Abstract
Recent exploration work in the Tazhong district has gradually transferred to the exploitation of high and over mature oils in deep and ultra-deep layers. This has proved problematic, however, as the distribution of crude oils in the Tazhong is complex. This means that the geochemical characterization of high and over mature oils, especially for light crude oils, have become increasingly important. The stability of concerted ring structure of aromatics makes them having stronger thermal stability and resistance to biodegradation. This means that there are abundant aromatic compounds in high and over mature oils. This study presents a series of geochemical analyses of the maturity parameters of 89 crude oils from the Tazhong area, including stable carbon and hydrogen isotope analyses of compounds from 43 light crude oils. These analyses are then compared with other data from the Tazhong Number I fault zone, as well as the Tazhong Number 10 and Tazhong Uplift structural zones. Results show that the geochemical parameters of oils from Tazhong Number I fault zone generally encompass a wider range than those from the Tazhong Number 10 structural zone, which indicates that the Tazhong Number I slope belt is more active than its counterpart structural belt and generates oils with more complex geochemical characteristics. The positive correlation between the toluene/methyl cyclohexane ratio and the dibenzothiophene/phenanthrene ratio, as well as with the naphthalene/phenanthrene ratio indicates that aromatization parameters can be used to evaluate the maturity of light crude oils, and there may be inherited relationships between toluene and methyl cyclohexane in crude oils.
Highlights
The Tarim Basin has experienced a number of structural movements, which has led to a series of complex and diverse structural styles, and large differences in oil characteristics between different zones
The fact that large volumes of light crude oil have been extracted from the Tazhong (TZ) area within the Tarim Basin highlights the great potential for massive petroleum exploration from deep layers in this region (He et al, 2016; Wang et al, 2014)
A total ion chromatogram (TIC) and the compounds identified in selected TZ black oil samples are presented in Figure 2; within these samples, TZ26, TZ44 and TZ241 are located within the TZ Number I fault zone, while TZ4, TZ104 and TZ404 are located within TZ Number 10 structural zone, and TZ12, TZ35 and TZ162 are located within the central uplift zone
Summary
The Tarim Basin has experienced a number of structural movements, which has led to a series of complex and diverse structural styles, and large differences in oil characteristics between different zones. The fact that large volumes of light crude oil have been extracted from the Tazhong (TZ) area within the Tarim Basin highlights the great potential for massive petroleum exploration from deep layers in this region (He et al, 2016; Wang et al, 2014). Because of the high maturity of light crude oils, a number of normal geochemical evaluation parameters cannot be applied. Several structural movements have changed, or even destroyed, crude oils within the Tarim Basin to different degrees; the geothermal changes induced by these movements have affected the thermal evolution of hydrocarbon source rocks and caused large differences in the maturity of crude oils at different phases
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