Versatile Swellable Packer Tool Provides Reliable and Economical Zonal Isolation

Abstract

Technology Update A simple observation of the expansion of a child's toy snake in water by a lateral-thinking Shell R&D technologist a few years ago has led to an emerging revolution in the oil and gas industry—swellable-elastomer packers. Following rapid industry acceptance, the technology now can be found downhole in wells in every producing region of the world, and the technology recently won a major international award for applied innovation. Versatile, Highly Reliable Technology The underlying objective of using swellable-elastomer packers, most of the time, is to reduce water production and increase oil and gas production proportionally. Swellable packers combine the advantages of mechanical and inflatable packers, without the inherent complications associated with the traditional technologies. Swellable packers adhere to the profile of the formation in a reliable and efficient manner, and like conventional packers, they create a pressure-holding seal within the wellbore. However, unlike traditional methods of zonal isolation, swellable packers always have something in reserve in the event of a future washout or water break-through. In such cases, the packer will swell further and adapt to the new structure until a seal is re-established (Fig. 1). The packers themselves are thin sections of swellable rubber that are vulcanized directly on to standard tubing. The rubber swells when it comes into contact with the appropriate fluid, water or oil. The basic principle is natural and very simple. Add water or oil to an appropriate rubber-based compound, and it will swell as it absorbs the liquid. There are no moving parts to fail, and as long as the application is correctly engineered and deployed, there is very little that can go wrong. However, the key factor is engineering it properly in the first place. The simplicity of swellables belies the science and vast body of research behind the technology. Literally thousands of tests have been conducted on a multitude of compounds, under different oilfield conditions, to make sure that the swellable elastomers will perform exactly as they should downhole. Swellable packers are not a one-type-fits-all technology. Elastomer compounds numbering in the hundreds are needed to meet a vast range of downhole requirements. An exhaustive testing program by Swellfix has found that various characteristics of particular crudes, different oil/water mixtures, and other specific well factors all affect how various swellable compounds perform. A comprehensive understanding of the relationship between packer composition, well fluids, and swelling enables selection of the appropriate compounds for best performance. In 5,000 swellable-packer deployments by Swellfix, no failures have yet resulted. Water- and Oil-Swellable Packers Water-swellable elastomers work on the principle of osmosis, a process that encourages the movement of water particles across a semipermeable membrane, where there is a salinity difference on either side of the membrane. Effectively, the water is drawn into the elastomer and retained because of the salinity gradient across the surface of the elastomer. This causes it to swell, increasing its size to fill a void.