Occurrence State of Soluble Organic Matter in Shale Oil Reservoirs from the Upper Triassic Yanchang Formation in the Ordos Basin, China: Insights from Multipolarity Sequential Extraction

Multi-Isothermal Stage Pyrolysis of the Chang 73 Shale Oil Reservoirs, Ordos Basin: Implications for Oil Occurrence States and In Situ Conversion Exploitation

“…The only outlier in the regression analysis was sample 7 of MS (Figure a–f). The same phenomenon also occurs in the study by Li et al (the samples were consistent with those in this study), which was caused by the particularity of MS relative to DM, BS, and FS. In particular, MS has the transitional characteristics of source rocks and reservoirs because of its certain OM content .…”

“…Shale oil mobility is determined by the coupling relationship between pore space and oil-phase states in which the occurrence state is the key factor, and there is a current consensus that oil in the free state is the main contributor to shale oil productivity. , Hence, the quantitative characterization of shale oil in different occurrence states is of great significance of the shale oil mobility and recoverability evaluation. The shale oil phase mainly depends on its component and its relationship with the peripheral medium. ,, For the pyrolysis experiments in this study, the occurrence states of the thermally released EOM can be roughly judged by their component features and differences. For the Mu&Sh samples, the main carbon of OM components from EOM-1 and EOM-2 was C 15 –C 17 , and the carbon number range was from C 12 –C 31 , mainly light compounds, which belong to free hydrocarbons (Table and Figure ).…”

“…With the continuous generation of hydrocarbons, the content of small molecular organic components increases. When the hydrocarbon production and pressure reach the key point, they will be discharged from the source rock to start the secondary migration to the upper and lower superimposed Si&Sa . Si&Sa only features the storage of hydrocarbons, in which hydrocarbons were discharged and migrate from source rocks and are chiefly light to medium components such as saturates and aromatics .…”

“…Approximately 300 g of eight core samples was intercepted first, crushed to approximately 200 mesh, and equally divided into three parts for TOC analysis, Soxhlet extraction, and component fractionation as well as mineral composition determination. A LECO CS230 carbon/sulfur analyzer was used to determine the TOC content of the first part of the powder samples, and the specific experimental process was performed according to Li et al The second part of the powder sample was Soxhlet-extracted with chloroform for 72 h and weighed once the solvent evaporated completely. The ratio of the extracted hydrocarbon mass to the original powder sample mass was defined as the whole-rock soluble OM content to evaluate the residual bitumen and retained oil content of different lithologies.…”

“…The states of shale oil can be divided into three states: free, adsorbed, and miscible states. , Shale oil in the free, adsorbed, and miscible states is mainly composed of small molecular components with good fluidity, medium-macromolecular components with poor fluidity, and medium-to-small molecular components, respectively . Structural fractures, bedding fractures, microfractures, and nanomatrix pores of clay minerals, quartz, feldspar, calcite, dolomite, and other minerals exist in the free state; on the mineral surface, the interlayer structure of clay minerals and the internal and external surfaces of kerogen form a rigid macromolecular framework by physical adsorption and noncovalent chemical adsorption for the adsorbed state and in the internal network of kerogen as the enveloped small molecular mobile phase as well as in the asphaltene and residual water as the dissolved form for the miscible state .…”