Brazil deepwater reservoirs in the presalt area of Santos basin are typically thick hydrocarbon- and water-saturated limestones. Long-term zonal isolation is required to correctly exploit the reserves, to effectively perform stimulation operations and to control water and / or unwanted gas production.
For the case presented, CO2 is expected to be produced commingled with the hydrocarbon production. Also, salt formations are present at the top of the production zone. Thus, the cement needs to include both CO2 corrosion control and salt control in order to provide long-term zonal isolation, as well as to protect the well?s casing tubulars from corrosion and from the salt-driven stresses.
This paper describes the methodology used to design a salt - and CO2 - control cement slurry, the laboratory testing performed to meet the cement requirements and the field implementation of the designed zonal isolation for a well in ultradeep waters of Santos basin. In addition to a salt layer of more than 1,000 m, the challenges for the cement sheath included gas migration and compressive strength retrogression.