A major concern in drilling operations is the problem of carrying out cementing jobs for production casings where no fracture margin during the slurry displacement exists. In general in order to resolve this problem, a double stage cement job, the use of a liner with a subsequent tie-back or one more casing string is required.

In the Adriatic Offshore we have experimented with the use of light weight high mechanical resistance slurry (SG = 1.6 / 1.7 kg/1) in 7" production casing cement jobs in order to complete the operation in a single stage.

These cement jobs have been carried out, with positive results, in six of the fourteen Angela platform wells, in three of the four Antonella platform wells, in one Anemone cluster well (double stage cementing to avoid one more casing string), in the Antares 1 s.t. and the Agostino 11 s.t. wells.

The wells, where the 1.6 / 1.7 Kg/1 light weight slurry has been used, have an average total depth of 3600 m VD, their intermediate casing shoes are set at an average depth of 1800m VD.

The use of light weight slurry, composed of 10 / 30 % Microsilica by cement, has led to a reduction in the hydrostatic load, an optimisation of rheology and filtration control (maximum differential pressure of 400 atm exist at the end of displacement) while guaranteeing the necessary high mechanical resistance.

According to field data, we can conclude that the use of light weight slurry has the following advantages:

  • a single stage cement job can be used instead of the more complex double stage one with the consequent improvement in well and rig safety; in particular cases, a light weight slurry can avoid setting one more casing string;

  • improved quality of the cement job in comparison with the not always reliable results of a double stage cementing;

  • operational time and cost reduction.

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