孔隙性砂岩中单条变形带与簇状变形带的特征与区别--以远安地堑上白垩统红花套组中变形带为例

Discussion on the characteristics and differences between single deformation bands and clusters of deformation bands in porous sandstone--Taking the deformation bands of Upper Cretaceous Honghuatao Formation in Yuan’an Graben as an example

孔隙性砂岩中的变形带研究近年来取得长足进展,但有关单条变形带与簇状变形带如何区分和界定仍是一个较模糊的问题。本文以远安地堑上白垩统红花套组高孔砂岩中发育的剪切增强压实带和压实剪切带为例,对单条及簇状变形带的特征和区别做出系统分析。研究表明,虽然单条变形带的长度、宽度、错断位移、凸起高度等均明显小于簇状变形带,但是不同运动学成因的变形带宏观特征、微观结构不同,因此不能单纯以规模大小区分二者,需要结合带密度将簇状变形带与变形带列、网格构造等相区分,还需要结合其微观结构特征进行准确鉴定。单条及簇状剪切增强压实带特征类似,均不具核心碎裂带,颗粒主要为中等破碎,多表现为多个不连续分布的碎裂核。簇状剪切增强压实带内部的非均质性更强。单条压实剪切带具有核心碎裂带,依剪切力大小不同,其核心碎裂带内颗粒粉碎程度及边缘过渡带宽度不同,常伴随微小剪切缝痕迹。簇状压实剪切带在镜下可清晰识别出不同的核心碎裂带、带间区域及微小剪切缝,可见S—C组构和断续分布的滑动面。单条及簇状变形带的发育会不同程度地改变储层的物性并可能会对油气运移和开采产生影响。

Objectives: Although the research on deformation band in porous sandstone has made great progress in recent years,it is still a relatively fuzzy problem to distinguish and define a single deformation bands and clusters of deformation bands. This paper clarifies this issue and discusses its influence on hydrocarbon migration and exploitation.Methods: Taking the shear-enhanced compaction bands( SECB) and compactional shear bands( CSB)developed in the high porosity sandstone of honghuatao formation of Upper Cretaceous in Yuan ’an Graben as examples,the characteristics and differences of single deformation band and clusters of deformation bands are systematically analyzed from macro and micro perspectives.Results: The results show that although the length,width,displacement and bulge height of the single deformation band are significantly smaller than those of the deformation band clusters,the characteristics of deformation bands of different kinematic types are different. SECB has no central cataclastic band,and the grains are mainly moderately fractured,and most of them are discontinuous cataclastic cores. The characteristics of single SECB and clusters of SECBs are similar,but the heterogeneity of SECB clusters is stronger,and the decrease of porosity and permeability is limited. A single CSB usually has a central cataclastic band. The degree of grain crushing and the width of the margin transitional band depend on the shear stress,and are often accompanied by micro shear fractures. Under the microscope,the clusters of CSBs can clearly be identified different central cataclastic bands, interband area and micro shear fractures, and occasionally, subtle S—C structures and discontinuous slip surface can be seen.Conclusions: It is not only necessary to distinguish single deformation band and clusters of deformation bands according to their scale,but also need to distinguish deformation band clusters from deformation band arrays and networks of distributed deformation bands according to their band density,and identify them accurately according to their microstructural characteristics. The deformation bands in porous sandstone will change the physical properties of reservoir and may have an impact on oil and gas migration and exploitation.