Characteristics of newly discovered crude oil in the Weihe Basin and its petroleum geological significance

Li Yuhong; Gao Gang; Wang Xingyun; Qu Tong; Han Wei; Gong Zhenqi; Zhang Wen; Dang Wenlong

doi:10.11743/ogg20190213

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Characteristics of newly discovered crude oil in the Weihe Basin and its petroleum geological significance
Vol. 40, Issue 2, Pages: 346-353(2019)
Online First：28 April 2019，

Published：2019
DOI： 10.11743/ogg20190213
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DOI：

Li Yuhong, Gao Gang, Wang Xingyun, et al. Characteristics of newly discovered crude oil in the Weihe Basin and its petroleum geological significance[J]. 2019, 40(2): 346-353. DOI： 10.11743/ogg20190213.

摘要

渭河盆地地热井中意外发现有石油产出，打破了该盆地无油的历史定论。为了认识该原油的特征及其油气地质意义，对采集的地热井原油的物性、族组分含量、饱和烃含量、甾烷与萜烷组成、饱和烃单体烃碳同位素组成进行了系统分析。分析表明，原油以饱和烃为主、芳香烃和沥青质次之，胶质含量最低，属于正常含蜡、低硫、轻胶质原油。饱和烃色谱呈双峰型，主峰为C

和C

，CPI和OEP值分别为0.93和0.90。原油母质成熟度较高且主要来自浮游水生生物和少量高等植物，并有藻类有机质的贡献。正构烷烃中低碳数（C

-C

）的碳同位素值随碳数增加而从-27.1‰降低到-30.3‰；当碳数高于C

后，碳同位素值在-29.3‰和-30.4‰之间变化；姥鲛烷（Pr）和植烷（Ph）的碳同位素值重，分别为-26.1‰和-24.9‰。相对较高的伽马蜡烷含量表明了原油母质形成于较高盐度的水体中。通过邻区对比发现，该原油特征与鄂尔多斯盆地二叠系、三叠系延长组、侏罗系等已知产油层位的原油差别较大，显示出明显的地球化学与成因的特殊性。新发现原油表明渭河盆地应具有尚未发现的生烃源岩，对渭河盆地的油气勘探具有重要的指导意义，同时也可为鄂尔多斯周缘盆地新层系油气调查提供借鉴。

Abstract

The unexpected production of oil from the geothermal wells in the Weihe Basin breaks the conclusion of history that there is no oil distributed in the region.We made a systematic study of the crude oil in terms of its physical property

group composition

content of saturated hydrocarbon

composition of sterane and terpane

as well as carbon isotope composition of saturated hydrocarbon monomer

with a view to explore the characteristics of crude oil and its petroleum geolo-gical significance for the basin.The results show that the crude oil compositions are predominated by saturated hydrocarbons

followed by arene and asphaltene

and with the colloid coming last

thus it belongs to a kind of low-sulfur crude oil with light colloid and normal content of wax.Its saturated hydrocarbon chromatogram is bimodal

with the main peaks corresponding to C

and C

and the CPI and OEP values are 0.93 and 0.90 respectively.The organic matters of the crude oil are high in maturity

and mainly sourced from planktons

followed by certain higher plants and algaes.The carbon isotope value of low n-alkanes (C

-C

) decreases from -27.1‰ to -30.3‰ along with the increase of carbon number.When the carbon number is higher than C

the carbon isotope value varies between -29.3‰ and -30.4 ‰.In addition

the carbon isotope values of pristane (Pr) and phytane (Ph) are relatively heavy at 26.1‰ and 24.9‰

respectively.Higher content of gammacerane indicates that the organic matters are produced in an environment of higher salinity.Compared with the adjacent areas

the crude oil has a great difference with that from the Permian

the Triassic Yanchang Formation and the Jurassic in the Ordos Basin in terms of geochemistry and origin.The newly discovered crude oil indicates that the Weihe Basin may still have source rocks undiscovered

which is of great significance to guide the petroleum exploration of the basin.At the same time

it is also of referential meaning for oil and gas survey in the unexplored sequences in Ordos Basin.