原油稀有气体同位素特征及其示踪作用——以黄骅坳陷港西油田为例

以黄骅坳陷港西油田为例,测试并研究了原油中的稀有气体氦和氩同位素组成,并探讨了其示踪作用.研究表明:①港西油田6个未受空气污染原油样品具有幔源稀有气体介入的特征,其中氦气占介入稀有气体总量的139%～328%,平均为241%,说明港西油田具有幔源氦侵入的构造背景,且大地热流值较高,平均达750mWm^-2;②据原油⁴⁰Ar/³⁶Ar的年代积累效应,推测港西油田油源应为第三系烃源岩;③注水是港西油田原油稀有气体受空气污染的主要原因,对原油中的³He/⁴⁴²⁰⁴⁰Ar/³⁶Ar和⁴²⁰

Isotopic characteristics of noble gas in crude oil and their tracing significance

Taking Gangxi Oilfield in Huanghua Depression as an example,the isotopic compositions of noble gas in crude oil and their tracing significance were investigated.The ³He-to-⁴He ratios of six oil samples not contaminated by air indicated that those samples have contribution of mantle source.The percentage of the mantle-derived helium in the total contributed mantle source ranges from 13.9 percent to 32.8 percent, and the average value of six samples is 24.1 percent,which means that Gangxi Oilfield had the tectonic backgrounds for the input of the mantle derived helium and high geothermal flow value.The average geothermal flow value is 75.0 milliwatts per square meter.It is deduced from ⁴⁰Ar-to-³⁶Ar age accumulation effect that the Gangxi oil should be sourced from the Tertiary.Water injection resulted in the contamination of noble gas in the crude oil of Gangxi oilfield.The relations of ³He-to-⁴He ratio with ⁴He-to-²⁰Ne ratio and ⁴⁰Ar-to-³⁶Ar ratio with ⁴He-to-²⁰Ne ratio can be used to distinguish the water-injected wells and non-injected wells and to predict the effects of water injection.The application of research method for noble gas in crude oil to petroleum geology provides a new way for inferring natural gas and oil source,tectonic backgrounds，geothermal flow value and the effect of water injection in oilfield.