## 1 Introduction  
According to statistics, more than 60% of the world's oil reserves are located in carbonate reservoirs, many of which are enriched in natural fractures, and the mechanism of oil and gas recovery in natural fracture-type reservoirs is more complicated than that in conventional reservoirs [1]. However, since more than 20% of the world's oil is extracted from naturally fractured reservoirs, the study of the recovery rate of naturally fractured reservoirs has always been a direction of attention [1; 2; 3; 4; 5; 6; 7; 8]. Natural fracture-type reservoirs refer to oil and gas reservoirs in which the storage space and percolation channels of the reservoir are mainly fractures [4; 5]. Reservoirs are generally dense and brittle rock formations with non-permeable and poor permeability, and the lithology is highly heterogeneous. The causes of fractures are diverse, but tectonic fractures are predominant, so fractured oil and gas reservoirs are classified into the broad category of tectonic reservoirs, and if the reservoir tectonic map is backslope, it can also be called fractured backslope oil and gas reservoirs. Compared with other types of oil and gas reservoirs, fracture-type oil and gas reservoirs have some significant features. For example, the original porosity of reservoirs in fracture-type reservoirs varies, and the permeability is extremely low, but the permeability is very high in the fracture development zone. In addition, the distribution of pore permeability development in fracture-type reservoirs is extremely uneven, and the oil and gas storage performance varies greatly in different parts of the same reservoir. The core permeability of oil and gas reservoirs measured in the laboratory is often very low, but in the subsurface, due to the development of fractures, communicating the various storage spaces in the reservoir, forming an unimpeded seepage system, the actual permeability of the reservoir in the extraction is very high [7; 8; 9; 10; 11]. As a type of fractured reservoir, one of the challenges in hydrocarbon recovery from carbonate reservoirs lies in the wettability characteristics of the reservoir rock. Statistically, it has been observed that up to 77% of carbonate rocks exhibit non-water-wet behavior, indicating that water injected into the fractures and pores does not readily flow [5; 6]. Additionally, the permeability in fractured reservoirs is typically significantly greater than that in rock pores, rendering viscous forces relatively insignificant. Consequently, conventional waterflooding techniques for enhanced oil recovery often prove ineffective in propelling surfactants into rock pores, which serve as the primary zones of hydrocarbon accumulation in fractured reservoirs due to their superior retention capabilities compared to fractures. While employing high-temperature and high-pressure gas injection techniques can enhance recovery rates in such reservoirs, this approach invariably incurs elevated costs [10; 11; 12; 13; 14; 15; 16; 17; 18]. In oil-wet and mixed-wet fractured reservoirs, the conventional secondary recovery strategy of enhancing hydrocarbon recovery via water injection often fails to achieve significant results. This is primarily due to the presence of capillary forces which inhibit the ingress of water into rock pores, thereby impeding the displacement of hydrocarbons. Consequently, it becomes imperative to decrease the interfacial tension (IFT) and modify the contact angle in order to improve recovery efficiencies in these types of reservoirs. In practical application, interfacial tension is generally reduced by adding surfactants to the injection water [15; 16; 17]. Furthermore, surfactants are capable of altering the wettability of carbonate rocks to enhance their hydrophilicity. Different classes of surfactants, including cationic, nonionic, and anionic, employ distinct mechanisms to modify wettability. Among these, cationic surfactants are particularly effective in significantly influencing the wettability properties of the rock surfaces.