Pore characteristics and its impact on shale oil occurrence of lacustrine shale from Chang 7, Ordos Basin

The shale pore development characteristics is of significant impact on the occurrence quantity, state, pore size, and mobility of shale oil. In order to study the relationship between the development of nanoscale pores in lacustrine shale and the shale oil occurrence, nineteen Chang 7 shale samples were conducted to geochemical, mineral composition, FE-SEM and N2 adsorption analysis, and the results show that: pore types include microfracture, intercrystalline pores of clay matrix, and intergranular pores of detrital minerals. All samples can be classified into three categories based on the N2 adsorption pore structure characteristics, and mainly develops narrow slit shaped pores, accompanied by relatively developed micropores. The pore development is correlated with the quartz, kaolinite, and chlorite, and the illite and I/S mixed layer is also important carrier for narrow slit shaped pore development. Statistical analysis of S1 and pore volumes within specific pore diameter range show that 13.947 and 50 nm may be the lower limit of the pore diameter for residual free oil and free oil with better fluidity, respectively. This study provides a reference for the coupling relationship between shale pore structure and shale oil occurrence and the quantitative characterization of the pore size lower limit of free oil.