A survey of rift basin source rocks

Various studies reveal that rift basins contain a disproportionate amount of petroleum based on their area and sediment volume. In part, this results from the excellent petroleum source rocks found in many of these basins. The presence of these sources not only influences the petroleum potential of the rift sequence, but may also influence the petroleum potential the post-rift succession. These high quality source rocks can be partially explained by the low width: depth ratios and high subsidence rates associated with rift basins. However, not all rifts contain these organic-rich deposits, nor are all the organic-rich deposits volumetrically significant. Other factors, such as climate and sedimentation rate, strongly influence the deposition of these organic-rich sediments. Within individual basins sub-basins may display dramatically different oil- vs gas-prone tendencies due to different subsidence rates. High subsidence rates favour oil source rock development, while low subsidence rates favour gas source development. Many, but not all, of these petroleum source rock systems are lacustrine. Restricted marine source rocks are also present within rift sequences. This study focuses on three elements of rift basin source rocks: (1) their distribution; (2) the factors controlling their deposition, distribution and quality; and (3) their geochemical attributes.