Salt-Tolerant Cement Systems to Mitigate Gelling Effect

Abstract A number of reservoirs around the globe are deep, and often it is necessary to drill and cement through salt zones to reach the reservoir section. Brazil offshore is one example where reservoirs are buried deep, and the salt zones there are quite challenging to drill through and cement. Many of these salt zones contain chemically reactive salts, such as magnesium and calcium chloride, and usually pose unique challenges during placement of the slurry and subsequent cement slurry hydration and compressive strength development. These salts, especially MgCl2, chemically interact with the cement slurry, thereby altering the mechanism and kinetics of cement hydration, leading to premature gelation and shorter thickening times. Mitigating these effects is a challenge and is important to successfully place the cement slurry in the annulus and for the slurry to develop the required mechanical properties, such as compressive strength. In the present study, slurries were formulated to overcome gelation issues with the required compressive strength for successful zonal isolation. The slurries were designed in such a way that they can take up to 12% contamination by weight of water (bwow) of the MgCl2-based salts known as carnalite and tachyhydrite. Pertinent data that characterize performance of these slurries are presented in this paper.