Remedial annular cementing

THE PROBLEM
A study was performed on the South Arne field investigating the causes and implications of instances of conductor slippage. The study report recommended remedial cementing on 2 wells (SA-3 & SA-5) to ‘provide the best chance for saving the well in the future’. The cement tops in the selected wells within the 30” x 13 3/8” annulus were below the 30” shoe.

Therefore, the objectives of the remedial cementing operations were to:

1. Squeeze cement into the void spaces and formation around the 30” shoe to improve integrity.

2. Fill the 30” x 13 3/8” annulus of the wells with cement to prevent overload damage to the 13 3/8” casing in the event of the 30” casing losing support to the point of slippage.

To achieve these objectives it was essential to be able to pump cement down the 30” x 13 3/8” annulus on each well. However, the well construction did not allow for any easy method of achieving these objectives since the annulus was open to the sea at the mud line.

This meant that the cement was not be able to be pumped down the annulus without first sealing it at the sea bed, as the tendency would be for the cement to return up the open annulus, rather than being pumped to the desired location.

THE SOLUTION
The key piece of equipment to allow remedial cementing operations to take place was a Claxton designed Annular Sealing Unit (ASU), which allowed the annulus to be pressurised and prevented the upward cement flow. In addition to a seal at the seabed, the annulus is also sealed at the surface, between the 20" tieback string and the 13 3/8” string. With the annuli sealed cement is injected through the ASU subsea.

THE RESULT
Operations on SA-3 allowed 27 bbls of cement to be pumped. This completely filled the annulus.

On SA-5 100bbls of cement slurry were pumped and displaced with 100bbls of sea water ensuring a good cement bond around the shoe of the conductor. The cement job was deemed a success and further cementing operations on SA-5 not necessary. Cementing of wells SA-1, 2 and 4 was carried out in one run. Each of them was topped up with 7-9bbls of cement.

The project was completed to schedule and with no incidents or lost time. Claxton also supplies cement top up services for drilling operations - see the Claxton cement top-up system, here.