Evaluation Criterion and Methods of the Hydrocarbon Generation Potential for China′s Paleozoic Marine Source Rocks

The evaluation of the hydrocarbon generation potential for the Proterozoic-Paleozoic marine source rocks with the highly maturity to over-maturity in China's marine sediment basins has long been disputed, and there have been no applicable evaluation criteria and methods. The geochemical analyses for low-mature Proterozoic-Paleozoic marine mudstone/shale and carbonatic rock reveal that there are distinctive linear relations between the total organic carbon content (TOC) and generation potential of different types of immature or low-mature Proterozoic-Paleozoic marine source rocks. Judged from hydrocarbon potential of rock pyrolysis, there are no big differences of the lowest TOC threshold (TOC must be greater than 0.5%) for the mudstone/shale and marine carbonate, both of which are regarded as effective potential source rocks. The source rock with TOC value less than 0.75% is poor of hydrocarbon potential for the Proterozoic to the Lower Paleozoic marine source rocks, and TOC 0.75%~1.5%, fair; 1.5%~2.0%, good; 2%~4%, very good; 4%, excellent. The TOC limit of each level for the Upper Paleozoic shale is slightly higher than that of the Lower Paleozoic shale. The initial potential of source rocks with highly or over-maturity in China's Proterozoic-Paleozoic marine sediment basins can be calculated by its TOC and the equations obtained from the immature or low-mature marine source rocks.