Long-term zonal isolation is an important factor to consider while designing cement slurries for deep high-pressure, high-temperature (HPHT) gas wells. Conventional heavyweight cement systems used in the past have often had to sacrifice set cement mechanical properties, such as compressive strength, permeability, and porosity, to provide a stable, mixable, and pumpable slurry design.

Changes in downhole conditions in terms of temperature and pressure can induce sufficient stresses to destroy the integrity of the cement sheath, causing long-term gas migration and sustained annular pressure. Hence, the set cement mechanical properties have to be carefully designed in order to withstand the downhole stresses, especially the ones generated from well testing.

A novel flexible and expanding cement system was chosen for the eighth well of project in Saudi Arabia.