Turning water into oil
Swellable elastomers, the simple and reliable method of preventing water breakthrough
When Shell and PDO faced production problems and delays on more than 2,000 wells in Oman, it presented the operator with a challenge. After researching and reviewing its options, the company identified that recently developed swelllable elastomers could reduce the water cut and increase production.
The concept of downhole swellable elastomer technology has moved decisively from the lab into the zonal isolation market over the past few years and is increasingly being utilised as solutions for wells – Swellfix has installed more than 3,000 swellable elastomers down hole, across virtually every oil producing region in the world.
Swellable technology
The basic principle of swellable elastomers is natural and very simple. Add water or oil to the appropriate rubber based compound and it will swell as it absorbs the liquid. There are no moving parts to fail, so as long as the specific application is correctly engineered and deployed, there is very little that can actually go wrong.
However, the inherent simplicity of swellable materials masks the real skill required in a created swellable packer solution for a well.
Although there are essentially only two main types of swellable elastomers used for down hole packers – oil or water swelling – thousands of different compounds have been researched and developed so that the swelling characteristics can be matched to the specific well conditions.
Water swelling elastomers work on the principle of osmosis, a process that encourages the movement of water particles across a semi-permeable membrane, where there is a salinity difference on either side of the membrane.
Oil swellable elastomers work on the principle of absorption and dissolution. The swelling rate and volume increases are directly related to the composition and characteristics of the oil. The specific gravity of the oil plays an important role, but other qualities of the oil can also affect swelling behaviour.
Traditional Methods
One method traditionally used in zonal isolation is cementation. When oil well cement is used for zonal and inflow control, this can have a number of disadvantages as cement shrinks on setting, is brittle after hardening and its unpredictable setting time can put tools or even the well at risk.
Like cement, swellable packers adhere to the profile of the formation, and like conventional packers they create a pressure holding seal within the well bore. However, unlike these traditional zonal isolation methods swellable packers always have something in reserve in case of a washout in the future, or if water break through occurs. In such cases the packer will swell further and adapt to the new structure until a seal is re-established.
Metal expandables can also be sufficient in a number of situations but offer limitations as wellbores are not as always round, and a product that could expand in water or in oil has provided a new sealing tool for engineers.
Deployment of elastomers
Deployment of elastomers in high water cut wells can improve production and one case where the deployment of elastomers in high water cut wells significantly improved production was in one well operated by PDO in southern Oman. The well was producing just 107 net barrels of oil per day with a 90% water cut, prior to the installation of swelling elastomer packers. After the technology had been deployed, maximum oil production from the well climbed to more than 1,258 barrels of oil per day and water cut was reduced to just 22%. The design life for the solution for the well is typically 20 years or more.
PDO and Shell have been deploying expandable elastomers in Oman since 2001. By 2003 they were comfortably installing what is now the X-Zip (Expandable Zonal Inflow Profiler) product. Mounted on an expandable pipe, the X-Zip is very simple in operation and is expanded downhole with the pipe to the nominal hole size. The X-Zip’s elastomer provides the extra capacity to create a compliant seal in sections where the hole is not in gauge. Having installed more than 50 X-Zips, PDO and Shell then embarked on a programme of installing E-Zip packers (External Zonal Isolation Profiler) – swellable elastomers fitted around a tubing or liner in an open hole to shut off water outside the production tubing – across faults in the formation in the Nimr field. 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 now pre-prepared if water intrusion becomes an issue at some point in the future.
With a detailed understanding of exactly how any of the myriad of swellable elastomer compounds developed will react in the conditions it encounters, the company can accurately predict safe run in time, the time to first swell and the amount of unused swell available to hold pressure. The first eleven wells tested with E-Zips in the Nimr field averaged two to three times more oil production after installation.
In the case of PDO’s use of X-Zip, each deployment consists of elastomers for between eight and ten joints in each well and this is now standard completion for PDO in Oman.
PDO now has a flexible low risk, low cost solution to prevent water ingress that can be used in both existing and new wells.
The success of the initial deployments in southern Oman, resulted in PDO testing swellable elastomers as a back up for zonal isolation in its Yibal field in the North of the country, where a record has since been set for the longest open hole clad and open hole liner installation with a swellable elastomers at 1,000 metres.
