Genesis of deep lacustrine subfacies laminated shale and influence factors on shale oil mobility in Cangdong sag,Bohai Bay Basin
The laminae,the fundamental sedimentary structure of deep-lacustrine subfacies shales,have an important influence on the mobility of shale oil.This paper is a case study of the Member 2 of Kongdian Formation in Cangdong sag of Bohai Bay Basin.Com-prehensively using the testing techniques such as X-ray diffraction,Rock-eval,X-ray fluorescence spectra,advanced mineral identifi-cation and characterization system,high resolution field emission scanning electron microscopy,and N2 adsorption,the paper ex-plores the features and genesis of laminated shale oil at the micro-and nano-scale,and deeply analyzes the controlling factors of shale oil mobility.The results show that there are mainly five types of laminae in the study area,i.e.,felsic laminae,calcareous-dolomitic laminae,clayey laminae,analcime laminae,and mixed laminae.The average thickness of felsic,lime-dolomitic and clayey laminae is approximately 250 μm,125 μm,and 65 μm,respectively.These laminae mainly develop three types of laminated shales,i.e.,lami-nated felsic shale,laminated calcareous-dolomitic shale,and laminated mixed shales.The classification of organic facies based on fine-grained sedimentation indicates that laminated felsic shale originate from freshwater depositional environment with strong exter-nal input,whereas laminated calcareous-dolomitic shale are formed in saline water depositional environment of sulfur-rich carbonate and evaporite.This reveals the differences in efficient hydrocarbon generation mechanisms between laminated felsic and calcareous-dolomitic shales.The further research suggests that the mobility of shale oil is jointly affected by both organic and inorganic geolog-ical factors.The conditions favorable for the mobility of shale oil is as below.(1)Shale has the moderate total organic carbon con-tents in the range from 1％to 4％,with the maximum pyrolysis temperatures in the range from 435 ℃ to 450 ℃.(2)Gas-producing kerogen is developed in shale,rather than oil-producing kerogen.(3)Shale possesses higher carbonate content compared to felsic content,large pore diameter,and low pore specific surface area.This study is expected to improve the evaluation of"sweet spots"in continental shale oil and guide shale oil exploration and development.
laminaedeep lacustrine subfaciesshale oilCangdong sagBohai Bay Basin
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