Determination of the thicknesses of oil films in micro- and nano-pores in tight oil sands: an example from the southern Songliao Basin, NE China

Abstract

An experimental method of field-emission environmental scanning electron microscope (ESEM) coupled with the energy dispersive spectrum (EDS) to determine the thickness of oil films in the micro- and nano-pores of tight oil sands was proposed to overcome the limitations of current methods. First, we got the data of the detection range volumes, elemental mass percentages, and elemental atomic percentages using the EDS, and then calculated the volumes of oil films in the detection range according to the elemental mass percentages and the elemental atomic percentages of carbon. After that, we calculated the surface areas of oil films using the pore size data (lengths, widths, and depths) detected by ESEM. The thicknesses of oil films in the pores equaled the volumes divided by the surface areas. An analysis of tight oil samples from the Quan 4 Segment of in the southern Songliao Basin, NE China confirmed that the oil in the micro- and nano-pores had two main forms: oil films and oil droplets. The thicknesses of the oil films ranged from about 400 nm to 2 μm, while the thicknesses of the oil droplets ranged from about 200 to 700 nm.