Reliability, simplicity and operating time are key considerations in designing any drilling and completion program in the oil and gas industry. This is especially true in offshore operations because of the considerably higher daily rig rates and operating costs. But it is also true on land and at remote locations where improved efficiencies are also desired.
Acquiring pressure and flow isolation points in a well, either along the casing and/or completion strings, is a continuing requirement. Increasingly, well environments have become more complex due to operating environments with deeper, hotter, and higher pressures that require more complicated completion designs. However, the requirement for effective, long-term isolation points has remained the same.
With the added challenges that must be addressed in today’s wells, traditional methods of achieving the required isolation have become more problematic, and often have further increased the complexity of the wells. Simultaneously, oilfield trends exhibit an increased need for simplified operations that enhance reliability rather than make it more complex.
Recently, an innovative technology that utilizes swellable rubber packers to simplify the achievement of isolation requirements was introduced to the oil and gas industry. The technology is based on the swelling properties of rubber elastomers in the presence of either liquid hydrocarbons, or water which causes the elastomer to swell and effectively seal the annulus around the pipe. Since 2001, these packers have proven to be a robust, reliable, and cost-effective solution for achieving long-term isolation in a simple, safe and extremely reliable manner.
Since their introduction, swellable packers have undergone a great deal of additional development involving the basic swellable elastomer technology, both hydrocarbon and water swelling, as well as the temperature and pressure ranges in which they can be employed.
Halliburton’s Delta StimSM completion service showing Halliburton’s Swellpacker systems isolating various zones of a horizontal wellbore. All zones are stimulated using an intervention-less frac. In this un-cemented, openhole example, the ball-drop method is used to operate the completion system
In swellable packers, either oil- or water-swelling elastomers are bonded onto a basepipe, alternatively ‘slip on’ tools can be utilized, held in place with stop collars. The size, metallurgy and thread of the packer are the same as that of the rest of the casing or completion string (any size) being used. These packers are run as part of the completion or casing string and are spaced on the string according to the depth at which the isolation point is required. When the packers come in contact with a hydrocarbon or water, they swell (to a maximum of 200% by volume) and seal off the annulus. Depending on the dimensions of the packer, and the percentage of swell, differential pressures of up to 10,000 psi can be achieved by these tools.
There are a number of benefits associated with this technology. First, the setting of the packers requires no pumping, rotation, running/setting tools, pressure, dropping balls, additional trips etc. This simplifies the overall operation because there is almost never a need for a dedicated operator to be present during the running of the packers.
Second, since the packers are mounted onto basepipe having the same characteristics and specifications as the rest of the string, there is neither an ID reduction nor potential weak spot or leak path through the tubing, which is often the case with traditional inflatable isolation tools. As the rubber swells, it is able to mold itself and seal the annulus in open or cased hole environments.
Finally, in the event that temperature or pressure changes should occur and a leak path form during the life of the well, the packer would simply be activated to swell into the flow path and seal off the leak as long as the fluid in the path is a type that originally caused the packer to swell (hydrocarbon or water). Contrastingly, if traditional methods have been used to achieve isolation, either through standard inflatable packers, or cement, and a leak path or micro-annulus forms, it becomes very difficult and costly to resolve.
Although the technology is relatively new, it has been widely accepted and utilized by the industry. To date, it is estimated that approximately 9,000 swelling products have been run for over a 126 different clients in 46 countries.
Globally, there exists a wide variety of well challenges that will benefit from applications of swellable packer technology. These applications include:
• Water or gas shut-off, along screens or perforated liner. Traditionally, achieving isolation of unwanted zones along an interval completed with screens or pre-perforated pipe, or along sections where typical isolation methods are unsuccessful (low pore/frac pressure, slim hole, for example) has been very difficult. This often leads to premature water breakthrough, unacceptably high water or gas cut, and possibly even loss of recoverable reserves.
The lack of annular isolation also leads to difficulties involving how to perform a workover on the well, as either shutting off, or stimulating a zone (as there was no annular isolation to control treatment fluid flow). Running swellable packers along the screens, liner or casing, located at zone interfaces, enables unwanted zones to be reliably isolated behind solid pipe. This is particularly beneficial in situations where low formation fracture gradients can cause difficulties in achieving the required isolation with traditional cement jobs, or where long horizontal sections traditionally have proven difficult to isolate. Clients have reported total well construction cost savings of over 30% by utilizing swellable packer technology in this application.
• In combination with traditional cementing operations. Oil and gas wells throughout the world suffer from sustained annulus casing pressure at surface, or from underground cross-flow between zones. This can lead to contamination of zones, loss of production, or excessive water or gas cut. The use of a Cement Assurance™ tool can help avoid these issues.
The Cement Assurance tool uses swellable packer technology to help assure that isolation is achieved at the required depth. This assurance is provided by the use of a thin layer of swellable elastomer mounted on the casing (either bonded, or slipped on and held in place with stop collars).
The Cement Assurance tool is run with the casing. If a mud channel or a micro-annulus forms while the cement is curing, or at some stage through the life of the well, cement isolation failure may occur. Should either of these events occur, the Cement Assurance tool will come in contact with the fluid traveling in leak path past the tool and cause it to swell and seal off the leak
• In combination with Delta Stim® sleeves on multi-stage well fracturing. In this application, technologies are combined to enable an operator to initially achieve reliable isolation using a swellable packer. Then, in quick succession, the operator can execute a multiple-stage frac job by opening the Delta Stim sleeves that have been placed across the various frac zones. This application can reduce the well’s total fracturing time, as well as avoid perforating and cementing requirements. Later, the sleeves can be utilized throughout the life of the well to close off unwanted zones, as required.
• Excessive plugging from shale or solids movement along the annulus of a screen section. Shale or solids movement along the annulus of a screen section can cause excessive plugging which can result in reduced production, hot spots, and possible loss of sand control. Swellable elastomers mounted on a sleeve that has been placed over the pin end of screens will swell and stop any movement of fines across the packer. This will help retain the well production and avoid costly screen plugging and subsequent potential “hot spots.”
In summary, the use of Halliburton’s Swell Technology™ systems can offer operators operational cost savings and improved return on their investment by enhancing production performance in a simple, reliable and robust manner. Numerous applications exist for the use of this technology which is available worldwide.
By Henry Longden, Halliburton