Hydrocarbon generation and potential in continental organic-rich shales at the highly-mature stage, as determined by hydrous pyrolysis under supercritical conditions

Abstract

Hydrous pyrolysis experiments were conducted to assess hydrocarbon generation and potential in three continental organic-rich shales at the highly-mature stage. The results of this study have important implications for deep petroleum exploration in China. The calcareous shale dominated by type-I kerogen reached its peak oil generation at a vitrinite reflectance (VR) of 1.5 %Ro, and entered the major stage of gas generation at a VR ranging from 1.50 to 2.44 %Ro. The high HI, low S2 and low atomic H/C ratio revealed that the calcareous shale has some potential for hydrocarbon generation at a VR greater than 2.44 %Ro. The mudstone with type-II kerogen reached its peak oil generation at a VR of 2.5 %Ro. The high atomic H/C ratio, but low HI and S2 indicated that mudstone may retain some hydrocarbon potential. The carbonaceous mudstone dominated by type-III kerogen had still not reached its peak of hydrocarbon generation at a VR of 3.12 %Ro. The low dryness of the gaseous hydrocarbon yields shows that the carbonaceous mudstone was still in the primary gas generation stage. The high values of S2 and atomic H/C fraction, but low HI, revealed that the carbonaceous mudstone may retain a large hydrocarbon generation potential at higher maturity stages. Our results suggested that the continental type-I and -II kerogen may have potential for shale gas and deep petroleum generation, while the continental type-III kerogen retained good potential for yielding deep natural gas.