Abstract: This study focuses on the disaggregation band developed in porous sandstone formations, systematically analyzes its deformation mechanism, formation conditions, and internal structure characteristics. and finally clarifies the sealing capacity of the disaggregation band and its role in hydrocarbon migration and preservation. The results show that the disaggregation mainly occurs during the faulting deformation of porous sandstone (with a porosity of less than 15 %) in unconsolidated to semi-consolidated diagenetic stages, which leads to the rotation, rolling and directional rearrangement of sandstone particles in the fault zone, thus forming the disaggregation band. The formation of disaggregation band is jointly controlled by clay content, porosity, and burial depth of sandstone. Specifically, the porous sandstone with a clay content of less than 15 % can form a disaggregation band when faulting deformation occurs under shallow burial depths (less than 1 000 m) and low effective stress. The field outcrop observations confirm that the disaggregation band has a typical binary structure that consists of both disaggregation-dominated fault core and damage zone, and generally demonstrates high permeability, and its porosity and permeability are not much different from or slightly higher than those of the host rock. Under the low-displacement condition where the single-layer sandstone is not completely offset, the synthetic disaggregation band has no sealing capacity, and serves as a channel for lateral hydrocarbon migration; the fault trap mainly develops at the segmental growth point of hanging wall of fault, which makes it difficult to form lithological juxtaposition sealing. The antithetic fault trap develops at the foot wall of fault, and can form lithological juxtaposition sealing. The evaluation process for the hydrocarbon preservation capability of disaggregation fault traps is demonstrated as follows. Firstly, the types of fault traps are determined according to the configuration between formation and fault occurrences. Then, the sealed hydrocarbon column height is evaluated using the lithology juxtaposition diagram and fault triangle diagram. Finally, the destructive effect of fault reactivation on hydrocarbon preservation is analyzed using the fault juxtaposition thickness or shale smear factor.

Key words: disaggregation falut zone, faulting mechanism, internal structure, sealing capacity, migration and preservation

摘要： 以孔隙性砂岩地层发育的解聚型断层带为研究对象,通过系统分析其变形机制、形成条件及内部结构特征,明确了解聚型断层带的封闭性及其在油气运移和保存中的作用。研究结果表明,处于未固结—半固结成岩阶段的孔隙性砂岩(孔隙度＞15 % ),其在断裂变形时主要发生解聚作用,可导致断层带内的砂岩颗粒旋转、滚动并定向重排,形成解聚带;岩石的泥质含量、孔隙度及埋深等因素共同控制着解聚带的形成,其中,泥质含量＜15 % 的孔隙性砂岩在埋深＜1 000 m、低有效应力作用下通常在发生断裂变形时可形成解聚带。野外露头证实,解聚型断层带一般具有典型的"二元结构",即由解聚型的断层核和解聚带发育的破碎带组成。解聚型断层带往往具有高渗透性,其岩石的孔隙度和渗透率与未变形岩石相差不大或略有升高。在单层砂岩未被完全错断的低断距条件下,同向解聚型断层带不具备油气封闭能力,是油气侧向运移的通道,断层圈闭主要发育在断层上盘断裂分段生长的连接点处,难以形成岩性对接封闭;反向断层圈闭发育于断层下盘,可形成岩性对接封闭。解聚型断层圈闭的油气保存能力评价流程为:首先,根据地层产状与断层产状的配置关系确定断层圈闭的类型;然后,利用断层面岩性对接图和断层三角图解评价出封闭的烃柱高度;最后,利用断接厚度或泥岩涂抹系数等方法分析断层再活动对油气保存的破坏作用。

关键词: 解聚型断层带, 变形机制, 内部结构, 封闭性, 运移和保存