下扬子复杂构造区超高压含气层的发现及油气富集关键要素

    Discovery of overpressure gas reservoirs in the complex structural area of the Lower Yangtze and its key elements of hydrocarbon enrichment

    • 摘要: 下扬子地区的构造复杂性使该地区油气勘探存在极大的难度和风险,如何在复杂构造区取得油气勘探突破是近年关注的焦点。2019年皖为页1井在下扬子无为凹陷三叠系周冲村组首次发现2套异常高压含天然气层,最高地层压力系数达1.9,取得下扬子油气调查的重大突破性进展,为下扬子油气勘探困局打开了一扇窗口。基于该超压含气层的新发现,综合研究表明,无为凹陷天然气富存得益于4个关键控制要素的有机组合:①深层稳定基底;②对冲过渡带原地体;③深水裂陷黑色页岩有利相带;④多套膏盐有利封盖等。为无为凹陷提供了稳定构造背景、良好构造保存、有利烃源岩及优质盖层等条件。上述地质要素同样有利于该凹陷二叠系页岩气富集,由此提出了构造复杂区三叠系常规天然气与二叠系页岩气一井双探的新思路。上述关键4个要素在下扬子区域上的配置关系显示,望江凹陷与无为凹陷具有相似的地质条件,是下一步油气勘探的首选有利区。

       

      Abstract: The complexity of the structure in the Lower Yangtze area makes it very difficult and risky to explore for oil and gas in this area.How to make a breakthrough in oil and gas exploration has been the focus of attention in recent years.In 2019, two sets of abnormal high-pressure natural gas layers were firstly discovered in the Triassic Zhouchongcun Formation in Wuwei depression of the Lower Yangtze.The pressure coefficient reached 1.9, which was the highest one in East China.This new discovery made a significant breakthrough in the oil and gas exploration and proved the good resource prospect in the lower Yangtze.The new discovery of the overpressure gas reservoir reveals four key control factors for natural gas enrichment in Wuwei depression, namely deep stable basement, intracontinental in-situ block, favorable facies zones of black shale, multiple layers of anhydrite, and favorable source rock and good capping conditions, which provide stable tectonic setting, good structural preservation, favorable source rock and good capping conditions for oil and gas.The above geological factors are also conducive to the Permian shale gas enrichment in Wuwei depression.Accordingly, a new idea of conjoint exploration of Triassic conventional natural gas and Permian shale gas in one well is put forward.Finally, the configuration of the above four key elements in the Lower Yangtze region suggests that Wangjiang depression shares similar geological conditions with Wuwei depression, which making it a next priority for oil and gas exploration.

       

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