伸展构造区低渗透储层构造裂缝的分布特征

本文以辽河盆地雷家沙四段白云岩储层为例,研究了伸展构造区低渗透储层裂缝的分布特征,根据裂缝的分布形式,可将储层中的裂缝分为层间裂缝、穿层裂缝和顺层裂缝3种类型,其中层间裂缝的分布严格受白云岩控制,与层面垂直,并终止于层面上,而穿层裂缝呈高角度与层面斜交,在剖面上,单条裂缝呈现"平面"式、"铲形"式和"坡坪"式分布,多条裂缝呈"堑垒"式和"多米诺"式等组合形式,即表现出与区内伸展正断层相一致的分布特征,它们和正断层一起构成了区内伸展构造从大到小、从宏观至微观的完整构造样式。储层中裂缝的分布受岩性、层厚及断层等因素的控制。在白云岩储层的泥质夹层中,由于穿层裂缝及顺层裂缝发育,它们相互沟通,并和白云岩中的裂缝一起构成了储层中三维裂缝网络系统,使泥质夹层不起真正的隔层作用,可划分为准储层,从而使该白云岩油藏具块状特征。在伸展断层附近,断层上盘的裂缝较下盘更发育,并表现出较好的分带性。

DISTRIBUTION CHARACTERISTICS OF FRACTURES IN LOW PERMEABLE RESERVOIRS IN AN EXTENSIONAL STRUCTURAL REGION

The dolomite reservoir of Sha 4 Member in Leijia Formation,Liaohe basin is taken as an example to study the distribution characteristics of fractures in low permeable reservoirs of an extensional structural region.Three distributive types of fractures are identified,i.e.internal,transverse and bedding fractures,of which internal fracture is strictly controlled by dolomites,perpendicular to and terminated onto the bedding plane;whereas transverse fracture is in a high-angle oblique to bedding plane.On a section,a mono-fracture appears planar,listric and ramp-flat;and multi-fractures may be in a combined pattern of grabenuhorst or domino,showing a consistent distribution with the growth normal faults in the region.Fractures and normal faults will constitute a complete structural style of an extensional structure within the region,ranging from macroscope to microscope in scale.The distribution of fractures in a reservoir is controlled by the factors of lithology,bed thickness and faults,etc.Transverse and bedding fractures are well developed in the argillaceous interlayers of dolomlte reservoirs,and are interconnected;together with fractures in the dolomites,they make up a 3-D fracture network.As a result,the argillaceous interlayers can not be taken as impermeable layers but para-reser-voirs instead,and thus the dolomite oil reservoirs are characteristic of block.Toward an extensional fault,the fractures in the lianging wall are more developed than those in the footwall with good zonation.