Methods of characterizing the self-healing properties of a set cement based material in contact with hydrocarbons in an oil- and/or gas-well are described. The methods comprise: providing a test cell (10); providing said test cell (10) with a sample (31, 40) of the set cement based material; damaging the sample to simulate a loss of zonal isolation resulting from damages made to the set cement based material in the oil- or gas-well; injecting a hydrocarbon fluid in the test cell; allowing the cement based material to heal by itself; measuring the differential pressure (ΔP) across the sample (31, 40); and characterizing the self-healing properties of the cement based material from the measure of said differential pressure (ΔP).