| Shale gas has enormous resources and potential, and has gradually become an important growth point of
natural gas industry in China. Shale gas reservoirs are characterized by complex mineral compositions, multi-scale pore,
various gas storage spaces and modes of occurrence, and strong heterogeneity. Shale pores can be divided into inorgaric
pores and organic pores. Inorganic pores are mainly composed of intergranular or intragranular pores of mineral particles
such as quartz, feldspar and other minerals. The pore size is mainly micrometer scale, and the pore surface has water-wet
characteristics. Organic pores are mainly nanoscale and exist in the organic matter of shale, with high specific surface area
and oil-wet pore surfaces. Methane in shale gas reservoir has three occurrence states: free gas in inorganic pores, free gas
and adsorbed gas in organic pores. Accurate volume measurement of gas with different occurrence state can provide
important basic data for resource evaluation of shale gas reservoir. Based on the differences of wettability and pore size
between shale inorganic pores and organic pores, and considering the different storage locations of methane, helium and
water in shale inorganic pores and organic pores, experimental measurement and calculation methods are presented to test
gas volume of different occurrence states under reservoir temperature and pressure conditions, and shale inorganic
porosity and organic porosity are also obtained. On this basis, the influencing factors of gas content in shale gas reservoir
are analyzed. The results show that for the selected rock samples, inorganic pores and organic pores account for 65% and
35% of the total pore volume respectively, and the free gas in inorganic pores, free gas in organic pores and adsorbed gas
account for 51%, 22% and 27% of the total gas content on average respectively. The shale of the Lower Silurian
Longmaxi Formation in southern Sichuan has a high degree of thermal evolution. With the increase of the total organic
carbon content, a large number of nanoscale organic pores are developed, providing adsorption space for methane. It is
clarified that the total organic carbon content mainly affects the content of adsorbed gas. It is pointed out that in the
evaluation of shale gas resource quantity, production capacity prediction, and later development process, the influence of
organic matter and its internal adsorbed gas needs to be considered. |
