New Horizons of Well Bonding: Cement Expansion in Absence of Water Access

Zonal isolation for primary cementing is generally of concern when there is potential for gas migration. The challenge for the industry is to achieve a long-term annular cement seal and prevent gas migration. This paper focuses on the problem of ensuring sufficient bulk expansion of set cement without access to external water and optimizing the cement slurry formulation. The approach to solving this problem is creative and simple within the industry. One of the reasons for wellbore gas migration and inter-connected flows can be due to cement shrinkage over time. This study focuses on laboratory testing of an expanding cement system in the absence of water and analysis of test results of novel the cement system in terms of its implementation on well with high gas migration potential. The cement system behavior will also be described in terms of rheological, filtration and mechanical properties and compared to conventional expanding cement slurries. This approach can be used to improve cement bonding with the aim of minimizing future remedial jobs. Several approaches were implemented to achieve noticeable expansion in anhydrous media. One of the methods showed it was feasible to achieve 1.27% linear expansion in set cement without external water contact, while linear expansion in the presence of water was 0.78%. This method uses the addition of sodium chloride (NaCl) and while it has been previously described in literature, no practical design/testing directions have been given. The study identified the most effective concentration of sodium chloride required for set cement expansion without water availability. The study described how other cement system properties permitted better results in terms of placement quality of highly salt-saturated cement. Overall, complex laboratory test results provide evidence of effective linear expansion in set cement in the absence of external water. The optimization of cement slurry properties was focused on obtaining optimal thickening time, rheology and compressive strength, which was complicated by the presence of a high concentration of sodium chloride. An expanding cement system was successfully tested in the absence of water showing positive linear expansion. A new approach for testing expanding cement systems in the absence of water was introduced how excessive linear expansion could be compromised with compressive strength development. The research results have shown that the use of NaCl additive in high concentrations in high SVF self-healing systems provided improved performance when aiming for effective linear expansion in set cement in the absence of water.