## 4 Characteristics of Low-Resistivity Shale Reservoirs
### Microscopic Pore Structure Characteristics of Low-Resistivity Shale Reservoirs  
Shale, as an unconventional reservoir that integrates source and storage, continuously generates natural gas through the thermal evolution of organic matter inside. Natural gas enriches in the internal storage space of shale after short-distance migration or no migration. The organic pore morphology of low-resistivity shale gas reservoirs in the Luzhou area is mainly circular elliptical pores, with rare irregular pores. There are many organic pores, but the pore size is small, ranging from 0 to 50 nm. Organic pores exist in isolation and have poor connectivity between pores (Figure 4a-c). In normal-resistivity shale reservoirs, organic pores are highly developed and have good connectivity, mostly consisting of sponge-shaped bubble pores and honeycomb-shaped pores, with pore sizes generally exceeding 100 nm (Figure 4d-f). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & **Section** & **TOC (\%)** & **Ro (\%)** & \begin{tabular}{c} **Quartz** \\ **Content** \\ **(\%)** \\ \end{tabular}  & \begin{tabular}{c} **Clay** \\ **Content** \\ **(\%)** \\ \end{tabular}  & \begin{tabular}{c} **Pyrite** \\ **Content** \\ **(\%)** \\ \end{tabular}  & \begin{tabular}{c} **Porosity** \\ **(\%)** \\ \end{tabular}  & \begin{tabular}{c} **Water** \\ **Saturation** \\ **(\%)** \\ \end{tabular}  & \ \begin{tabular}{c} **Gas** \\ **Content** \\ **(\%)** \\ \end{tabular}  \\ \hline Low Resistivity &
\begin{tabular}{c} 1–3 sub \\ layer \\ 4 sub layer \\ 1–3 sub \\ 1–3 sub \\ 1–3 sub \\ 1–3 sub \\ 1–3 Reservoir \\ 1–3 sub \\ 1–3 Reservoir \\ 1–3 sub \\ 1–3 sub \\ 1–3 Reservoir \\  
The pore structure parameters of shale reservoirs in the study area were quantitatively tested using high-pressure mercury intrusion and liquid nitrogen adsorption. The results revealed that the total pore volume in low-resistivity shale reservoirs is smaller than that in normal-resistivity shale gas reservoirs (Figure 5a). The pore volume of each well of 1-3 sub layers in the study area ranges from 0.0117 to 0.0205 cm\({}^{3}\)/g, with an average of 0.0164 cm\({}^{3}\)/g. Among them, the average pore volume of low-resistivity shale gas wells (Well Y101H88-1, L211, and Y101H91-4) of 1-3 sub layers are 0.0140 cm\({}^{3}\)/g, 0.0136 cm\({}^{3}\)/g, and 0.0158 cm\({}^{3}\)/g, respectively, with a total pore volume of relatively low. In the shale reservoir of a normal-resistivity shale gas well, the average pore volume for the 1-3 sub layers are 0.0183 cm\({}^{3}\)/g, reflecting a notably high pore volume. Within the low-resistivity shale reservoir, the shale samples from Well Y101H91-4 exhibits the most significant pore specific surface area, while the 1-3 sub layers boat an average pore specific surface area of 18.76 m\({}^{2}\)/g. Conversely, the samples from Well Y101H88-1 possess the least pore-specific surface area among the low-resistivity shales, averaging 11.31 m\({}^{2}\)/g. On the whole, the specific surface area in low-resistivity shale reservoirs is greater than 10 m\({}^{2}\)/g (Figure 5b). In normal-resistivity shale reservoirs, the average specific surface area of pores is between 8.63 and 11.76 m\({}^{2}\)/g, with an average value below 10 m\({}^{2}\)/g. The bar charts depicting the full pore size distribution within the shale reservoirs of normal-resistivity wells (Well Y101H10-3, Y101H3-8, and L210) reveal a broad range of pore sizes, characterized by two primary peaks at 1-6 nm and 10-50 nm, respectively (Figure 6a-c). Shale gas wells with low-resistivity, including L211, Y101H88-1, and Y101H91-4, exhibit less developed pores and smaller pore sizes compared to normal-resistivity wells. The pore volume-pore size distribution histogram reveals a predominantly single peak for the pore sizes in these low-resistivity wells, with the peak range being narrower than 10 nm (Figure 6d,e). Figure 5: Histogram of pore volume and specific surface area of shale in 1–3 sub layers in Luzhou area.