Different innovative experimental and numerical methods are presented to assess strategies and materials susceptible of significantly improving well cementing, remediation of fractured cement sheaths and permanent well plugging. The methodology developed has two aims: the first is to test and model most realistic and relevant conditions, to probe and prioritize the issues in cementing and remediation; the second aim is to thereafter propose the best and most cost-effective solutions and test them for worst-case situations. Experimental techniques involve testing the cement to formation interface tensile strength, cement sheath integrity under casing cyclic pressure, remediation fluid sealing testing on controlled fractures and numerical simulations of improved well plugging. Care is taken to include as relevant as possible stress and pore pressure conditions in these tests, both when preparing the cement sheath and when testing integrity and remediation scenarios. The interface strength tests revealed the weakest link in the system and thus suggested a strategy of combining different stiffness of cement as a way to improve the sealing efficiency around the well. This strategy was explored numerically in the case of a cement well plug, suggesting an efficient but cost-effective method to abandon oil and gas or CO2 injection wells.