致密砂砾岩储层孔隙结构及分形特征

Pore Structure and Fractal Characteristics of Tight Glutenite Reservoir

摘要: 针对上乌尔禾组致密砂砾岩储层孔隙结构认识不清的问题，通过岩石化学分析数据统计、薄片观察，同时采用扫描电镜、高压压汞、氮气吸附等测试手段和方法，对上乌尔禾组致密砂砾岩储层微观孔隙结构特征进行研究，发现储集空间以粒间溶孔、粒内溶孔、晶间微孔、微裂缝等次生孔隙为主，部分孔隙、微裂缝已被不同程度充填。利用氮气吸附对储层微观孔喉进行分析，发现微纳米级储集空间较多，且一端封闭型孔隙、孤立孔隙和更加复杂的孔隙，对于油气的解析与运移不利，孔喉连通性差。根据压汞曲线形态及孔隙结构参数将致密砂砾岩储层孔隙结构分为4种类型，且孔隙结构越差，分形维数越高，同时样品分形维数会出现拐点，将样品中大孔与小孔分开，且拐点出现的位置是主要的孔隙半径，因此利用孔隙结构的分形特征可以为后期孔隙结构的定量评价提供基础。溶蚀作用对储层孔隙结构具有改善作用，增加了储层孔隙的连通性，充填作用、压实作用在一定程度上降低了储层渗流有效性。上乌尔禾组致密砂砾岩储层孔隙结构复杂，广泛发育微裂缝的贡献应引起重视。

Abstract: Aiming at the problem of unclear understanding of the pore structure of the tight glutenite reservoirs in the Upper Wuerhe Formation, through petrochemical analysis data statistics, thin section observations, scanning electron microscopy, high-pressure mercury intrusion, nitrogen adsorption and other testing methods are used. The microscopic pore structure characteristics of tight glutenite reservoirs in the Upper Wuerhe Formation were studied, and it was found that the reservoir space is dominated by secondary pores such as intergranular dissolved pores, intragranular dissolved pores, intercrystalline micropores, and microcracks. The micro-cracks have been filled to varying degrees. Using nitrogen adsorption to analyze the microscopic pore throat of the reservoir, it is found that there are many micro-nano-level storage spaces, and one end of closed pores, isolated pores and more complex pore structures are unfavorable for the analysis and migration of oil and gas, and the pore throat connectivity is poor. According to the shape of mercury injection curve and pore structure parameters, the pore structure of tight glutenite reservoirs is divided into 4 types, and the more the pore structure is, the higher the fractal dimension will be. At the same time, the fractal dimension of the sample will have an inflection point to differentiate the large pores and small pores in the sample. The position where the inflection point appears is the main pore radius. Therefore, the use of the fractal characteristics of the pore structure can provide a basis for the quantitative evaluation of the later pore structure. The dissolution can improve the pore structure of the reservoir and increase the connectivity of the reservoir pores. The filling and compaction effects reduce the effectiveness of reservoir seepage to a certain extent. The tight glutenite reservoir of Upper Wuerhe Formation has a complex pore structure and the contribution of extensively developed micro-fractures should be paid attention to.