Geochemical evidence for the origin of multiphase hydrocarbons in the deep carbonate platform margin: examples of Ordovician oil in the Yuke of the Tarim basin

Abstract

The genetic mechanism of high-maturity light oil reservoirs has long been an issue in deep oil and gas exploration. In order to better examine the development of multiphase hydrocarbon reservoirs on the edge of the Ordovician carbonate platform in the Yuke Tarim Basin, this research used the application of organic geochemistry techniques. An analysis of the light hydrocarbon components and triarylsterane parameters of the Ordovician oil confirmed that the oil was produced from the mature to highly mature stage and was sourced primarily from the lower Cambrian Yuertusi Formation. A significant discovery from this investigation is the gradual increase in aromatic parameters of crude oil, including methyl dibenzothiophene (4-MDBT/1-MDBT) and the trimethylnaphthalene index (TMNr), indicating two fluid migration routes—vertical and lateral—for hydrocarbons within the carbonate platform margin. These findings provide a new insight into the underlying mechanism of deep multistage differential hydrocarbon accumulation. The discontinuous distribution of gypsum and salt rocks and the activity of strike-slip faults control the intensity of late-stage natural gas intrusion, which is a key factor in the formation of multi-phase oil and gas enrichment.The discontinuous presence of the middle Cambrian gypsum cap at the base of the study site resulted in a notable increase in late gas invasion. The vertical strike-slip fault zone and transverse transport system play crucial roles in the spatial distribution of hydrocarbons at the carbonate platform margin. Additionally, the analysis underscores the significant value of aromatic parameters of crude oil in identifying the genetic characteristics of highly mature oil and gas.