四川盆地北部须家河组裂缝发育特征与控制因素——以广元和旺苍地区地表露头为例

Characteristics of Fracture Development and Its Controlling Factors of Xujiahe Formation in the North of Sichuan Basin ——A Case Study of Outcrops in Guangyuan and Wangcang Areas

对四川盆地北部广元和旺苍地区典型露头区须家河组(T3x)裂缝进行了系统观察和测量,该地区普遍发育构造剪切缝,包括高角度剪切缝、斜交缝和低角度剪切缝共3种类型。裂缝多与层面呈高角度相交,工农镇地区裂缝优势走向为近EW向、NW向和近SN向,离妻岩地区裂缝优势走向为近EW向。控制广元和旺苍地区T3x露头区裂缝发育程度主要因素有岩性、层厚及岩性组合。细砂岩和粉砂岩中裂缝密度最高,粗砂岩和砾岩中裂缝密度较低;裂缝密度与力学层厚度之间呈幂函数关系,随着岩层层厚增加,裂缝密度逐渐降低,厚层中裂缝发育程度较差;不同岩性组合中,砂泥岩互层、泥岩层中的薄-中层砾岩段裂缝较发育。

The outcrop fractures of Xujiahe Formation in Guangyuan and Wangcang Areas in the North of Sichuan Basin were carefully observed and surveyed in this study.The major fracture types were tectonic shear fractures,including high angle shear fractures,dipping fractures and low angle shear fractures.There were approximate east-west,northwest-southeast and approximate north-south tectonic fractures with high angle to major bedding surfaces.The development of fractures was mainly controlled by the lithology,stratum thickness,and lithologic association in Xujiahe Formation.Fracture density in fine sandstone and siltstone was the largest,while fracture density in course sandstone and conglomerate was lower.There is a negative exponent relationship between the fracture density and strata thickness.The development degree of the fracture decreases with the increase of strata thickness with poor development of fractures in thick layers.Fractures are developed in sandshale interbedded layers and in the combination of thin-middle conglomerate layers