Tendeka has the in-house capability to custom design a range of sealing solutions, from non-standard diameters to unique fluid parameters, ensuring the end result is a perfect fit for well projects. SwellStack is designed to seal inside damaged and corroded seal bores within downhole safety valves, restoring production and maintaining well integrity.

The ChallengeDue to intervention techniques, downhole safety valves can become corroded or damaged due to wireline activity. Standard chevron stacks commonly provided with safety valves are unable to seal in this damage and prevent any leak that can lead to hydrocarbons migrating up the control line. Prior to Tendeka’s development of the SwellStack, a patented technology, the only option of a leaking safety valve was to perform a straddle or workover, and replace the damaged valve. This proved to be costly and time consuming.

Tendeka’s sealing solutionIn 2013, Tendeka developed and released SwellStack, a swellable sealing solution which can be installed on an insert safety valve in place of an existing chevron stack, to seal in any damage in the bore and successfully withstand the required pressure of the existing DHSV.

Originally designed for a major North Sea operator whose leaking safety valve resulted in the well being shut in, the SwellStack solution has since been used with multiple operators globally to regain the integrity of downhole safety valves. Comprising of a swellable seal element, and multiple chevron seals, the swellable element seals any damage in the seal bore and activates the chevron seals, effectively providing a seal.

Easy to install with no further intervention required, the SwellStack can be used in damaged bores of up to 0.063”, maintaining a continuous working pressure of 5000psi to successfully regain well production.

North Sea, UK

Tunisia

Nigeria

Denmark

Gabon

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20Tendeka has successfully installed 163 SwellStack Sealing Systems globally.

SwellStack overview

Example of SwellStack Configuration

1. Swellable Element - Oil or Water Swell2. Inner V-Seal3. Centre V-Seal4. Stainless Steel End RingDue to valve size, further chevron seals may be added.

SwellStack pressure testingTendeka has performed numerous tests on the SwellStack sealing system in order to determine performance limits, and to successfully qualify for oil and water swell compound use. The SwellStack has been qualified to 5000psi continuous working in pressure in 0.063” wireline damage.

A summary of the testing is below.Oil SwellStack sealing in 4.562” with 0.060” groove - Clairsol NS,80OC

Water SwellStack sealing in 3.812” with 0.029” groove - Glycol, 21OC

Water SwellStack sealing in 4.562” with 0.063” groove - Glycol, 40OC

The full test results can be seen on the following page.

SwellStack swell times are dependent on temperature of the fluid which will be exposed to the SwellStack, and the fluid composition. The higher the temperature the faster the swell.

SwellStackDownhole safety valve swellable sealing systems

SwellStack pressure testing results

Full Scale SwellStack Testing

3.812” Water Swell (0.029” groove)The test was set up in accordance with test procedure TP-597

Details of SwellStackThe test fixture was set up with a water SwellStack designed to seal in 3.812” safety valve. The seal bore of the fixture had a 0.029” groove machined to simulate the coil tubing wear inside the valve (figure 1).

The fixture was then filled with Oceanic HW540E and the temperature increased to 21°C the fixture was left to swell until day 4 where the element contacted. On day 4, the temperature was increased to 30°C and pressure testing commenced. On day 4, a 3-hour 7000psi qualification hold was obtained and held overnight. On day 5, the pressure was reversed and a further 3-hour 7000psi hold was obtained in the opposite direction (figure 2).

Details of SwellStack Push Out TestThe SwellStack was pushed out of the assembly, following TP-597. It required 108psi to push out of the fixture, figure 4. The 108psi was acting on an area inside the fixture of 11.413in² which equates to a retrieval force of 1232lbs. As seen in figure 3, the retrieved element and back up ring system are in good condition with minimal extrusion at the grooved position in the seal.

ConclusionTendeka successfully qualified the water SwellStack for 3.812” valve size, with successful 7000psi pressure holds in 0.029” damage. The SwellStack required 1232lb of force to be retrieved.

Figure 1: Seal bore groove

Figure 2: SwellStack pressure test chart

Figure 3: SwellStack after push out

Figure 4: SwellStack retrieval test

A to B

B to A

Push Out Pressure

Time (hours)

Time (hours)

Pres

sure

(psi)

Pres

sure

(psi)

Tendeka have tested the amount of force required to retrieve a SwellStack and received feedback from customer’s retrieving in the field.

Retrieval force is dependent on:

• SwellStack size

• Rubber compound (e.g. oil / water)

• Damage in bore

• Number of SwellStacks (e.g an upper/lower valve stack)

Field Testing

Test 1

A customer performed a retrieval test on an oil 3.813” SwellStack, which had successfully held for a 6500psi test. The customer required approx. 2200lbs to retrieve.

