Abstract: For long-term abandonment and monitoring of well systems, a series of barriers are formed within a formation and within a casing of a well to prevent materials from leaking from the well. Formation barriers are formed within the formation at the location of perforations in the casing and along the annulus. A series of casing barriers and fluid barriers are formed within the casing of the well. One or more sensors are formed within the barriers to monitor the conditions around the barriers over long periods of time. The sensors can be configured to measure the conditions around the one or more barriers during formation of the one or more barriers and over long periods of time after the one or more barriers are formed.