Characteristics of pore structures in Paleogene shales in Nanpu Sag

Key words:  Nanpu Sag  shale pore structure  Nanopores  adsorption

Abstract:

Using rock pyrolysis, X-ray diffraction mineral analysis, electron microscopy scanning, and nitrogen adsorption tests, this research studied and discussed the pore structures in Paleogene shales in Nanpu Sag. The new results show that Nanpu Sag shale reservoir can be characterized as the follows. It is of low porosity and tight; and part of the samples have high content of brittle minerals, which can be easy to form a fracture network. The microscopic pore types are organic, intergranular, intragranular and microfracture. Micropores and mesopores provide most of the pore surface area and pore volume, which are the main space for shale gas adsorption and storage. Pore structures include ink-bottle-like and slit-like pores, of which ink-bottle-like pores are the main pores favorable for gas absorption. The TOC content is the main internal factor that controls the volume and surface of nanopores of the Paleogene shale gas reservoir in Nanpu Sag. Quartz has good correlation with pore volume. Brittle mineral has a positive effect for the construction of the pores. Lastly TOC is the main factor affecting shale methane adsorption capacity.