活动期断裂侧向封闭的地质条件及其研究方法

关于断裂侧向封闭的地质条件前人曾做过大量的研究和探讨,但相关研究均未考虑断裂带内部结构特征对断裂侧向封闭性的影响,致使活动期断裂的侧向封闭性少有被提及。为此,在断裂带填充物成分和结构特征分析的基础上,依据静止期断层岩侧向封闭机理,对活动期断裂侧向封闭的地质条件及其研究方法进行了探讨,指出活动期断裂侧向封闭的地质条件应是断裂为反向且断移地层以泥岩为主,才会形成断裂带填充物排替压力大于或等于油气运移盘储层岩石的排替压力,断裂侧向封闭。进而通过比较断裂带填充物排替压力与油气运移盘储层岩石排替压力的相对大小,建立了一套活动期断裂侧向封闭性的研究方法,并将其应用于渤海湾盆地南堡凹陷南堡1号构造F1、F2、F3这3条断裂的侧向封闭研究中。结论认为:(1)在天然气成藏期(新近系明化镇组沉积晚期)F1、F2、F3这3条反向活动断裂断裂带的填充物以泥质成分为主,且其排替压力分别大于古近系东营组一段(F1、F3)、新近系馆陶组(F2)储层岩石的排替压力,在侧向上对天然气均是封闭的,有利于天然气的聚集与保存;(2)分析结果与目前Np101井、Np1-2井、Np1井分别在东一段和馆陶组和钻获工业气流相吻合,表明将该方法用于活动期断裂侧向封闭性研究是可行的。

Geological conditions for lateral sealing of active faults and relevant research methods

Many researchers worked a lot on geologic conditions for lateral sealing of faults, but none of their studies took the effect of internal structures of fault zones on the lateral sealing capacity of faults. Therefore, the lateral sealing of active faults has rarely been discussed. In this paper, based on the analysis of the composition and structure characteristics of fault fillings, the geological conditions for lateral sealing of active faults and relevant research method were discussed in reference to the lateral sealing mechanisms of inactive fault rocks. It is shown that, in order to satisfy geologically the lateral sealing of active faults, the faults should be antithetic and the faulted strata should be mainly composed of mudstone, so that the displacement pressure of fault fillings is higher than or equal to that of reservoir rocks in oil and gas migration block. Then, a research method for the lateral sealing of active faults was established by comparing the displacement pressure of fillings in the fault with that of reservoir rocks in oil and gas migration block. This method was applied to three antithetic faults (F1, F2 and F3) in No.1 structure of the Nanpu Sag, Bohai Bay Basin. As revealed, the fillings of these three active faults were mostly argillaceous at the stage of natural gas accumulation (the late stage of Neogene Minghuazhen Fm sedimentation), and their displacement pressures were higher than that of reservoir rocks in the first member of Paleogene Dongying Fm (F1 and F3) and the Neogene Guantao Fm (F2). Accordingly, they are laterally sealed for natural gas, which is conducive to the accumulation and preservation of natural gas. Industrial gas flow has been produced from the first member of Paleogene Dongying Fm in Well Np101, the Guantao Fm in Well Np1-2 and the first member of Paleogene Dongying Fm in Well Np1, which is in agreement with the analysis result. It is verified that this method is feasible for investigating the lateral sealing of active faults.