青藏高原比如盆地中-上侏罗统烃源岩

Source rock features of the middle-upper Jurassic Lagongtang Formation in Biru Basin,Tibet Plateau

比如盆地中-上侏罗统拉贡塘组以一套半深海—深海相浊积沉积体系为主,不完整的鲍玛序列为其标志性沉积构造。通过对残留盆地不同部位观测点数据统计、样品测试与分析,认为拉贡塘组烃源岩累计厚度巨大,有机质类型以Ⅰ型与Ⅱ1型为主,有机质丰度较高,TOC主峰分布在0.40%～1.20%;拉贡塘组有机质Ro主峰分布在2.0%～5.0%,处于高—过成熟演化阶段。对拉贡塘组烃源岩热演化指标Ro偏高的原因进行探讨,初步认为特提斯构造域独特的构造演化背景下,中生界的褶皱、堆垛加厚,以及燕山期—喜山期岩浆、热液等方面作用,引起中生界区域变质作用与局部构造变质作用,很可能是导致中生界有机质高演化及其出现演化程度地区性差异的重要因素。由此提出,青藏高原油气勘探与评价应注重喜山期构造演化对油气富集与保存的研究。

The middle-upper Jurassic Lagongtang Formation,composed mainly of a turbidite depositional system of bathyal-deep sea facies,is characterized by an incomplete Bouma sequence.The statistic data of observations at different parts of the residual basin as well as the measurement and analysis on source rock samples showed that the Lagongtang Formation source rock had a huge accumulative thickness and contained organic matter dominated by typeⅠand type Ⅱ1 kerogens.The source rock was characterized by abundant organic matter with TOC mostly ranging from 0.40% to 1.20%,and a high or even over maturity with Ro mainly varying between 2.0%～5.0%.Under special evolutionary settings of the Tethys tectonic domain,the regional metamorphism and local structural deformation arising from the Mesozoic folding,stacking,thickening and the Yanshanian-Himalayan magmatic and hydrothermal alterations were likely to be the important factors that gave rise to high maturity of the Mesozoic organic matter and regional differences in maturity.Therefore,the paper suggested that the prospecting and assessment on hydrocarbon resources in Tibet Plateau should focus on the influence of the Himalayan tectonic evolution on oil-gas accumulation and preservation.