## 1 Introduction  
In 2020, the total geological resources of dense sandstone gas in China reached 2.09 trillion cubic meters, becoming the most unconventional natural gas type with the highest proven rate, accounting for 30.9% [1]. It is expected that in the next 5 to 10 years, China's dense sand rock gas industry will enter a period of rapid development. From the perspective of technology recoverable reserves, proven reserves and output, etc., the dense sand rock gas is undoubtedly the most realistic and priority mining value in China. The type of natural gas is unconventional [2, 3].  
Because the density sandstone gas collection matrix storage layer has the characteristics of pore structure with small pore throat and high hairy power, fracture technology is a strategy that effectively improves the harvest. The invasion of the liquid invasion caused the clay absorption of the clay without compatibility with the reservoir, which increased the clicks of the clay binding water, causing clay to expand, decentralized, and transported. The spacious pores of the fluid infiltration were reduced, and the infiltration channel was blocked. In the end, the heart penetration rate of the rock was reduced, and the storage layer was given to the storage layer. Bring serious damage [4, 5].  
Domestic scholars have done many research work for hydrophilic damage [6, 7, 8, 9]. In order to maintain the permeability of the oil and gas layer, prevent the reservoir from being damaged, and ensure the stable and high yield of the oil and gas fields, the efficient oilfield chemical treatment agent of clay stabilizers has been widely used. Compared with the traditional cationic surfactant, double-season ammonium salt has shown excellent performance due to its unique double-season ammonium positive ion adsorption center [10]. It has excellent water solution, high surface activity and low surface tension, and its CMCvalues are relatively low. Based on this, the water sensitivity damage of dense sandstone storage layer has been prepared, and the quality of low relative molecularity is prepared (less than 1000). Double-season ammonium salt clay stabilizers replaced the original clay stabilizer to prepare new fissure [11; 12]. We mainly evaluate the basic performance of the fracture fluid for different fracturing liquids, and less micro-pores before and after the damage [13; 14; 15]. At the same time, with the increase of the feed pressure, the throat and large pores of the rock heart are compressed to deform, and some ultra-fine small pores are even closed [16]. In particular, the dense reservoir is affected by factors such as strong non-average quality, small pore throat, and factors. Its corresponding stress sensitivity is relatively strong, which will cause the fracture to change the damage to pore structure [17; 18; 19].  
Nuclear magnetic resonance is a kind of non-destructive testing technology that can test the pore structure of the rock body without destroying the pore structure of the rock body, which is close to the \"original\" test status. In additionRepeatability [20]. [PERSON] et al. conducted gas-driven water experiments for various types of sandstone samples, and in-depth research on the form of water in the rock pores combined with nuclear magnetic resonance technology. [PERSON] et al. [21]. adopted MRI's resonance imaging technology and T2 spectrum analysis methods to deeply discuss the pore classification of sandstone and the uniformity of the pore diameter distribution during the driving process.  
This article uses the low-field nuclear magnetic resonance system equipment to conduct pore characteristics of the dense sandstone reservoir. Analyze the changes in different scale pores of the reservoir damage when the siege effect of the siege is performed.