Multifunctional Cementing Additives, A Way to Improve Rig Time Saving and Annulus Fluid/Gas Migration During Cement Placement

Abstract

Controlling gas migration in the annular space during cement placement involves several challenges; especially in deep wells where temperature contrast leads to longer wait-on-cement (WOC) time, widening the window where fluids can migrate. Such extended setting is caused by the lower temperature in upper sections which impacts compressive strength build-up while also leads to higher rig time costs. In this paper, the authors focused on key aspects of slurry design to minimize these problems. Among the factors that contribute to the invasion and migration of gas and other fluids into the annular space, are insufficient hydrostatic pressure, poor slurry design, inefficient mud removal, problems during cement hydration, or defective cement-formation-casing bonding. For this study, an experimental method was followed to evaluate specific additives and their impact in gas control performance. Different slurry formulations were evaluated at a temperature range between 50°C and 110°C (120°F -230°F) while pressure kept at 5300 psi to minimize variables. The laboratory evaluation included tests for determining thickening time, rheology, compressive strength, fluid loss and gas migration. The slurry design involved the use of a novel retarder based on synthetic polymer with carboxylic acid functionality as well as a colloidal silica dispersion. The results showed that the selected additives allowed the slurries to achieve the targeted thickening time with a right-angle set, a short transition time and quick build up in compressive strength. In addition, the migration tests indicated excellent gas control under evaluated conditions. The studied additives performed well individually and even better combined, with a synergistic effect when preventing gas migration and accelerating compressive strength build-up. The additives evaluated showed multifunctional attributes that are beneficial not only to prevent gas migration and retard slurry setting, but also to accelerate compressive strength, a cement feature which allows significant savings in rig time costs.