Aiming at the wellbore plugging problem of two production wells in an oilfield in Xinjiang, the composition and formation mechanism of the plugging materials were systematically investigated by means of component analysis, stability evaluation, hot-stage microscopy, and property comparison experiments. The results show that the dominant factors for plugging in the two wells are significantly different. For Well #1, the plugging material is dominated by inorganic solid phase, with cuttings (toluene-insoluble matter) accounting for 86.21 wt%, indicating a cuttings-dominated inorganic plugging. For Well #2, the plugging material is dominated by organic heavy components, with oil sample (toluene-soluble matter) accounting for 95.72 wt%, in which the asphaltene content is as high as 58.42 wt%, far exceeding that in the crude oil (1.09 wt%), indicating an asphaltene aggregation-dominated organic plugging. The colloidal stability parameter based on SARA fractions shows that the crude oil from Well #2 has a poor stability with a parameter of 2.89, indicating a significant risk of asphaltene precipitation. Hot-stage microscopy observations indicate that, under atmospheric pressure and within the temperature range of 30?°C to 120?°C, temperature has a reversible effect on the asphaltene aggregation behavior of Well #2 crude oil: heating promotes asphaltene dispersion, with the number and size of particles decreasing; cooling accelerates asphaltene precipitation and aggregation, with the number of particles increasing significantly, and small particles with a particle size less than 5?μm are the most sensitive to temperature changes. Compared with asphaltenes in the crude oil, asphaltenes in the plugging material show obvious enrichment characteristics: the aromatic carbon fraction (fA) increases from 0.46 to 0.65, the average molecular weight increases from 2849 g·mol-1 to 3862 g·mol-1, and the number of structural units increase significantly, which is the key internal cause for organic plugging. Furthermore, cuttings can significantly accelerate the particle size growth of aggregates by adsorbing asphaltenes. The settling velocity of asphaltene combined with cuttings is about 219 times that of pure asphaltene particles, aggravating the plugging risk. This study clarifies the core causes and key influencing factors of wellbore plugging in the two wells, providing a theoretical basis for the optimization of anti-blocking and deblocking processes for similar types of oil wells.