高演化地区古油藏Re-Os年代学与REE特征分析——以南盘江盆地板街古油藏为例

Re-Os chronology and REE analysis of paleo-oil reservoir in high evolution areas: a case study of Banjie paleo-oil reservoir, Nanpanjiang Basin

谭笑林 胡煜昭 周亮 程涌 李丕优

TAN Xiaolin HU Yuzhao ZHOU Liang CHENG Yong LI Piyou

昆明理工大学 国土资源工程学院, 昆明 650093 中国石油大学 地球科学学院, 北京 102249 云南省矿产资源预测评价工程实验室, 昆明 650093

Faculty of Land and Resource Engineering, Kunming University of Science and Technology, Kunming, Yunnan 650093, China College of Geosciences, China University of Petroleum (Beijing), Beijing 102249, China Yunnan Mineral Resources Laboratory, Kunming, Yunnan 650093, China

由于高演化地区传统有机指标受到较大影响，在该类地区的油源对比研究中结合REE这一无机指标，将增加其结果的准确性。此外，储层沥青Re-Os测年作为一种定量的年代学研究手段，测试结果代表意义一直存在争议。对南盘江盆地板街古油藏储层沥青进行了稀土元素地球化学分析和Re-Os测年，并将其稀土元素配分模式与区内主力烃源岩通过灰色关联法进行了对比分析。南盘江盆地板街古油藏储层沥青中稀土总量较低，轻重稀土分馏明显，呈现为弱的Ce负异常和明显的Eu负异常，表明沥青形成时处于还原环境且未经历过强烈的风化淋滤作用，稀土配分模式属于轻稀土富集右倾模式；其稀土元素配分模式曲线与区内泥盆系烃源岩相似，二者具有成因关系。Re-Os测年结果显示，板街古油藏沥青Re-Os模式年龄主要分布于(203.6±1.1)~(238.5±4.2) Ma，平均(224.8±3.3) Ma(n=7)；最后一次扰动该沥青Re-Os时间体系的因素是生成沥青的过程，该模式年龄代表了板街古油藏储层沥青形成即原油裂解成气的时代。

The traditional organic index can be greatly affected in the areas with high thermal evolution degree whilst combination of REE for oil-source correlation will improve the results. In addition, Re-Os dating is a quantitative method of geochronology, but the significance of the test results is quite controversial. In this paper, REE geochemical analysis and Re-Os dating of bitumen in the Banjie paleo-oil reservoir is carried out. The REE distribution pattern of bitumen was compared with that of the main source rocks in the area using the method of grey correlation. Results show that the ΣREE of bitumen in the Banjie paleo-oil reservoir is low, and the fractionation of light and heavy REEs is obvious, showing a weak negative Ce anomaly and an obvious negative Eu anomaly, which indicates that the bitumen was formed in a reducing environment and has not experienced any strong weathering or leaching. The REE distribution mode belongs to the right-leaning mode of LREE enrichment. The REE distribution pattern curve is similar to that of Devonian source rocks in this area, indicating a genetic relationship. The results of Re-Os dating show that the Re-Os model age of bitumen in the Banjie paleo-oil reservoir ranges mainly from (203.6±1.1) Ma to (238.5±4.2) Ma, with an average of (224.8±3.3) Ma (n=7). The last factor which disturbed the Re-Os system of the bitumen is the process of bitumen generation. The model age represents the age of bitumen formation in the Banjie paleo-oil reservoir, when oil was cracked into gas.

国家自然科学基金项目 41672073

https://doi.org/10.11781/sysydz202205877