Source Rock Characterization Using Seismic Attributes: a Study from the Santos Basin (Offshore Brazil)

Source rocks from the Santos basin pre-salt in Brazil, namely the Itapema and Picarras formations, are characterized based on their total organic carbon content (TOC) with the aid of an acoustic inversion and TOC data from wells. The inverted P-impedance volume is converted into a %TOC volume by applying a formula (empirically derived from well data) that relates P-impedance to TOC. The derived %TOC volume is corrected for compaction in order to compensate for the effect burial has on the P-impedance volume. This %TOC volume aids in the mapping of the source rocks and their extent. It is found that source rocks from within the deeper rift section (where no well data is available) are thicker and that their %TOC increases with depth. A rise in %TOC is indicative of more primary production or better preservation potential (more anoxic conditions) at the time of deposition. Deposition rates for the source rock and subsidence must have been higher in the depocenter of the lower syn-rift in order to account for the thicker source rock deposits.