The upper Paleozoic Marine shale in middle Guangxi Depression

namely Guizhong Depression

has experienced complex tectonic evolution and thermal evolution. As the main production layer of shale gas

the microscopic pore structure characterization and reservoir pore evaluation of the shale in lower Carboniferous need to be studied urgently. Focus on the Lower Carboniferous Luzhai Formation shale reservoir in the northern Guizhong Depression

the material composition and reservoir pores of the shale are characterized and

evaluated in detail by rock thin section

scanning electron microscope

Xray diffraction

porosity and isothermal adsorption tests on samples both from fields and cores. The results show that the

TOC

in the shale of Luzhai Formation is 0.4 % ~ 6.6 %. The organic matter is in the stage of high mature to over-mature thermal evolution. The content of brittle minerals such as quartz is high

with a good fracturing ability. The shale in Luzhai Formation

with an average porosity of 2.91 % and an average permeability of 0.007 9 ×10

-3

μm

2

is a kind of low porosity

ultra-low permeability and good breakthrough pressure shale gas reservoir. There are five types of pores in the shale reservoir: the residual intergranular pore

intergranular pore

intragranular dissolved pore

clay minerals interlayer pore and organic pore. The main contributors are the clay minerals interlayer pores

the organic pores and the pyrite intergranular pores. The aperture rangs from 17 nm to 65 nm

most of which are microporous or mesoporous with the scale less than 50 nm. The connectivity between the pores is poor and there is a certain connectivity inside the pores.