Study on the Influence of Shale Storage Space Types on Shale Gas Transport

Shale gas is an important unconventional natural gas resource. Studying the microstructure of shale and the gas transport law is of great significance for the development of shale gas. This paper uses the field emission scanning electron microscope to observe shale samples of the BC shale gas reservoirs in southern China. It is found that there are three types of storage spaces on the micro-nano-scale of shale samples. The storage space can be distributed either in pure organic matter or pure inorganic matter or in both organic matter and inorganic matter. They are called organic storage space, inorganic storage space, and mixed storage space of organic matter and inorganic matter, respectively. According to these types of storage spaces, an ideal conceptual model that reflects various types of storage spaces has been researched and established on the micro-nano-scale. At the same time, the transport mechanisms of slip, diffusion, adsorption, and coupling have been considered, and shale mixed storage space has also been considered in particular. On this basis, a comprehensive equation that can simulate the transport of shale gas in various types of storage spaces is derived. The equation also introduces the proportional parameters of the organic part, fractal characteristics, and water film of the inorganic part in the mixed storage space. Researchers can adjust this parameter to simulate shale gas transportation in different types of storage spaces and then use the finite element method to solve it numerically. This paper analyzes the influence of shale reservoir space types on shale gas transport. The larger the proportion of organic components in the mixed pores, the better the gas transport. The rough fractal dimension of the pores also affects the gas transport. However, when the pore diameter is less than 300 nm, the rough fractal dimension of the pores has a negligible influence on gas transport. For the water film on the inorganic wall surface of mixed pores, the gas transport of the macropore is more sensitive to the change in water film thickness.