## 4 Result
### Pore Type and Morphology
#### 4.2.3 Intragranular Pores  
Two distinct types of intragranular pores have been observed in the Funing Formation shale of the Gaoyou Sag. One category consists of intergranular pores that form between clay minerals and pyrite crystals arising from loose aggregation during their growth mechanism. The intercrystalline pores found within clay minerals demonstrate a wide variety of shapes, encompassing triangles, quadrilaterals, and ellipses. The observed pores demonstrate a broad range of sizes, varying from a few nanometers to several hundred nanometers, with a smaller portion extending into the micron scale. On average, these pores measure in the tens of nanometers. (Figure 5a). Observations conducted using a field-emission scanning electron microscope have revealed the presence of both individual pyrite monomers and aggregates within the shale of the Funing Formation in the Gaoyou Sag (Figure 5b). In the pyrite monomer, the presence of minuscule punctiform depressions can be observed, whereas in the pyrite aggregate, intergranular voids are predominantly  
Figure 4: SEM image of intergranular pores of Funing Formation shale in the Gaoyou Sag. (**a**): Intergranular pore, L-2. (**b**) Intergranular pore, L-5.  
Figure 3: BSE image of organic-matter pores in the Funing Formation shale in the Gaoyou Sag. (**a**) Organic matter pores, L-1. (**b**) Organic matter shrinkage joint, L-5.  
present. The intergranular pores display an irregular polygonal morphology, characterized by dimensions spanning from tens to hundreds of nanometers, with an average size in the tens of nanometers.  
The majority of the intergranular pores present in the pyrite are filled with organic matter and various inorganic minerals. A portion of the intergranular pores, which are located between loosely accumulated pyrite aggregates, are unoccupied. The shale reservoir in the study area exhibits a low pyrite content, with an average of only 2.72%. Consequently, the influence of pyrite on the intergranular pores within the shale reservoir's overall pore structure is relatively modest.  
The second category of pores comprises dissolution pores, which are created by the dissolution of unstable minerals such as calcite, quartz, and feldspar as a result of the influence of organic acids released during the thermal transformation of organic matter [33]. These dissolution pores are predominantly isolated and densely distributed in circular or oval shapes (Figure 6). These materials demonstrate a relatively limited distribution of pore sizes, typically measuring in the tens of nanometers, on average. Additionally, they exhibit suboptimal connectivity between pores.  
The current state of the Funing Formation shale located in the Gaoyou Sag is characterized by thermal catalytic oil and gas generation. The substance exhibits a notable concentration of organic acids and a significant abundance of soluble minerals. The mineral composition of the sample consists of carbonate minerals, which make up a varying percentage between 12% and 62.4%, with an average of 37.9%. Additionally, silicate minerals are present, accounting for proportions ranging from 23% to 55.1%, with an average of 39.3%. As a result, a significant quantity of dissolution pores have formed within the shale reservoir in the examined region.  
Figure 5: SEM image of intergranular pores of the Funing Formation shale in the Gaoyou Sag. (**a**) Intercrystalline pores of clay minerals, L-1. (**b**) Intergranular pores of pyrite, L-4.  
Figure 6: SEM image of dissolution pores in the Funing Formation shale in the Gaoyou Sag. (**a**) Corrosion pore, L-3. (**b**): Corrosion pore, L-6.