Geochemistry Of Polycyclic Aromatic Hydrocarbons And Nonhydrocarbons: Tracing Markers For Oil Filling Orientations And Pathways

Dibenzothiophenes(DBTs)and benzo[b]naphthothiophenes(BNTs)are the main sulfur-containing heterocyclic aromatic compounds in crude oils and sedimentary rock extracts.Because of the relatively higher electronegativity and an unshared pair of electrons in the outer shell orbital of the sulfur atom,hydrogen bonds can be formed between the sulfur and hydrogen atoms of the circumferential medium in carrier beds.Therefore,DBTs and BNTs are potential geochemical markers for tracing oil filling pathways.Halahatang Depression is located in the center of the Tabei Uplift of Tarim Basin,Northwest China,and is one of the most commercially prolific petroleum regions of the Tabei Uplift.Based on the analyses of the molecular marker of the typical oil sets,we can do oil-oil correlation,classify oil family/ population and relate the oil charging timing and eposides trace the oil filling orientation and pathways.In this study,we collect 80 oil samples of 78 drilling wells from the Halahatang Depression.The correlation of all oils in the Halahatang Oilfield of the Tabei Uplift in the Tarim Basin(NW China)shows that the molecular marker compositions of all oils are quite similar,implying that these oils have been sourced from the same source kitchen/bed and belong to a same oil family.Combined the measured homogenization temperatures(Th)of the aquatic inclusions in the reservoir rocks with the burial and geothermal histories reconstructed using One-D basin modeling,we can relate the Th to the relevant geological ages.We concluded that the Halahatang Depression has charged twice,the first charging history was from 420-410 Ma and the second 20-6 Ma,corresponding to the Middle to Late Silurian and the Pliocene,respectively.Using molecular indicators relative to DBTs and BNTs compounds,namely,4-/1-MDBT(4-/1-methyldibenzothiophene),4,6-/(1,4 + 1,6)-DMDBT(4,6-/(1,4 + 1,6)-dimethyldibenzothiophene),(2,6 + 3,6)-/(1,4 + 1,6)-DMDBT((2,6 + 3,6)-/(1,4 + 1,6)-dimethyldibenzothiophene),2,4,6-/(1,4,6+1,4,8+3,4,6)-trimethyldibenzothiophene,(2,4,7+2,4,8)-/(1,4,6+1,4,8+3,4,6)-trimethyldibenzothiophene and [2,1]BNT/([2,1]BNT + [1,2]BNT)(benzo[b]naphtho[2,1-d]thiophene /(benzo[b]naphtho[2,1-d]thiophene + benzo[b]naphtho[1,2-d]thiophene)),this paper traces the oil migration orientation and filling pathways in this oilfield.The isopleth maps of the aforesaid molecular indicators unequivocally reveal an overall oil migration,filling points,and preferred filling pathways orientation from south to north.Based on this,a potential source kitchen is predicted in the southern part of the Halahatang Depression,most probably at the Manxi(Shuntuoguole)Low Uplift,just between the Awati and Manjiaer depressions.The southern part of the Halahatang Depression,along the oil charging pathways,is predicted to be the most promising region for oil exploration.