At the end of life cycle, whether due to low economic return or integrity failure, a series of plugs need to be installed to isolate formations that have sufficient pressure for flowing to the surface or for other adjacent formations and thus ensuring pluging and permanent abandonment. The present work has as objective the use of Rice Bark Ash (RHA) as an alternative material to compose cement paste systems for application in oil well abandonment buffer. Samples containing RHA and reference samples were subjected for seven days at 40 ° C, 80 ° C and 300 ° C, respectively, according to temperature ranges established by the UK Guidelines. The performance of these slurry systems was evaluated for compressive strength (RC) and permeability as an initial assessment of the Portland cement-based materials approval criteria for buffers. TGA and XRD tests were performed to assist in understanding the observed phenomena. The alternative material RHA gave superior or equivalent results in compressive strength under all conditions tested. Another positive factor is that, due to its physical characteristics, it was possible to achieve such performance with higher water addition and lower density than the commonly used pastes. The systems containing RHA presented low permeability values in their hydrated matrix, in some cases being inferior to the reference pastes. Alternative systems have shown promise for composing a well barrier (WB) assembly required to ensure proper abandonment and well integrity even after the end of service life. The system has also proved versatile as it has high performance at both low and very high temperatures, whereas conventional systems need specific compositions for each situation.