Geochemical characteristics and origin of oil and gas in No.2 structural belt of Nanpu sag in Bohai bay basin
The No.2 structural belt in the Nanpu sag of Bohai bay basin has the characteristics of multi-sag and multi-layer hydrocarbon supply.In order to reveal its complex oil and gas sources,geochemical tests such as chromatography-mass spectrometry are conducted to analyze the geochemical characteristics of crude oil.The crude oil is categorized into three types and the specific sources of each type are identified.The results show that:①Type Ⅰ crude oil is mainly distributed in the third member of the Eocene Shahejie Formation(Es3)reservoir of the western structural belt.The relative content of C27 and C29 regular steranes in the crude oil are similar,and the pregnane parameters((pregnane+homopregnane)/regular sterane)and sterane isomerization parameters(C29 sterane 20S/(20R+20S),C29 steraneββ/(αα+ββ))are relatively high,indicating a combined input from aquatic organisms and higher plants.The crude oil demonstrates high maturity and is derived from the source rock of Es3.②Type Ⅱ crude oil is primary distributed in the second member of the Eocene Dongying Formation(Ed2)reservoir of the western tectonic belt.It is characterized by a noticeable predominance of C29 regular steranes,coupled with lower pregnane parameters and sterane isomerization parameters.The crude oil's source material is notably dominated by higher plants.This crude oil exhibits lower maturity and originates from the source rocks of Es1-Ed3.③Type Ⅲ crude oil is predominantly distributed in the Ed3 reservoirs of the eastern tectonic belt and the Ed1 and Minghuazhen Formation of the western tectonic belt.There is a certain advantage in the C29 regular sterane content,with lower pregnane parameter and higher sterane isomerization parameter.The crude oil is dominated by higher plant input and with higher maturity,and be identified as a composite source originating from three sets of hydrocarbon source rocks.④The 4-/1-MDBT and Ts/Tm indices of the crude oil show a decreasing trend towards the shallow strata along the fault.Notably,the vitrinite reflectance values converted from the methylphenanthrene in the crude oil are consistent with the vitrinite reflectance in the underlying source rock,indicating that the crude oil in the study area is characterized by in-situ hydrocarbon supply.The findings in the study can provide theoretical guidance for both detailed exploration in the shallow strata and deep exploration in the area.
Bohai bay basinNanpu sagNo.2 structural belttype of crude oilgeochemical characteristicsbiomarkeroil-source rock correlationinn-situ hydrocarbon supply
万方数据
维普
