The Application of Nitrogen Compounds to Indicate Oil Migration on the Biodegraded Oils: A Case Study From Hashan Region, Junggar Basin

Abstract

Hashan region is located in the northwest of Junggar Basin, China. Oil and gas resources and oil migration are not clear in this area. In order to determine oil migration direction and pathway in Hashan region, pyrrolic nitrogen compounds were firstly applied to the biodegraded oils for indicating oil migration. In this study thirteen core samples (Permian-Cretaceous) from eight wells in Hashan region were investigated. Firstly, the samples were separated by column chromatography, then 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 the biodegradation levels of the samples were confirmed. In addition, 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 the same source rock. Thus, the variance in the distribution of pyrrolic nitrogen compounds among the oils most likely resulted from migration-related fractionation. In addition, the chromatograms of GC×GC-TOFMS showed higher resolution for the target analytes than GC-MS, which benefits to the qualitative and quantitative research of the nitrogen compounds. Seven dimethylcarbazole ratios and one benzocarbazole ratio were calculated. The dimethylcarbazole ratios, as well as the dimethyl-dibenzothiophene ratios, increased with the decreasing depth which showed that the vertical direction of oil migration is from deep to shallow. Furthermore, the distributions of homogenization temperature of fluid inclusions in reservoir rocks indicated two stages of oil migration and accumulation in Hashan region. Combined the experimental results with the regional geological data, conclusions have been drawn that the oils of the thrust nappe in Hashan region didn't migrate from Mahu sag, but from Fengcheng source rock beneath the nappe and the potential oil migration pathway were faults and associated fractures. At last, we determined that the method of using nitrogen compounds to indicate oil migration can apply to the biodegraded oils which biodegradation level doesn't exceed 5.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015