Total alkyl dibenzothiophenes content tracing the filling pathway of condensate reservoir in the Fushan Depression, South China Sea

Abstract

The condensates are generally characterized by high maturity, low concentration of steranes and terpanes biomarkers and low content of non-hydrocarbon fraction. In this case commonly used steranes, terpanes and carbazoles parameters cannot be effectively applied in the reservoir-filling tracing. The hydrogen bond formed by sulfur atom in the dibenzothiophenes (DBTs) results in molecule adsorption and fractionation during oil migration in reservoir. Like carbazoles, total DBTs content decreases with the increasing of oil migration distance. Therefore, a new parameter--total DBTs content is proposed to be used to trace the oil migration orientation and filling pathway. In present study, total DBTs contents of condensates and light oils are obtained by adding internal standard--eight deuterium atoms substituted DBT during Gas Chromatography-Mass Spectrometry analysis of aromatic fraction. Except for a few samples with much lower content of non-hydrocarbon fraction, the total DBTs content shows a fine positive correlation with that of carbazoles. Large errors can be caused in the process of pyrrolic nitrogen compounds separation. The application of this new parameter in the Fushan Depression of Beibu Gulf Basin, South China Sea indicates that this parameter is a reliable one to trace filling pathway in condensate reservoirs. Combined with other DBTs-related parameters, such as 4-/1-methydibenzothiophene and 2,4-/1,4-dimethyldibenzothiophene, oil migration orientation and filling pathway of the Fushan Depression was determined. The accumulations of Huachang oil field in the Fushan Depression are mainly migrated and charged from northeast to southeast along the Huachang uplift. It can be predicated that the light oil and condensates in the Huachang oil field should be sourced from the source kitchen at the Bailian Sag. It shows that total DBTs content is an effective parameter to tracing oil migration orientation and filling pathway. dibenzothiophene, alkyl dibenzothiophene, condensate reservoir, filling pathway, molecular markers, the Fushan Depression England et al. [1,2] first established a filling model of petroleum in sandstone reservoir, providing a scientific theory basis for reconstruction of oil migration pathways and orientation, definition of filling point and potential source kitchen as well as predication of "satellite reservoir" based on the differences of oil maturity, the oil/gas ratio, oil physical properties, etc. Since then, the focus of the petroleum geochemists has moved from exploration and increasingly towards production and reservoirrelated problems.Reservoir geochemistry has been developed and successfully applied in the petroleum exploration, reservoir appraisal and production monitoring [2] , but some limitations have been met in condensate and light oil reser-

Geochemistry and origin of Ordovician oils in the Rewapu Block of the Halahatang Oilfield (NW China)

“…(e) (f) As demonstrated by previous studies, the relative abundances of methylated DBT isomers and the absolute concentrations in oils are also relative to migration distance. Therefore, the ratios of methylated DBT isomers and concentrations of total DBTs for oils derived from same source bed/kitchen can be applied to trace oil migration direction and charging pathway (Wang et al 2004;Li et al 2008Li et al , 2014aFang et al 2016Fang et al , 2017a. Except for one case study in a Tertiary sandstone reservoir in the Beibuwan Basin, South China Sea, we also found that the absolute concentration of DBTs was not an effective indicator for tracing oil migration orientation in Tarim Paleozoic carbonate reservoirs (Li et al, unpublished data).…”

Oil charging history and pathways of the Ordovician carbonate reservoir in the Tuoputai region, Tarim Basin, NW China

“…These molecular indicators were successfully applied in Tertiary sandstone reservoirs in the north margin basins of the South China Sea (Wang et al 2004a;Li et al 2008) and in the Ordovician carbonate reservoir of a karst pore-fissurenetwork type in the Tahe and Halahatang Oilfields of the Tarim Basin (Wang et al 2004aLi et al 2014a, b;Fang et al 2016). The results suggest that these parameters can be used as an effective tracing indicator for oil filling orientation and migration pathways.…”

Migration and accumulation of crude oil in Upper Triassic tight sand reservoirs on the southwest margin of Ordos Basin, Central China: A case study of the Honghe Oilfield

“…But the other three are applicable over a wide range of maturity and correlate well with each other; therefore, this paper chose Ts/ (Ts + Tm) and C 29 Ts/C 29 H as representative for the next study ( Figure 7). Previous studies (Fang et al, 2016;Li et al, 2008;Wang, He, Li, Hou, & Guo, 2004) have demonstrated that the parameters of alkyl dibenzothiophene (dibenzothiphenes, methyldibenzothiphenes…”