柴西油砂山地区油砂有机地球化学特征研究

Organic geochemical signatures of the oil sands from the Youshashan area, western Qaidam Basin, Qinghai

关键词:  油砂  地球化学  母质类型  沉积环境  成熟度

Key words:  oil sands  geochemistry  parent type  sedimentary environment  maturity

摘要:

为深入研究油砂山地区油砂的古沉积环境、成熟度及母质来源,促进柴西地区非常规资源勘探开发,本文以油砂山干柴沟组油砂为研究对象,通过气相色谱-质谱分析,发现该区油砂正构烷烃受到轻度损失,降解程度为1级;该区油砂具有低的m(Ts)/m(Tm)值,相对低的m(C₂₉ ββ)/m[(ββ+αα)]和m(C₂₉ ααα-20S)/m[20(S+R)]的值,表明油砂油属低成熟油砂油;m(Pr)/m(Ph)较低,表明其源岩沉积强还原环境;油砂油样品具较高的m(r-蜡烷)/m(0.5C₃₁)值,显示为高盐度咸水环境沉积;甾烷C₂₇、C₂₈和C₂₉参数成"L冶型或"V冶型分布,表明油砂油母质来源水生生物相对较多。

Abstract:

The oil sands resources are interpreted as the significant unconventional oil and gas resources in China. The emphasis of the present paper is placed on the chromatographic analysis and mass spectrographic analysis of eight pieces of oil sands samples from the Upper Ganchaigou Formation (N₁) in the Youshashan area in order to examine ancient sedimentary environments, maturity and origin of parent matter types. The results in this study show that the saturated hydrocarbons range between 0.53 and 0.81, indicating higher oil contents. The m (Pr)/m (Ph) ratios vary from 0.43 to 0.26, with an average of 0.32 (8), indicating a relatively deep-water and highly reducing environment of the source rocks. The parameters for oil sands evolution m[C₃₁αβ22S/22 (S + R)] and m[C₃₂αβ22S/22 (S + R)] are more than 0.5 or 0.6, indicating that all the eight oil sands samples are maturated oil sands samples and subjected to biodegradation. The triangular diagram of the parameters of steranes C₂₇, C₂₈ and C₂₉ indicate that the parent matter types of the oil sands belong to the lower aquatic organisms mixed with higher plants. The oil sands in the study area have higher contents of saturated hydrocarbons, wider outcropped area and greater thickness, and thus may be considered highly prospective for the unconventional oil and gas resources.