Remedial conductor annulus cementing, South Arne field
Annular cementing challenges – overcome by Claxton project engineering team.
A study on the South Arne field in the Danish North Sea investigated the causes and implications of conductor slippage in the field. The report recommended remedial cementing on two wells (SA-3 and SA-5) to “provide the best chance for saving the well in the future”. The cement tops in the selected wells within the 30- × 1133/8-in.annulus were below the 30-in shoe.
Consequently, remedial cementing operations would aim to
- squeeze cement into the void spaces and the formation around the 30-in. shoe to improve integrity
- fill the 30- × 133/8-in. annulus of the wells with cement to prevent overload damage to the 133/8-in. casing in the event of the 30-in. casing losing support to the point of slippage.
To achieve these objectives, it was essential to be able to pump cement down the 30- × 133/8-in. annulus on each well. However, the well construction did not offer an easy method of achieving these objectives, as the annulus was open to the sea at the mudline. This meant that the cement could not be pumped down the annulus without first sealing it at the seabed, as the cement would tend to return up the open annulus, rather than going to the desired location.
The key piece of equipment for the remedial cementing operations to take place was a Claxton-designed annular sealing unit, which enabled the annulus to be pressurised and prevented the upward cement flow.
In addition to having a seal at the seabed, the annulus was also sealed at the surface between the 20-in. tieback string and the 133/8-in. string. With the annulus sealed, cement could be injected through the annular sealing unit subsea.
For well SA-3, 27 bbl of cement was pumped, which completely filled the annulus. For Well SA-5, 100 bbl of cement slurry was pumped and displaced with 100 bbl of sea water to ensure a good cement bond around the shoe of the conductor.
The cement job was deemed a success and further cementing operations on SA-5 were unnecessary. Cementing of wells SA-1, SA-2 and SA-4 was carried out in one run. Each was topped up with 7–9 bbl of cement.
All aspects of the project were carried out highly satisfactorily. The cement top-up project had excellent health, safety and environmental performance and was completed on schedule without any accidents or incidents.
Claxton has a world-class in-house design and project engineering team that enables its clients to access technically robust solutions for challenging issues and be sure of success.