hybrid elastomers eliminate the uncertainty of fluid type and also address the issue of absorption rates that vary depending on the type of fluid present and temperature.
Designed for use with a variety of packer systems, the hybrid elastomers allow swelling to occur in a controlled predictable fashion depending on well conditions. The hybrid elastomers also ensure long-term isolation because they continue to swell while making contact with wellbore fluids even after initial swelling.
The hybrid design is advantageous for numerous applications, including cases where an operator needs a packer to swell quickly or before a well begins production. Using the hybrid elastomer, the process can be expedited without occurring too quickly. The packer is initially placed in brine where it begins swelling at a relatively slow rate. When the well comes online with higher-temperature oil, the swelling process accelerates at a rate much faster than with a conventional oil-elastomer packer.
Another application is in oil wells where a water-producing zone develops. Deploying a hybrid elastomer provides a cost-effective alternative to running a long series of oil-based and water-based packers. The hybrid elastomer also addresses the temperature limitation of water-based elastomers, which are not recommended for use in environments that exceed 125°C (257°F).
A similar process is used for dry gas wells, where swelling occurs at a fast rate due to the low viscosity of the fluid and the higher temperatures. When a nonviscous fluid enters the matrix too quickly, explosive decompression can occur. To avoid that risk, packers equipped with hybrid elastomers are swelled in hydrocarbon fluid before the well comes online.
Since the hybrid elastomer was introduced in January 2009, it has been used with packer systems globally for a variety of isolation operations, including sand control.
In one case, a major operator encountered sand influx into a gravel pack that was interfering with production in a mature oil well producing water and sand offshore Azerbaijan. Swellable packers were selected as the most reliable isolation option, providing the operator with a five-week turnaround that could pass through flow-control profiles and seal in the screen without requiring a workover. The remedial technology was deployed through narrow 4½-in casing. The swellable packer also allowed the well to continue producing during the activation phase.
Because there was no clear evidence indicating whether the fluid concentration was water- or oil-based, there was uncertainty over which kind of elastomer to use. The Genesis Annulus Swellable Packer (ASP), suited for both openhole and cased-hole wells, was deployed with a hybrid elastomer, which was able to provide a seal regardless of fluid type.
The operation was executed within the desired time-frame. The sand was completely shut off within 30 days, with decreases in sand production evident within that period. The client plans to install the hybrid elastomer packers in more wells in the same field. Hybrid elastomers also can be used alongside water- or oil-based elastomers.
A major operator in West Africa required zonal isolation in conjunction with an expandable sand screen (ESS) sand control completion using swellable packers as the most cost-effective solution. The plan initially determined the use of water swellable elastomers because the completion fluid was brine, and isolation was required prior to the well coming online.
After brine samples were tested, it was determined that the swelling time would exceed the operator’s requirements. Further testing revealed the hybrid elastomer would provide similar results to water swellable elastomers in the brines. Because the packers would be in the reservoir section, they would be in contact with the in situ hydrocarbons, which would allow the oil swellable components of the elastomer to swell concurrently, achieving a faster swell to meet the customer’s requirements.
Through further well evaluation and discussion with the client, it was decided the sand control completion would use a combination of hybrid swellable and water swellable packers for the required zonal isolation. The completion was run successfully, and the well was brought online within the required timeframe. To date, production has exceeded expectations.
Pushing the technology
The hybrid elastomer also is used with the swellable Micro-Seal isolation system (MSIS), a low-pressure packer designed to prevent micro-annular fluid and pressure migration.
The seal provides micro-annulus conformity and sealing in spaces that form after cementing and against the outer diameter of the casing. Each MSIS seal is equipped with a slow-swelling H2W2 hybrid elastomer that does not respond to fluids in the well when the pipe is run or when the cement is curing.
The technology also has been incorporated into the ComboPac Open Packer system, a new concept that provides a combination of a conventional compression set element and a conforming swellable elastomer packer that can be used in both water and oil swellable versions. The system is designed for a broad range of nonuniform, openhole environments and has a lower pressure rating and smaller outer diameter that can be installed in a variety of hole deviations. The system is effective for open-hole completions and isolating sand screen sections and in long horizontal wells.
Since it was introduced nearly three years ago, the hybrid elastomer has been deployed on more than 200 conventional packer systems and 400 MSIS systems worldwide. It is applicable for all well and reservoir conditions, and its use is expected to be expanded to additional markets with today’s increasingly complex wells.