How Does a Swellable Packer Work?

Wed, 01/25/2012 - 11:29

In order to isolate a zone in a well, cementing and perforating are the tools traditionally employed. However, in certain situations cementing can adversely aect the well’s productivity. For example, cementing a horizontal well with thin oil sand can serve to cover up most of the sand face. It can also cause problems for some unconventional reservoirs that require fracturing techniques, as the cement job can force fracture treatments to be pumped through perforations.

Swellable packers provide an interesting alternative to this method. A specially designed elastomer is used that absorbs oil through diusion, and this attached to API pipe with weight, grade and connection specified by the well design. Once the packers are inserted into the well, the elastomer from which they are fabricated expands. Whilst originally this would only happen on contact with oil, packers have now been designed that will swell when they meet water, or a combination of both water and oil. The packer expands up to three times its run-in volume, until the point where it makes contact with the inside of the open hole, sealing the well casing. The swelling continues until the point where the stresses inside the elastomer reach the level where swelling can no longer occur. Swellable packers can be pressurized to 10,000 psi. The exact size of the seal is determined by dierential pressure, the well temperature, and application. For low-pressure wells, a slip-on version of a swellable packer is available, which are often used to provide annular isolation for slotted liners and flow barriers.

This technology has a number of applications, from zonal isolation to flow diversion, stimulation, intelligent wells, selective production, cement enhancement, gravel packing, fracturing, and water or gas shuto. One of the biggest advantages of swellable packers are their simplicity to install. One particular use in Mexico is for wells where Pemex is using steam injection, as some models of swellable packer can be applied in temperatures up to 315°C. Pemex is increasingly using steam injection in its southern onshore projects, particularly at the Samaria field. Swellable packers can be inserted into horizontal wells on such projects, and expanded in order to isolate particular parts of the well to steam injection.

Swellable packers can also be used to maintain a well’s cement integrity. Failure of a well’s cement sheath can lead to declining production, sustained pressure on the well casing, and early water production in a well. Cement jobs come under pressure in most wells as a result of drilling activity, changes in well pressure and temperature fluctuations. A normal approach is to bring in a workover rig to re-cement a well, but a swellable packer can also be used as an alternative. Because the packers react to well-bore fluids, drilling mud and completion fluids, when inserted into a well where a micro annulus or mud channel has been created in the cement casing due to well stress, the packer will expand to fill the flow path of the liquid, thus supporting the cement and stopping the flow of any undesirable fluids between the cement job and the well