# Quantitative Characterization of Micro-Scale Pore-Throat Heterogeneity in Tight Sandstone Reservoir
## 3 Discussions  
### Pore Throat Type and Physical Characteristics  
Based on the results of a cast thin section analysis of the Chang 6\({}_{3}\) reservoir, it is concluded that the main reservoir spaces are intergranular pores (3.81%), feldspar dissolution pores (0.65%), cuttings dissolution pores (0.23%), intercrystalline pores (0.12%), and micro-fractures (0.03%). According to the analysis of reservoir properties and pore throat capillary-pressure curve characteristics, the porosity distribution range of selected rock samples is 6.99% to 12.41%, the average value is 9.82%, the permeability distribution range is from 0.063 \(\times\) 10\({}^{-3}\) um\({}^{2}\) to 2.72 \(\times\) 10\({}^{-3}\) um\({}^{2}\), and the average value is 0.992 \(\times\) 10\({}^{-3}\) um\({}^{2}\). According to the standards of pore and throat size (Table 1), the selected rock samples represent three types of reservoir with different pore and throat combinations (macro pore-thin throat, macro pore-fine throat, macro pore-micro throat), as shown in Figure 1. The throat radius is greater than 1.0 um, and the storage space is mainly composed of intergranular and dissolved pores in a macro pore-thin throat reservoir with a permeability greater than 0.3 \(\times\) 10\({}^{-3}\) um\({}^{2}\). The throat radius is between 0.5 um and 1.0 um, and the storage space is mainly composed of dissolved pores, a few intergranular pores and micro pores in a macro pore-fine throat reservoir with a permeability between 0.1 \(\times\) 10\({}^{-3}\) um\({}^{2}\) and 0.3 \(\times\) 10\({}^{-3}\) um\({}^{2}\). The throat radius is between 0.1 um and 0.5 um, and the reservoir space is mainly composed of micro pores and a few dissolution holes in a macro pore-micro throat reservoir with a permeability of less than 0.1 \(\times\) 10\({}^{-3}\) um\({}^{2}\). Figure 1: Reservoir space and capillary-pressure curve characteristics of different reservoirs. (**a**) No.6, 1943.9 m, macro pore-thin throat, intergranular pores and dissolved pores are developed; (**b**) No.1, 2187.3 m, macro pore-fine throat, dissolved pores, a few intergranular pores and micro pores were developed; (**c**) No.3, 2148.79 m, macro pore-micro throat, micro pores and a few dissolved pores were developed. Quantitative Characterization of Pore Throat Micro-Scale Heterogeneity Based on Information Entropy Theory  
Based on the results of the constant velocity mercury-injection experiment and the information entropy theory, six representative rock samples with different types of pore-throat were selected to build quantitative models of microscale pore-throat heterogeneity, which allows to quantitatively characterize the micro-scale pore-throat heterogeneity of a tight sandstone reservoir. The results are shown in Tables 2 and 3. It can be seen from Table 2 that the Chang \(6_{3}\) reservoir in the study area generally developed macro pores, followed by meso pores, and little small pores. The uniformity of a macro pore-micro throat reservoir is between 0.7304 and 0.8224 and the average is 0.7722. The uniformity of a macro pore-fine throat reservoir is between 0.7249 and 0.7269 and the average is 0.7259. The uniformity of a macro pore-thin throat reservoir is 0.7324. Therefore, the distribution uniformity of pores in a macro pore-micro throat reservoir, macro pore-thin throat reservoir, and macro pore-fine throat reservoir becomes worse successively.