Shale oil occurs in free state （including condensate state）, adsorption state （adsorbed on kerogen and mineral particles） and dissolved state （dissolved in natural gas, residual water, etc.） in shales and adjacent layers. The characterization of the occurrence of different hydrocarbons in shale oil, especially the quantitative separation of free hydrocarbons （mobile oil）, has been the current focus of shale oil research. Taken the shale oil from the Muli coalfield in Qilian Mountain as an example, this work extracted shale samples with organic solvents of different polarity to obtain different occurrence states of hydrocarbons in the oil-bearing shale and to reveal the compositional differences of the hydrocarbons. The result may provide new geochemical information for the occurrence and mobility of shale oil.
The gas hydrates in the permafrost region of Qilian Mountain are characterized by low latitude, thin thickness, shallow burial depth, abundant coal seams, high contents of heavy hydrocarbons and multiple sets of source rocks. Up to date, the source of gas or the main source rocks of the Mull gas hydrates have remained unclear.
As an important part of gas hydrates, light hydrocarbons （LHs）, especially C5 to C7 hydrocarbons with various monomer compounds, provide a wide variety of geological and geochemical information, which have received much attention from organic geochemists and petroleum geologists.
Previous work has largely discussed the relations between sediment structures and accumulation of gas hydrates in the Shenhu area of South China Sea, but has not documented why the gas hydrates occurred at the seafloor topographic highs. Many gas hydrate exploration examples abroad also indicate that the saturation of gas hydrates was higher at seafloor topographic highs. This work aims to understand why gas hydrates accumulated at topographic highs and why their saturation is higher.
