## 1 Introduction  
By 2020, the global oil production was about 4 billion tons per year, and about 8 million tons of crude oil entered the soil-water environment as a pollutant every year. Coastal oil pollution is an important part of soil-water pollution. Oil pollution resulted in reduced coastal vegetation and coastal organisms, increased erosion of swamp marginal habitats, disrupted nutrient cycling and water filtration, and the other regulatory functions of swamps, causing serious damage to coastal ecosystems [1]. As a typical non-aqueous phase liquid (NAPL), leaked oil has a complex composition, low solubility in water, strong binding ability with soil organic matter, strong anti-desorption ability and is difficult to remove from the soil aquifer [2]. After entering the soil, it blocks the pore structure of soil particles, changes the soil physical properties such as soil texture, compaction degree, structure state and the concentration and content of soil minerals and heavy metals, which seriously affect the functions of soil and the underground ecological environment [3]. Many hydrocarbon pollutants, especially polycyclic aromatic hydrocarbons (PAHs), also inhibit plant growth, damage the diversity and integrity of the soil microbial community, and disrupt or even destroy the regular soil micro-ecological environment. Direct or indirect contact with organisms may cause serious harm to biological health. Nowadays, petroleum-contaminated soil remediation technologies can be divided into three categories, according to the different disciplines involved: physical; chemical; and biological remediation technologies. However, the treatment process of physical and chemical remediation technology is complex, and the cost is high. It is easy to produce secondary pollution, and cannot fundamentally remove pollutants. It is usually only suitable for repairing small areas and high concentrations of petroleum-contaminated soil. For the remediation of large-scale and low-concentration petroleum-contaminated soil, compared with various physical and chemical decontamination methods, bioremediation technology has the advantages of high efficiency, economy and environmental protection [4]. Bacterial chemotaxis refers to a microbial characteristic of bacteria [5; 6], which can respond to the gradient of chemical concentration in water and migrate to areas conducive to its survival and growth. Many studies showed that bacteria have chemotaxis to many petroleum hydrocarbon pollutants [7]. Researchers observed the chemotaxis migration (chemotaxis) of chemotactic bacteria to the contaminated layer by designing heterogeneous sand columns or sand boxes [8; 9; 10; 11], but the black box effect reduced the repeatability of the experiment, bringing great difficulties to the quantitative results. [PERSON] et al. carried out innovative research on mesoscopic scale (Darcy scale), which laid the foundation for visualization of chemotactic bacteria on mesoscopic scale [12; 13]; some experiments used microfluidic chips to study the remediation of non-aqueous pollution in heterogeneous soil at the micro-scale [14; 15; 16; 17]. Other experiments showed that exercise-type bacteria had chemotaxis towards petroleum hydrocarbon pollutants that they could degrade. Most bacteria have sensory systems that can help them detect and respond to petroleum hydrocarbon pollutants. The chemotaxis of bacteria and their ability to degrade petroleum hydrocarbons enable them to contact directly with soil pollutants, thereby accelerating the degradation of petroleum hydrocarbons in these areas. Many of the microbes living in oil reservoirs consume hydrocarbons. In order to do this, they must break down the long alkyl chains that are present in heavy crude oil. By degrading these chains, bacteria increase the amount of valuable, light crude [18]. Some microbial oil displacement bacteria also have chemotaxis [19], so studying and understanding bacterial chemotaxis has a strong practical significance for oil pollution remediation and enhanced oil recovery (EOR) [20].