藏北羌塘盆地角木茶卡地区下二叠统展金组烃源岩特征及意义

Characteristics and significance of the source rocks from the Lower Permian Zhanjin Formation in the Jiaomuchaka area, Qiangtang Basin, northern Xizang

关键词:  羌塘盆地  角木茶卡地区  烃源岩  展金组  早二叠世

Key words:  Qiangtang Basin  Jiaomuchaka  source rock  Zhanjin Formation  Early Permian

摘要:

在羌塘盆地中央隆起带附近角木茶卡南发现一套下二叠统展金组含凝灰质烃源岩。依据露头样品和测试数据,从有机质丰度、有机质类型及成熟度方面对这套烃源岩特征进行了研究。研究结果表明,展金组烃源岩有机碳含量在0.35%~0.98%之间,达到了烃源岩标准,且大部分接近中等烃源岩标准;通过干酪根镜鉴、干酪根元素分析、干酪根碳同位素等结果分析,其有机质类型主要为Ⅱ₂-Ⅲ型;有机质镜质组反射率Ro为1.54%~1.59%,岩石热解峰温T_max介于467~530℃之间,干酪根腐泥组颜色为棕黄色,显示有机质热演化处在高成熟阶段。研究结果显示该套烃源岩具有较好生烃潜力,在以后的勘探中要予以重视。

Abstract:

The tuffaceous source rocks are found to be hosted in the Lower Permian Zhanjin Formation in the Jiaomuchaka area near the central uplift of the Qiangtang Basin,northern Xizang. The integration of abundance, type and maturity of the organic matter in this study has disclosed that the total organic carbon contents in the tuffaceous source rocks range between 0.35% and 0.98%, within the limits of standards coming up to the medium-grade maturity of source rocks. The microscopic examination and element and carbon isotope analyses for the kerogens indicate that the organic matter types are represented by sapropel-humic (II₂ type) and humic (III type). The vitrinite reflectances (Ro) for the source rocks vary from 1.54% to 1.59%. The pyrolytic peak temperatures (T_max) range between 467 and 530℃. Meanwhile, the sapropelinite in the kerogens exhibits brownish yellow in colour. The above-mentioned results show that the thermal evolution of organic matter has now reached up to the higher maturity levels of the source rocks, and thus the source rocks have good hydrocarbon-generating potential in the study area.