Pore characterization of shale in Shanxi Formation, Yan'an area, Ordos Basin

The shale reservoirs in the Upper Paleozoic Shanxi Formation in the Yan'an area of the Ordos Basin were studied. The whole porosity of the shale was characterized in detail using NMR, SEM, high pressure mercury intrusion, nitrogen adsorption and carbon dioxide adsorption. The Shanxi Formation in the Yan'an area mainly developed four types of porosity, i.e. fractures, intergranular, intragranular pores, and organic pores, with intragranular and organic pores in the majority. The T₂ NMR curves are mostly single-peaked and almost unchanged after centrifugation, indicating that the samples are dominated by nano pores with poor connectivity. High pressure mercury intrusion, nitrogen adsorption and carbon dioxide adsorption experiments showed that the pore volume is mainly meso pores and macro pores, accounting for about 85% of the total pore volume, while micro pores only account for 15% of the total pore volume. The specific surface area is mainly provided by micro pores and meso pores, with micro pores accounting for 52% of the total specific surface area, followed by meso pores accounting for 48%. Macro pores can be neglected when the surface area is more than 99%. The pore morphology of the samples is mainly parallel plate pores with openings or slits at both ends.