Test 2

A customer was required to retrieve a safety valve with a 4.562” and 4.625” swollen upper and lower water SwellStack. They successfully retrieved the valve on 7/32” wire, and required 50 jars.

Test 3

A customer retrieved a 4.562” oil SwellStack using 0.140” wire, which required roughly around 3200Ibs–3400Ibs

Workshop Testing

Test 1

As detailed in SwellStack Test 2, the 3.812” water SwellStack required 108psi to push out of the fixture (figure 5). The 108psi was acting on an area inside the fixture of 11.413in² which equates to a retrieval force of 1232lbs.

Test 2

A further test was conducted using a strain gauge on a 4.562” SwellStack which required 3058lbs to retrieve (figure 6).

Retrieval of SwellStack system

Figure 5: 3.813 Retrieval

Figure 6: 4.562 Retrieval

For further information click here to see the SwellStack datasheet.

SwellStack Track Record

Year Country Qty Well Fluid Valve size BHT (degC)

Pressure PSI

2017 UK 8 - 2016 UK 8 Water based control line fluid 3.750 44 75002016 UK 2 Water based control line fluid 4.562 65 50002016 Tunisia 2 Mineral Oil 3.812 180 50002016 UK 2 Oil based control line fluid 3.812 130 50002016 UK 4 Water based control line fluid 2.812 83 42002016 UK 4 Oil based control line fluid 3.813 72 70002016 UK 2 Oil based control line fluid 3.813 - 50002016 UK 2 Oil based control line fluid 4.562 125 58002016 UK 4 Oil based control line fluid 5.963 45 35102016 UK 2 Water based control line fluid 4.625 40 42002016 UK 2 Water based control line fluid 4.562 40 42002015 UK 3 Water based control line fluid 6.395 5 -2015 UK 3 Water based control line fluid 6.229 - -2015 UK 2 Oil based control line fluid 3.813 - 50002015 UK 3 Water based control line fluid 6.229 - -2015 UK 3 Water based control line fluid 6.229 - -2014 UK 4 Water based control line fluid 4.562 70 50002014 Nigeria 20 Oil based control line fluid 4.562 78 50002014 UK 1 Water based control line fluid 3.81 78 65002013 UK 4 Oil based control line fluid 5.000 90 60002013 UK 1 Oil based control line fluid 5.000 50 60002013 UK 3 Oil based control line fluid - - 60002013 Denmark 2 Oil based control line fluid 3.812 80 60002013 UK 3 Oil based control line fluid 5.000 100 60002012 UK 3 Oil based control line fluid 4.578 100 60002012 - 2 Water based control line fluid 3.750 10 50002012 - 2 Water based control line fluid 3.812 10 50002012 - 2 Water based control line fluid 3.812 10 50002012 UK 4 Oil based control line fluid 4.562 110 50002012 UK 25 Oil based control line fluid 4.562 100 60002011 Gabon 25 Oil based control line fluid 4.562 110 50002010 Gabon 4 Oil based control line fluid 3.812 110 50002010 UK 2 OBM 3.813 110 5000

Case Studies:SwellStack regains well integrity without requirement for workover

BackgroundClient had a damaged SCSSSV, existing isolation system was damaged and could not stop the leak through the valve. A more robust sealing solution was required to ensure long-term production of the well. The challenge was to design a seal system strong enough to hold 5000psi differential pressure in a damaged seal bore with possible corrosion. The system also had to be flexible in order to be retrieved from the safety valve when required.

Damaged chevron stack Replacement SwellStack system

SwellStack extends life of surface control sub-surface safety valve

SwellStack showing deformation

and put back on production. The well was flowed briefly to increase the surrounding temperature at setting depth, increasing swell performance and reducing time before the valve held pressure. By installing the SwellStack system, it extended the life of the safety valve and avoided the alternative of an expensive workover that would have involved pulling the completion to replace the entire system.

Project ResultsWithin 24 hours, the SwellStack was installed, activated and was holding the required pressure of 350 bar / 5000psi. By installing the SwellStack system, it extended the life of the safety valve and avoided the alternative of an expensive workover that would have involved pulling the completion to replace the entire system. Well integrity was regained and was placed back on production without the requirement for a workover.

BackgroundThe challenge was then to design a seal system strong enough to hold 5000psi differential pressure to deal with an estimated 0.060” deep wireline cut in the seal bores and possible corrosion. The system also had to be flexible in order to be retrieved from the safety valve when required.

Project Results

The resulting SwellStack packer opposite clearly shows deformation in the seal where the compound had adapted to the damaged seal bore profile. Well integrity was regained

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