Arie Vliegenthart - Swellfix
Cement has been used in the completion of wells in the oil and gas industry for decades. It is the established technology trusted by operators and service companies alike, but it has its drawbacks.
Cementing is time-consuming, costly, and requires specialist personnel and equipment. Cement can also crack and produce micro annuli during the life cycle of a well, due to temperature and pressure fluctuations. Until recently, however, a proven alternative has not been readily available, so cementing has remained the first-choice method of well completion.
Swellfix was born out of Shell’s well technology R&D program. The company made its first swellable packer in 2002 for an application for PDO in Oman, and has since deployed more than 4,500 of these units in wells around the world.
Swellfix testing procedure.
Downhole swellable elastomer technology is essentially very simple. A swellable compound is applied on the outside of the casing: when the compound comes into contact with the fluid it is designed to react with – oil or water – it swells to fill the annulus and to create a high pressure seal.
The science comes in matching the compound to the well fluid. No two wells have the same mix of fluids, with variations in both the composition of the oil, and the salinity and chemicals present in the water. In response, Swellfix has developed more than 2,500 swellable elastomer compounds so that each application can be matched to the conditions of the well.
The company’s zonal isolation products come in two basic types, oil swelling (solvent swelling), and water swelling (osmotic swelling). The latter has had the most noticeable impact. Operators essentially want to produce more oil and prevent water ingress, so it is logical to have a zonal isolation product that specifically targets the water. An osmotic swelling elastomer packer basically uses water to stop water.
Cement failure back-up
Wells often suffer from the formation of micro annuli caused by damage to cement from pressure and temperature changes as well as minor geological movements.
The failure of cement usually occurs between the cement and the casing, rather than between the cement and the formation. This is due to the temperature and pressure variation resulting in a cyclical expansion and contraction of the casing, to which traditional cement cannot respond, leading to a small flow of gas or fluid that can get worse over time.
Swellfix C-ZIP (Cement Zonal Isolation Profiler) swellable elastomer products are being used by many operators around the world to protect against the effects of cement failure. The C-ZIP features a thin layer of swelling rubber bonded onto the casing. The elastomer is manufactured under controlled conditions to react and swell when it encounters well fluids following a breakthrough from a micro annulus. The product performs reliably and consistently and, with no moving parts or specialist running tools required, is simple to install: C-ZIPs are deployed like any other piece of casing pipe.
Once at depth, the elastomer packer simply waits. Should the well’s cement fail at any time, there is a remedial solution already in place. If a micro annulus forms, fluid movement, water or oil, activates the dormant rubber element causing it to swell to fill the space vacated by the retreating casing. The elastomer is designed to swell sufficiently to bridge the gap between the casing and cement.
If there is a risk that cement may disappear into a thief zone, therefore not going up the well as intended during the casing process, the swellable elastomer solution can be designed to fill the entire gap between the casing and the formation. In addition to providing a good seal, Swellfix’s research has demonstrated that the elastomers also provide structural integrity to the casing due to a combination of vulcanization to the pipe and “mating” with the formation – the process in which the rubber grows into the porosity of the formation.
As a C-ZIP swells to the reach the remaining cement it “grows” into the cement profile, creating a permanent seal and restoring well integrity. The elastomers retain a great deal of structural rigidity by controlling the expansion ratio, allowing the unused swell to exert a force between the casing to which the elastomer is bonded and the cement or formation, the result being an extremely long-lasting packer element.
The C-ZIP repairs damaged cement without requiring intervention or incurring additional costs. Crews may even be unaware that a well below their feet has just healed itself.
Horizontal well demands
As the ability to drill very long horizontal sections has improved, the demands placed on cement have increased. In some cases cement simply isn’t an option due to physical space restriction and such wells have been often completed “barefoot,” without any provision for zonal isolation. This can be a risk, however, if there are any concerns about water breakthrough or formation damage.
Swellable elastomer packers offer a solution that can deliver the simplicity and speed of open hole completions with the zonal isolation and case fixing benefits usually associated with cement.
Swellfix expandables in a horizontal side track.
When a major North Sea operator decided to side track a 20-year-old well in an offshore field, it identified potentially significant savings by opting for through tubing rotary drilling (TTRD). However, with a 2 7/8-in. (7.3-cm) completion in a 3 3/4-in. (9.52-cm) hole, the wellbore would not be large enough to allow for cementing.
Based on extensive knowledge of the mature reservoir, the operator knew a contingency would be needed for water management. The optimum solution would enable use of TTRD while still providing effective zonal isolation.
The operator decided to deploy Swellfix’s E-ZIP (External Zonal Isolation Packer) swellable packer system both to fix the casing and to provide protection against water breakthrough. The E-ZIPs deployed in the horizontal sections of the well feature a combination of oil and water swellable elastomers vulcanized directly on to 2 7/8-in. pipe.
E-ZIP sections were deployed in an oil-based mud (OBM). When the oil swellable sections came into contact with the mud, they swelled to fill the narrow space between the pipe and the hole to deliver an effective seal.
Swellfix expandable elastomer packers.
The water swellable elements in the E-ZIP system are designed to remain dormant in the well until they encounter water, at which point they will swell and provide additional sealing capacity. This design means that the well is pre-prepared if water intrusion becomes an issue at some point.
The operator ran eight packers in the horizontal section of the side track at depths of 13,500-15,300 ft (4,115-4,663 m), each with 16 swellable elastomer elements. This configuration was designed to give the greatest pressure holding ability, a fast setting time, and flexibility, making it easier to deploy multiple packers in the long-reach horizontal sections. At the oil-producing zones between the packers the operator introduced pre-perforated pipe, leaving blank pipe where water-producing zones were suspected.
Valhall test
Swellable elastomer packer technology may be relatively new but Swellfix already has deployed more than 4,500 swellable elastomer packers downhole without a single failure. This level of reliability is something that can never be guaranteed by cement, due to the complexity of its application and the number of variables involved.
Recently, BP Norge successfully tested Swellfix’s swellable elastomers to pressures of more than 9,000 psi and cycled the packers through temperatures ranging from 16º C to 90º C (61º F to 194º F).
This simulation of extreme downhole conditions was used to prove the technology before its application in the operator’s Valhall field in the Norwegian North Sea. The findings of the test program, which included proving the swellable elastomers beyond their design specifications, support experience in the field.
The range of applications for swellable elastomer packers continues to grow as new products are developed and operators present the technology with further challenges. It has now been demonstrated that swellables can be employed as a back-up to cement and as a practical alternative to cement in many horizontal wells.
Cement is going to be increasingly challenged and we believe eventually replaced in many applications by swelling elastomers, particularly in horizontal reservoir sections where operators are seeking the benefits of this technology to segment the reservoir into small manageable sections. We are running our swellable elastomer packers as back up to cement jobs and it will not be long before someone decides to let the back-up solution become the primary one.
The reality is that there are very few well completion situations where swellable elastomers could not be applied in place of cement. So a future without the complexity and risks associated with cement is a real possibility.
By combining the downhole expertise of companies such as Schlumberger, Weatherford, and BJ Services with our technology, we are confident that the application of swellables will eventually become the trusted and accepted norm for most completions.
