Characterization of Crude Oil, Formation Water, and Fluid Inclusions of Hydrocarbon-Bearing Strata and Their Hydrocarbon Geological Significance in the Wuliyasitai Southern Sub-sag of the Erlian Basin, China

The hydrocarbon-bearing inclusions,formation water, and crudeoil contain a wealth of information regarding the process of accumulationof oil and gas. Their research has been one of the hotspots in thefield of oil and gas geology. Chemical analysis data was systematicallyemployed for the first time to identify the properties of liquid fluidsin the oil-bearing system of the Wuliyasitai southern sag in the ErlianBasin. A biased lacustrine algal input was shown by the stable carbonisotopes (& delta;C-13) of whole hydrocarbons, and the morphologicalcharacteristics of n-alkanes, isoprenoids, steranes,and terpenes were examined by gas chromatography-mass spectrometry.The & delta;C-13 values were determined by the salinity ofthe sedimentary water body and input of land-sourced materials. Thesignatures of the n-alkanes' molar fractionarrangement suggest that water washing, crystallization, and wax precipitationare regular occurrences in oil samples. The salinity of formationwater and the proportion of characteristic biomarkers (gammacerane,& beta;-carotene) demonstrate that the salinity of the ancient waterbody ranges from fresh water to brackish water. The correlation betweenthe stratigraphic water's characteristic coefficients and thetotal dissolved solids (TDS) is strong, particularly for the desulfurizationcoefficient, which illustrates a better hydrocarbon storage environmentwhen TDS is >6 g/L. The metamorphic coefficients demonstrate thatthe existing reservoir preservation circumstances are not optimal,and the TDS and concentration degree of formation water are positivelyconnected to the increasing depth, indicating poor longitudinal connectivity.The influence of atmospheric water infiltration is responsible forthe fluid inclusions' temperatures of homogenization (60 & DEG;C).However, due to deep burial, crude oil has not undergone secondarysignificant biodegradation despite the percolation of atmosphericwater. Besides, the distribution of reservoirs is highly correlatedwith formation water parameters such as the TDS, which can providescientific guidance for further exploration of oil and gas in thestudy area or even in the Erlian Basin.