柴达木盆地北缘天然气成因类型及气源判识

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

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。

Based on the analyses of chemical components and carbon isotopic composition of 35 natural gas sam- ples from the Tertiary and Cretaceous reservoirs in 9 fields or trap structures in the northern edge of Qaidam Ba- sin, we defined indexes for identifing genetic types of gas, determined the thermal evolutionary stages, and identi- fied 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 Yikeyawu- ru, Nanbaxian, Lenghu-5, Eboliang and Mabei are of coal-type gas ; several gas samples from Mabei and Lenghu- 3, Lenghu4 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 Lenghu4 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 or- ganic 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.