This paper is the result of oil and gas exploration engineering.

Objective The pore size distribution of shale reservoirs is a key factor affecting the occurrence of shale gas, and clarifying the pore size distribution characteristics of shale is the basis to study the law of shale gas enrichment.

Methods By a case study of the Gufeng Formation shale in Well WWD-1, this paper studies the pore size distribution characteristics of the Gufeng Formation shale in the Lower Yangtze region by means of XRD, organic geochemical, high pressure mercury injection, N₂ adsorption and CO₂ adsorption experiments, and further discusses the effect of pore size distribution on the gas-bearing properties of shale.

Results The shale of the Gufeng Formation has an abundance of organic matter, and TOC is between 2.72% and 6.71% which has a good potential for hydrocarbon generation. The pore size distribution of Gufeng shale is complex, with micropores, mesopores and macropores widely developed. However, the pore volume of Gufeng shale is mainly contributed by mesopores, and the contribution rate of mesopores is 50%–68%. The hydrocarbon generation and evolution of organic matter provided a large number of micropores and mesopores for the shale of the Gufeng Formation. Clay minerals mainly developed micropores, and carbonate minerals were important for the development of macropores. Micropores and mesopores control the development of specific surface area of shale reservoirs, while mesopores and macropores have an important influence on the total pore volume. The development of micropores and mesopores is conducive to the occurrence of adsorbed gas and increases the preservation of internal gas. The development of mesopores and macropores can provide space for free gas and increase the total gas content. In the areas of structural stability, mesoporous and macroporous reservoirs can be used as advantageous exploration targets, but in complex structural areas, mesoporous reservoirs have an advantage.

Conclusions The Gufeng Formation shale is located in the complex structural area of the Lower Yangtze. The pore types are mainly mesopores, with characteristics of mixed enrichment of adsorbed gas and free gas. The Gufeng Formation shale has a certain ability of anti-leaking under the guarantee of the total gas content, which is a target as the main layer of shale gas exploration and development in the Lower Yangtze.