Impact of Hydrothermal\nFluids on Hydrocarbon Generation\nand Solid Bitumen Formation in the Kongdian Formation, Huanghua Depression,\nChina

Hydrothermal fluid\nplays a crucial role in the generation and migration\nof hydrocarbons within sedimentary basins. Herein, we employed bulk\nanalysis and high-resolution mass spectrometry techniques to investigate\nthe transformation dynamics from source rock to hydrocarbons under\nconditions influenced by magmatic activities in the Kongdian Formation,\nHuanghua Depression, China. The results revealed that hydrocarbon\ngeneration in the Ek<sub>2</sub> shale of the study area was significantly\ninfluenced by abnormal heating from hydrothermal fluids. High temperatures\nassociated with these fluids accelerated the conversion of organic\nmatter within source rocks, enhancing hydrocarbon generation rates.\nSubsequently, the hydrocarbons migrated into fracture networks, where\nthey solidified as low-reflectance solid bitumen, forming trapped\nfractures of pyrobitumen and authigenic mineral aggregates leached\nfrom thermal fluid. High aliphatic fractions were noted in the source\nrock extracts, while extracts from low-reflectance solid bitumen exhibited\nhigher aromatic fraction. Aliphatic and aromatic compounds in extracts\nfrom both the low-reflectance solid bitumen and the source rock exhibited\nsimilar maturities and origins. Regarding polar compounds, the compound\nclasses O<sub>1</sub>, O<sub>2</sub>, N<sub>1</sub>O<sub>1</sub>,\nand N<sub>1</sub>O<sub>2</sub> showed higher abundances in source\nrock extracts compared to those in low-reflectance solid bitumen,\nwhile the S<sub>1</sub> and N<sub>1</sub> classes showed the opposite\ntrend. Thus, fractionation clearly occurs when hydrocarbons expelled\nfrom source rocks by thermal fluids solidify into low-reflectance\nsolid bitumen. This unique study provides valuable insights into understanding\nthe fate of hydrocarbons originating from source rocks heated by thermal\nfluids, and explores the potential for unconventional oil in regions\nwith intense hydrothermal alteration.