## 4 Results and Discussion
### Pore Fluid Evaluation  
By integrating gradient temperature drying with high-speed centrifugation, the pore fluid types within the deep-marine shale reservoir were quantitatively classified [39]. As the centrifugal speed increased (Figure 8A), the decreasing trend of NMR porosity gradually slowed down. When the centrifugal speed reached 12,000 r/min, the NMR porosity of the shale remained basically unchanged, which was close to the real bound-water state. Therefore, 12,000 r/min could be used as the boundary between movable fluid and bound fluid, and then the T\({}_{2}\) cutoff value of capillary movable water could be determined. At this time, the residual fluids corresponded to capillary-bound water and clay-bound water in small pores (Figure 8A). Figure 8B suggests that the NMR porosity of deep-marine shale could be divided into three parts based on drying temperature variation, and the porosity acquired through NMR at each stage changed obviously. The straight slope of the first part was large, the straight slope of the second part tended toward 0, and the straight slope of the third part was small. The different slopes indicate that different types of water in the shale were gradually evaporated. The first stage represented the main evaporation of movable fluid and capillary-bound fluid in the pores. When the temperature exceeded 80 \({}^{\circ}\)C, the movable fluid and capillary-bound fluid within pores were basically removed, but only when the temperature reached 120 \({}^{\circ}\)C could clay-bound water overcome resistance and migrate out of the shale pores. Therefore, the slope of the straight line in the second stage approached 0. When the drying temperature was below 200 \({}^{\circ}\)C, it was quite difficult to completely remove clay-bound water. When the temperature reached 200 \({}^{\circ}\)C, the bound water in clay could be effectively removed. However, this temperature could not remove the structural water in clay, so it would not devastate the pore structure of the clay. Stage 3 represented the evaporation of bound water in clay, resulting in a decrease in NMR porosity. Based on the above centrifugal and gradient-temperature-drying method, the NMR characteristics of shale samples could be classified into solid-related signals and fluid-related signals. The solid-related signals contained NMR signals of kerogen and dry clay. Fluid-related signals were composed of three parts: (1) clay-bound water, (2) capillary-bound water, and (3) movable water. After centrifugation at 12,000 r/min, the content of movable water could be acquired via T\({}_{2}\) spectrum (Figure 8). We believe that the signals in the shale mainly came from the fluid part, and compared to the signal contribution of the fluid, the signal contribution of the solid part of the shale could be ignored. After drying saturated water samples at 120 \({}^{\circ}\)C, these removed parts corresponded to movable water and capillary-bound water. The specific content could be calculated from the NMR data. When the drying temperature reached 200 \({}^{\circ}\)C, the removed part was clay-bound water, and its specific content was acquired through T\({}_{2}\) signals. The remaining part of the NMR response was a shale matrix signal with a smaller signal quantity (including  
Figure 8: NMR porosity changes in Wufeng–Longmaxi Formation deep-marine shale under different centrifugation and drying conditions. (**A**) NMR porosity variation curve with centrifugal speed; (**B**) NMR porosity variation curve with drying temperature. closed pores). Therefore, the shale NMR response mainly came from the fluid-related part at the T\({}_{2}\) time, representing the distribution range of the pore size. Fluids were further classified into four parts: (1) free, movable water; (2) capillary-bound water; (3) clay-bound water; and (4) closed-pore fluid (Figure 9). In a subsurface environment, the reservoir spaces of deep-marine shale filled by clay-bound water cannot be charged by shale gas.