从内部结构出发探讨断裂控藏机理及模式:以珠江口盆地珠一坳陷为例

Mechanism and Model of Fault Controlling Reservoir in Terms of the Internal Structure of Fault Zones:Examples from Zhu Ⅰ Depression,Pearl River Mouth Basin

断层是珠一坳陷油气成藏重要的控制因素。从断裂带内部结构出发，通过认识断层核及破碎带特征和差异性，进而分析断层输导与封闭的机制。综合分析表明：①断移期与过渡期断层输导油气的机制有所不同，断侈期主要沿滑动面和伴生缝以“地震泵”形式垂向输导，侧向分流受控于断层末端未被断穿的厚层泥岩；过渡期主要沿破碎带中的诱导裂缝以浮力流或渗流的方式垂向输导，侧向分流在多套泥岩的遮挡下均会产生分流。②断层封闭又分为垂向封闭和侧向封闭。垂向封闭首先取决于泥岩塑性变形的连续性，珠一坳陷新近系断层错断泥岩的SSF值为5，当SSF值小于5时，泥岩连续垂向封闭；当SSF值大于5时，只有当断层核及破碎带中的通道均无法连通时，垂向才封闭。侧向封闭包括对接封闭和断层岩封闭2种形式．对接封闭依赖于泥岩的塑性变形；断层岩封闭取决于断层岩的岩性、厚度及物性。在断裂带内部结构和断裂控藏机制认识的基础上，总结了珠一坳陷4种（Ⅰ～Ⅳ）断裂控藏的模式，分别为上盘输导上盘成藏型、下盘输导下盘成藏型、侧向遮挡成藏型与组合控藏型，并通过实例进行了详细解析。综合认为，Ⅰ型为珠一坳陷最有利的成藏类型．Ⅲ型和Ⅳ型其次，Ⅱ型发现较少。

Fault is an important control factor for hydrocarbon accumulation in Zhu I Depression. In terms of the internal structure of fault zones, this paper analyzes fault migration and sealing mechanism through understanding the characteristics and differences of fault zone and fracture zone. The analysis suggests that fault migration mechanism is different in faulting period and transition period. In the faulting period, the vertical migration mainly occurs in sliding surface and induced fractures in the form of ＂seismic pump＂, and the lateral migration is controlled by unbroken thick mudstone upon fault tip. While in the transition peri- od the vertical migration mainly occurs through induced fractures in fracture zone in the form of buoyant flow and seepage, and the lateral migration can occur under any mudstone broken by the fault. Fault seal can be divided into vertical and lateral seals. Vertical seal is primarily determined by continuity of plastic deformation of mudstone. Zhu I Depression Neogene SSF critical value of faulted mudstone is 5, when SSF is less than 5, mudstone maintain continuous and fault is vertically sealing. However, when SSF is more than 5, only when fauh： core and fracture zone have no connected paths, the fault is vertically sealing. Lat- eral seal consists of juxtaposition seal and fault rock seal, with the former depending on the plastic deform- ation of mudstone and the latter being determined by the lithology, thickness and physical property. On the basis of internal structure of fault zones and mechanism of fault controlling reservoir, this paper sum- marizes four types of reservoir-controlling model： hanging wall migration and hanging walt accumulation, foot wall migration and foot wall accumulation, lateral sealing accumulation and multiple factors control- ling accumulation. These models are detailedly analyzed by examples. Based on comprehensive analysis, type I is the most favorable accumulation type of the Zhu Ⅰ Depression, followed by typeⅢ and type Ⅳ, and type Ⅱ is rarely found.