A crack and fluid containment collar and system for well casings to prevent micro-annulus crack propagation and fluid flow therethrough. The collar includes an annular wall extending coaxially from a first end thereof to form a trough around a casing on which the collar is disposed. A plurality of circumferential channels is provided in an exterior surface of the collar and an interior surface of the annular wall. Pairs of the collar are coupled to the casing in opposite orientations; one above and one below a containment zone with their annular flanges directed toward the zone. When encased in cement, the collars impede propagation of cracks (and fluid/gas flow therethrough) along the surfaces of the casing and collars. A second end of the collar is tapered to direct crack formation away from the collar and casing.