泥岩盖层内断层垂向封闭能力综合定量评价:以南堡凹陷5号构造东二段泥岩盖层为例

为了更加准确地评价盖层内断层垂向封闭能力,在利用实验验证岩石各向异性对排替压力影响的基础上,结合断层岩与储层岩石的力学分解关系,综合考虑不同类型岩石压实成岩时间对排替压力的影响,对断层垂向封闭的断-储排替压力差法进行改进,并以此来定量评价渤海湾盆地南堡凹陷5号构造F_(np5-3)和F_(np5-5)两条主要断层的垂向封闭能力。研究结果表明:存在一个断-储排替压力差封油气下限值,只有当断层岩排替压力大于储层岩石排替压力且二者差值大于等于封油气下限值时,断层垂向封闭。由此确定反向断层F_(np5-3)的封油气下限值为0.221 MPa,顺向断层F_(np5-5)的封油气下限值为0.311 MPa;受油气富集部位及断裂带内部结构发育特征的影响,反向断层较顺向断层更易形成封闭,此评价结果与油气分布规律吻合关系较好。而利用改进前方法得到的评价结果(断层垂向不封闭)与实际钻井含油气性相矛盾,表明改进后方法在综合定量评价断层垂向封闭能力时的合理性与可行性。

Comprehensive Quantitative Evaluation of Vertical Sealing Ability of Faults in Caprock: An Example of Ed2 Mudstone Caprock in Nanpu Sag

To accurately evaluate the vertical sealing ability of the faults in caprock,based on the experiment of verifying the influence of the rock anisotropy and the mechanical relation of the displacement pressure of the fault rock and the reservoir rock in different directions,we improved the pressure-difference method to evaluate the fault sealing ability,and further analyzed the vertical sealing ability of the main faults Fnp5-3 and Fnp5-5 in 5th structure of Nanpu sag in the Bohai Bay basin,in combination with the differences in diagenetic time of different rocks,as well as the influence of the rock anisotropy on displacement pressure.The results indicate that:there is a low limit of displacement pressure difference between the fault rock and the reservoir rock,and only if the displacement pressure of the fault rock is larger than that of the reservoir rock,and the difference between the above two is larger than or equal to the low limit,then the faults seal vertically.From this,it is determined that the low limit of the reverse fault Fnp5-3 is 0.221 MPa,and the low limit of the forward fault Fnp5-5 is 0.311 MPa.Influenced by the accumulation of oil-gas and the characteristics of the fault internal structure,reverse faults are more likely to seal than forward faults.This is coincided well with the pattern of oil-gas accumulation;while the evaluation results obtained by the previous method without considering the above factors are inconsistent with the actual drilling oil-gas results.The improved method is reasonable and feasible for a comprehensive evaluation of the fault vertical sealing ability.