He Taping, Zhou Yaoqi, Li Yuanhao, Xie Huanyu, Shang Yuehan, Chen Tongtong, Zhang Zhenwei
Key Laboratory of Geological Safety of Coastal Urban Underground Space, Qingdao Geo-Engineering Surveying Institute, Ministry of Natural Resources, Qingdao, 266101, China.
School of Geosciences, China University of Petroleum ( East China ), Qingdao, 266580, China.
Sci Rep. 2024 Oct 1;14(1):22825. doi: 10.1038/s41598-024-74101-4.
The pore-throat structure is a crucial parameter for evaluating reservoir characteristics and assessing the potential of oil and gas resources. Understanding the relationship between reservoir pore-throat variations and oil-bearing properties is essential. Through a combination of techniques, including thin-section casting, scanning electron microscopy (SEM), micro-computed tomography (micro-CT), and high-pressure mercury injection (HPMI), we examined the tight sandstone reservoirs from the Chang 4 + 5 members of the Yanchang Formation in the study area. This analysis elucidates the relationship between the pore-throat structure and fractal characteristics of the samples and their oil-bearing properties. The results show that : (1) The tight sandstone reservoirs in the study area mainly develop three types of pores: dissolution pores, residual intergranular pores, and microfractures. Residual intergranular pores are primarily controlled by early compaction processes, while dissolution processes easily form secondary pores, increasing the porosity of the reservoir. Microfractures can significantly enhance both the permeability of the reservoir. (2) Using the characteristic parameters of HPMI, the reservoir is classified into four categories, labeled as type I to type IV. As the categories progress from type I to type IV, pore-throat size decreases, porosity and permeability decrease, and reservoir properties deteriorate. The overall fractal dimension of pores decreases, while the fractal dimensions of individual pore types increase. Pore connectivity becomes more complex, and heterogeneity strengthens. (3) Reservoir porosity shows a strong positive correlation with permeability. As reservoir properties improve, the number of macropores increases, leading to a higher Reservoir Quality Index (RQI) and better oil-bearing characteristics.
孔隙结构是评价储层特征和评估油气资源潜力的关键参数。了解储层孔隙结构变化与含油性质之间的关系至关重要。通过结合薄片铸体、扫描电子显微镜（SEM）、显微计算机断层扫描（micro-CT）和高压压汞法（HPMI）等技术，我们对研究区延长组长4+5段致密砂岩储层进行了研究。该分析阐明了样品的孔隙结构与分形特征及其含油性质之间的关系。结果表明：（1）研究区致密砂岩储层主要发育三种孔隙类型：溶蚀孔隙、残余粒间孔隙和微裂缝。残余粒间孔隙主要受早期压实作用控制，而溶蚀作用易形成次生孔隙，增加储层孔隙度。微裂缝可显著提高储层渗透率。（2）利用高压压汞法的特征参数，将储层分为四类，分别标记为I类至IV类。随着类别从I类到IV类的推进，孔隙喉道尺寸减小，孔隙度和渗透率降低，储层性质变差。孔隙的整体分形维数减小，而单个孔隙类型的分形维数增加。孔隙连通性变得更加复杂，非均质性增强。（3）储层孔隙度与渗透率呈强正相关。随着储层性质的改善，大孔隙数量增加，导致储层质量指数（RQI）更高，含油特征更好。
