藏北羌塘盆地井下布曲组含油白云岩地球化学特征及其意义

    Geochemical features of oil-bearing samples from the well in Buqu Formation in the Qiangtang Basin, northern Tibet, and their implications

    • 摘要: 羌资11、12井是羌塘盆地揭示隆鄂尼-昂达尔错古油藏展布规律的资料井。对这2口钻井揭示的含油岩层进行取样分析,结合前人该区石油地质调查报告中羌资2井布曲组、夏里组及曲色组烃源岩的分析数据,从类异戊二烯烃、甾烷、萜烷等系列生物标志化合物参数方面进行油-岩对比研究。研究表明,羌资11、12井揭示的原油为同一种类型,但11井原油生物降解程度强于12井。各原油的母质主要来源于低等水生生物和藻类;各原油的母质形成于还原-弱还原、盐度值不高的咸水环境。原油中类异戊二烯烃、萜烷、甾烷等生物标志化合物参数与羌资2井布曲组泥晶灰岩与夏里组和曲色组烃源岩之间具有较好的亲缘性。结合南羌塘地区烃源岩有机碳资料,油源可能主要来自于曲色组,混入了部分夏里组及布曲组的油源,具有混源的特征。该研究结果对下一步油气勘探具有一定的指导意义。

       

      Abstract: The Qiangzi-11 and 12 wells are the data well to reveal the distribution regularities of Longeni-Angdaerco palaeo-oil reservoirs. Together with the hydrocarbon source rock data of Buqu Formation, Xiali Formation, and Quse Formation from Qiangzi-2 well, the authors analyzed the oil-rock correlations based on the biomarker parameters composed of isoprenoid, steranes, and ter-panes. The property of crude oil from Qiangzi-11 and 12 wells is of the same type. However, the biodegradation degree from Qiang-zi-11 well is higher than that from Qiangzi-12. The biomarker parameters reveal that the organic matter mainly originated from al-gae. The crude oil was formed under weak reduction-reduction conditions and in a slightly salty water environment. The biomarkers of crude oil, composed of isoprenoid, terpane, and sterane, are closely related to those of the Buqu Formation in Qiangzi-2 well, and also show good correlation with those of the Xiali Formation and Quse Formation in Qiangzi-2 well. Combined with the TOC data of the hydrocarbon source rock in south Qiangtang Basin, the authors hold that the crude oil of the Longeni-Angdaerco palaeo-oil reservoir was mainly from the source rocks of Quse Formation, and partly from the Xiali and Buqu Formations, suggesting a mixture of sources. The result of this study may have some guidance significance for further oil-gas exploration.

       

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