Molecular composition of asphaltene in wellbore blockage on the southern margin of Junggar Basin

Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) was employed to analyze the compositional differences of asphaltene of oil and blockage extracts of well Gaotan 1 on the southern margin of Junggar Basin. The correlation between asphaltene composition and structure and precipitation was discussed, which is important for the research of asphaltene precipitation and accumulation. Results showed that the asphaltene molecules of oil and blockage extracts of well Gaotan 1 are mainly composed of N1, N1O1, O1, O2, O3 and O4 class species. However, the degree of asphaltene condensation in blockage extract is significantly higher than that in oil, and it is enriched with O2, O3 and O4 class species. It indicates that during the flow of formation crude oil in wellbore, the precipitation of asphaltenes with different compositions has a certain selectivity. Asphaltene components with high condensation degree preferentially precipitate and deposit, forming a solid core. Among them, polyoxo-heteroatom compounds have relative strong polarity, which accelerates the precipitation of other asphaltene components in crude oil to form blockage. Asphaltene in blockage extract has a complex molecular structure and a wide range of condensation degree. The DBE values distribute between 9 and 30. Its molecular polar force parameter is larger and the distribution range is wider. Therefore, it is ideal to select a mixed solvent similar to the polar force parameter of blockage asphaltene to remove blockage.