Experimental study on the pore characteristics of shale rocks in Zhanhua depression

• Microscopic pore characteristics of shale rock were observed by SEM experiments.
• Organic, intergranular, intragranular pores and fractures were found in shale rock.
• Pore sizes of a shale rock range from 25 to 400 nm, it is less than that of sand rock.
• The movable saturation of mercury in a shale rock is only 0.12.

Special attention has recently been paid to shale oil and gas due to an increase in demand for unconventional hydrocarbons in the worldwide. In 2011, exploration wells were drilled in Bohai Bay Basin, East China, and well production tests for these wells indicate that the oil shale formation has a potential for further oil production. However, pore characteristics of oil shale have not been well understood because of its pore sizes ranging from nanometer (nm) to micrometer (μm), which are quite different from the pore sizes of sandstone reservoir. In this work, scanning electron microscope (SEM) images of shale cores sampled from Luojia formation were used for analysis of micro-pore sizes and structures. Mercury injection experiments were carried out to study pore characteristics and heterogeneity of the shale samples. It is found that the pore types of these shale samples mainly include organic pore, intergranular pore and intragranular pore. Hydraulic fractures and natural micro-fractures are the main types of fractures connecting network in shale rocks. The pore sizes of a shale rock sample from 25 to 400 nm and movable saturation of the non-wetting phase in the rock sample is only 0.12. Both pore sizes and movable saturation in the rock are much less than that of sandstone.

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