Oil migration in the Lunnan region, Tarim Basin, China based on the pyrrolic nitrogen compound distribution

Abstract

The distribution of pyrrolic nitrogen compounds (carbazoles and benzocarbazoles) in crude oils of the Lunnan region, produced from Ordovician, Carboniferous, Triassic and Jurassic reservoirs, are similar in the overall composition, but different in the total and the relative abundances of individual pyrrolic compounds. Since it was previously demonstrated that most of the Lunnan oils are sourced from the Middle–Upper Ordovician shaly carbonate rocks, and with similar maturity, these analytical results for pyrrolic nitrogen compounds indicate a remarkable geochromatographic fractionation effect during oil migration, especially for lateral secondary migration. Based on our results, we have shown that the migration and entrapment pathway of the Ordovician and Carboniferous oils is different from those for Triassic and Jurassic oils in the Lunnan region. That is, the Ordovician and Carboniferous oils migrated laterally from west to east, and their main filling points were on both southwest sides of the Lunnan and Sangtarmu Fault-horst Belts. On the other hand, Triassic and Jurassic oils migrated vertically via fault conduits from the Ordovician source kitchen and then migrated laterally from north to south.