东营凹陷古近系超压封闭层特征及其封盖能力研究

摘要

Observed pressure reveals that overpressure is widely developed in the Paleocene in Dongying Depression,Eastern China.According to logging responses of overpressure mudstones,the vertical distribution of overpressure seal is identified.On this basis,its petrological characteristics and sealing ability were systematically studied.The result shows that the burial depth for the Paleocene overpressure seal top is mainly 2 400~2 800 m and became shallower from the center to edge of the sag and the central uplift in the plane.The lithological composition of the overpressure seal is formed by a group of dark gray mudstone,calcareous mudstone and sandy mudstone,of which the average sand-clay ratio is 0.092,the thickness is 500~900 m and the maximal thickness of the single mudstone is greater than 10 meters.Whole rock X-ray diffraction shows that the mudstones of the pressure seal contain large amounts of carbonate minerals and clay minerals.Mudstone diagenesis reaches the rapid transformation of the illite-montmorillonite interlayer minerals,and corresponds to the mass carbonate minerals during the first and second stage.The overpressure seal could close surplus pressure greater than 14 MPa,which had a close relation with high displacement pressure(average 5.45 MPa).Besides,thickness and diagenetic grade of the overpressure seal are important influencing factors for its sealing ability.%东营凹陷古近系地层的超压现象十分普遍。依据超压区泥岩的测井响应特征,分析了封闭层在纵向上的分布,并在此基础上对其岩石学特征及封盖能力进行了系统研究。结果表明：超压封闭层的埋深主要为2400～2800m,在平面上表现为洼陷中心深而洼陷边缘和中央隆起带浅的特征;其岩性为一套深灰色泥岩、灰质泥岩和砂质泥岩的组合,厚度为500～900m,砂泥比平均值为0.092,单层泥岩的最大厚度大于10m。全岩矿物的X射线衍射分析表明,组成封闭层的泥质岩中含有大量的碳酸盐矿物和黏土矿物,泥岩的成岩作用发生在伊/蒙混层矿物的迅速转化期,且对应于第一期和第二期碳酸盐的大量产出段。超压封闭层能封闭剩余压力大于14MPa的超压,这与其具有较高的排替压力（平均为5.45MPa）密切相关,此外封闭层的厚度及成岩作用的强度也是影响其物性封盖能力的重要因素。