Study on Oil Migration in Hashan Region of Junggar Basin Based on the Distribution of Pyrrolic Nitrogen Compounds

Abstract

In order to determine oil migration direction and pathway in Hashan region, Junggar basin, China, pyrrolic nitrogen compounds have been chose as trace markers of oil migration. In this study residual oil in the core samples (Permian-Cretaceous), from eight wells in Hashan region, was investigated. Firstly, the samples were separated using column chromatography and saturated hydrocarbons, aromatics and pyrrolic nitrogen compounds were obtained. Secondly, All the three fractions were analyzed by gas chromatography-mass spectrometry (GC-MS) and comprehensive two-dimensional gas chromatography coupled to a time-of-flight mass spectrometry (GC×GC-TOFMS), respectively. Several geochemical parameters on biomarkers were calculated and diagrams of oil-oil and oil-source correlation were achieved. Based on the results, all samples were proved to be of similar sedimentary environment (reductive environment), source (terrestrial plant) and maturity (low maturity), and the oil samples were generated from a source rock of Fengcheng formation. It also indicates that the difference of distribution of pyrrolic nitrogen compounds is mainly caused by oil migration. In addition, the chromatograms from GC-MS and GC×GC-TOFMS were compared in detail and GC×GC-TOFMS showed higher resolution for target analytes, which is beneficial to the quantification of compounds and study of oil migration. According to the results, seven dimethylcarbazole ratios (shielded/semi-shielded, shielded/exposed) and one benzocarbazole ratio were calculated. Based on the results, the data points were plotted in well location map and structural profile map. It shows that the lateral distributions of carbazole isomers are not obvious. The possible reason is that the distances among the wells are very short (less than 800 meters). By contrast, the vertical distributions of carbazole isomers are obvious. The ratios of 1,8-/2,7-dimethylcarbazole, 1,8-/1,6-dimethylcarbazole and 1,8-/1,7-dimethylcarbazole etc. increased with the decreasing depth except for carboniferous samples. Furthermore, the ratio of benzocarbazole [a]/([a]+[c]) is irregular, and so cannot be applied in Hashan region. Combined the experimental results with the regional geological data, the migration direction and pathway of oils in Hashan region is determined, and a conclusion is drawn that the carboniferous oils in thrust nappe didn't migrate from the deep of Mahu sag, but from source rocks of northern deep Fengcheng formation.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015