柴达木盆地北缘天然气成因类型及气源判识

测试并分析了柴达木盆地北缘9个油气田(圈闭构造)第三系和白垩系35个天然气样品的组分和碳同位素组成,建立了柴北缘天然气成因类型的判识指标,划分其热演化阶段,并进行了气源判识。研究结果表明:1)柴北缘天然气可划分为煤型气、油型气和混合气3种成因类型。伊克雅乌汝、南八仙、冷湖五号、鄂博梁以及马北的部分样品具有煤型气特征;冷湖三号、冷湖四号及冷湖五号和马北个别样品具有油型气特征;葫芦山和马北部分样品属于混合气。2)伊克雅乌汝、南八仙、冷湖五号和鄂博梁等煤型气样品大多数处于高成熟演化阶段;冷湖三号和冷湖四号部分油型气样品的成熟度较煤型气的偏低,大多数处于成熟演化阶段;葫芦山的天然气为接近过成熟阶段的高熟气;马北天然气样品的成熟度变化范围较大。3)冷湖三号、冷湖四号、冷湖五号、鄂博梁、葫芦山的天然气主要来自于昆特依凹陷,其中冷湖三号的天然气应源于昆特依凹陷偏腐泥型母质,而冷湖四号、冷湖五号、鄂博梁、葫芦山的天然气应源于昆特依凹陷偏腐殖型母质;南八仙的天然气主要来自于下侏罗统(J1)伊北凹陷偏腐殖型母质;马北的天然气来源比较复杂,可能来自于伊北、赛什腾、尕西等多个生烃凹陷。

A study on genetic types and source discrimination of natural gas in the north margin of the Qaidam Basin

Based on the analyses of chemical components and carbon isotopic composition of 35 natural gas samples from the Tertiary and Cretaceous reservoirs in 9 fields or trap structures in the northern edge of Qaidam Basin,we defined indexes for identifing genetic types of gas,determined the thermal evolutionary stages,and identified the sources of natural gases.The result shows that the natural gases in the north margin of Qaidam Basin can be divided into three genetic types:coal-type,oil-type,and hybrid-type.Some of the gas samples from Yikeyawuru,Nanbaxian,Lenghu-5,Eboliang and Mabei are of coal-type gas;several gas samples from Mabei and Lenghu-3,Lenghu-4 and Lenghu-5 are of oil-type,and some gas samples from Hulushan and Mabei are of hybrid-type.Samples of coal-type from Yikeyawuru,Nanbaxian,Lenghu-5,and Eboliang,are mostly at high maturation stage;those of oil-type from Lenghu-3 and Lenghu-4 are mostly at maturation stage,those from Hulushan are at over-mature stage,while samples from Mabei have highly-varying maturities.Gases in Lenghu-3,-4,and-5,Eboliang,and Hulushan,were mainly sourced from the Kunteyi depression,among which gas in Lenghu-3 was generated by sapropel organic matter and those from Lenghu-4 and-5,Eboliang,and Hulushan,were sourced from humic organic material.Gases in Nanbaxian were derived from humic organic material in the Yibei depression;and those in Mabei was originated from such depressions like Yibei,Saishiteng,Yuqia,and Gaxi.