低渗透砂岩油藏注水诱导裂缝特征及其识别方法——以鄂尔多斯盆地安塞油田W区长6油藏为例

在总结注水诱导裂缝概念的基础上，阐明了注水诱导裂缝的基本特征及形成机理，提出了识别注水诱导裂缝方法，最后利用该方法对鄂尔多斯盆地安塞油田W地区长6油藏A0井组的注水诱导裂缝进行了识别。注水诱导裂缝为张性裂缝，其规模大、延伸长，渗透率高，纵向上不受单层控制，延伸方位一般与现今地应力的最大水平主应力或者油藏主渗流裂缝方向一致，并随着低渗透油藏注水的推进发生动态变化。长期注水开发过程中，若油井逐渐表现出方向性水淹且含水率变化曲线呈现出阶梯状上升，试井解释具有裂缝渗流特征，同时水淹井对应的注水井吸水剖面逐渐表现为指状吸水且注水指示曲线出现拐点，示踪剂或水驱前缘监测油水井之间表现出良好的连通关系，则可判定在油水井之间形成了注水诱导裂缝。

Characteristics of waterflood induced fracture in low-permeability sandstone reservoirs and its identification methods:A case study from Chang 6 reservoir in W area in Ansai oilfied,Ordos Basin

This paper introduces the principles of waterflood induced fracture,clarifies their basic characteristics and proposes the methods to identify them.Then the waterflood induced fracture of Well A0 group of Chang 6 reservoir in W area in Ansai oilfield,Ordos Basin has been identified by these methods.With larger scale,long extension and high permeability,waterflood induced fracture are tension fractures which are not controlled by single stratum in vertical extension.Their trend direction are generally along the present maximum horizontal principal stress or the main seepage fracture direction.In a long term waterflooding process,the following are clear indications for the establishment of waterflood induced fracture between producer and injector wells:if the oil wells shows a gradually dominant direction of flooding,the water-cut curve presents step-type rise,well test interpretation has the character of fracture seepage,the water injection profile of the injection well gradually presents finger-like water absorption characteristics,inflection point appears in water injection index curve,tracer or water flooding front monitoring showed good connectivity between wells.