Geochemical Evaluation of Pinghu Formation Source Rocks for Hydrocarbon Potential in East China Sea of Xihu Depression

Abstract

The Xihu Depression in the East China Sea Basin (ECSB) is a potential petroleum accumulation area, but its Pinghu Formation is poorly understood and requires more geochemical evidence. This study aims to evaluate the organic matter abundance and hydrocarbon potential of source rocks of typical lithologies of mudstone, carbonaceous mudstone and coal. The results show that mudstone source rocks have a broad total organic carbon (TOC) range, with nearly 35% exceeding 1.0% and averaging 1.03%, indicating relatively high organic content. Carbonaceous mudstone and coal and samples exhibit high TOC, ranging from 5.0% to 72.9% and 31.7% to 72.9%, and with average 12.6% and 51.3%, suggesting significant hydrocarbon generation potential. This formation exhibits high organic richness, especially in coal and carbonaceous mudstone, comparable to top source rocks in other Chinese land basins. This supports that mudstone source rocks have a low organic matter abundance and moderate hydrocarbon potential due to their thickness, whereas carbonaceous mudstone and coal showcase higher organic richness with significant hydrocarbon potential. This study provides new geochemical data and insights on the Pinghu Formation and its exploration potential, particularly by enhancing the previously overlooked but noteworthy evidence related to mudstone.