常规砂岩与砂砾岩分形特征对比及成因分析:以乌石凹陷X构造流沙港组为例

Fractal Characteristics Comparison and Genesis of Conventional Sandstone and Glutenite

基于常规物性、铸体薄片、高压压汞等实验分析资料,运用分形理论研究乌石凹陷X油田始新统流沙港组常规砂岩与砂砾岩储层分形特征,分析分形曲线特征,分形维数及其与储层物性、孔隙结构参数之间的关系,评价分形维数对不同类型砂岩储渗能力表征的有效性。结果表明:相比常规砂岩,砂砾岩高压压汞分形曲线呈现分段特征,指示发育大孔、小孔、微孔三套尺度不同的孔喉系统,分段分形表征结果显示大孔与小孔分形维数大于常规砂岩,表明砂砾岩孔隙结构最复杂;常规砂岩分形维数与储渗性能相关参数关系较好,而砂砾岩样品分形维数仅与储集能力参数具有一定相关性。综上所述,研究区砂砾岩相比常规砂岩孔渗关系更复杂,孔隙类型多样,不同类型孔隙连通性差异较大,分形维数可表征其储集能力,但对渗流能力表征具有一定局限性。

Based on data from cast thin section,microscope,mercury-injection and conventional physical property analyses,we investigated the fractal characteristics of pore structure of glutenite reservoir developed in the Eocene Liushagang Formation of the Wushi Sag.The study includes the characteristics of fractal curves,fractal dimension and its relationship with reservoir physical properties and pore structure parameters,the effectiveness of fractal dimension in characterizing the storage and the permeability of different types of sandstones.The results show that compared with conventional sandstone,the high-pressure mercury fractal curve of glutenite presents has segmented features,indicating the development of three sets of pore-throat systems of different scales(macropores,small pores,and micropores).Segmented fractal characterization indicates that the fractal dimensions of large and small pores are greater than those of conventional sandstone.All the above analysis shows that the glutenite pore structure is the most complex.The fractal dimension of conventional sandstone has a good relationship with porosity and permeability,while the fractal dimension of glutenite samples has only a minor correlation with the storage capacity parameters.Hence,the glutenite has complex porosity-permeability relations,diverse types of pores and pore connectivity.The fractal dimension can characterize the reservoir capacity,but has certain limitation on seepage capacity characterization.