Well integrity is one of the main issues during all life cycles of the well and if any barrier element fails and compromises the integrity of well, remedial strategy may have to be performed to restore the safety and economics of the well. Cement is conventionally used as the isolation material in remedial and primary jobs. However, due to several inherent limitations in cement characteristics, such as cement shrinkage or poor cement slurry compatibility with downhole fluids, it is not always the best solution. Besides these, cement slurry is a particle laden fluid which prevents it penetrating in to tight cracks/pathways to ensure isolation during remedial treatments. This project illustrates the effort to develop a customized polymer as cement alternative and/or cement additive to address challenges posed by conventional cement. Experimental studies are designed to evaluate the characteristics such as rheology, injectivity and mechanical properties of the customized polymer. Furthermore, the compatibility of these polymers with drilling fluids contamination and shrinkage behaviour upon cure are evaluated. Afterward, based on the results of measurements, the limitations of each different formulation are determined and the best formulation is optimized. In addition, the application of the polymer as an additive to conventional cement is studied to optimize some specific properties, such as mechanical properties and permeability. The results of experiments prove that beside the appropriate rheological properties, the polymer provides excellent mechanical properties and much lower shrinkage rate upon cure compared to cement and other systems available in the market. The customized polymer withstands and maintains its properties after being contaminated with considerable volume of drilling fluids and its compressive strength is not much affected by contamination. Also, combination mixtures of customized polymer with conventional cement slurries provide enhanced properties, such as lower permeability and higher compressive strength. The unique characteristics of customized polymer as cement alternative could provide benefits to industry by solving several current challenges in achieving secure isolation. Particularly due to its ability to penetrate in to tight cracks, this customized polymer affords an effective method in to mitigate sustained casing pressure or as a remedial solution for casing leakages which would not be achieved easily by conventional methods.