Potential of lacustrine source rock in the pre-salt depression stage and its geological significance in Santos Basin, Brazil

About the lacustrine source rocks in the pre-salt of Santos Basin, the present exploration confirms that the lacustrine source rocks of Picarras (PIC) Formation - Itapema (ITP) Formation in the pre-salt rift period are high-quality source rocks. Due to the lack of drilling data, it is difficult to confirm whether the high-quality of lacustrine source rocks are developed in Barra Velha (BV) Formation. To clarify the development characteristics of the source rocks in the pre-salt depression stage (BV Formation development period), the paleogeography, paleoclimate,and paleo-water environment of BV Formation in the depression period of the basin were restored using paleobiology and geochemistry data. It is considered that the BV Formation in the depression period was a wide shallow saline lake. Under the arid climate background, it was easy to form salinity stratification; and an anoxic environment was formed at the bottom of the lake, which was beneficial to the preservation of organic matters. Geochemical analysis showed that during the deposition of BV Formation, volcanic activities around the basin were frequent, and multiple transgression occurred, which brought rich nutrients to the lake water and was conducive to the growth of algae. Sufficient material and favorable preservation conditions for organic matters benefited to high-quality source rocks development. At last, the development model of lacustrine source rocks in the pre-salt depression was established, which provided new direction to the exploration to the source rocks in the depression stage of Santos Basin.