Analyzing the Effects of Multi-scale Pore Systems on Reservoir Properties—A Case Study on Xihu Depression, East China Sea Shelf Basin, China

Abstract: Determining the distribution and properties of multi-scale pores and the effect of these pores on reservoir properties is very significant for the analysis of the factors controlling pore structures and reservoirs quality. In this study, mercury injection porosimetry (MIP), field-emission scanning electron microscopy analysis (FE-SEM), and low-field nuclear magnetic resonance (NMR) experiments were conducted on the seven sandstone samples from Xihu Sag of the East China Sea Shelf Basin (ECSSB). The result shows that the MIP data were consistent with the other two methods so that MIP data can be used to classify pore sizes. By combining the experiment results with fractal theory, the pore size distribution can be divided into five groups: Ⅰ-micro-pores, Ⅱ-micro-pores, small pores, medium pores, and macro-pores. Considering the importance of pore throats size to the reservoir performance, the average throat based on the contribution of throats to permeability ( D ¯ ) was determined and taken as average pore throat size. Moreover, the proportions of these pores/pore throats were determined, and the effects of these pores/pore throats on reservoir parameters (porosity (φ), permeability (K), and irreducible/ bond water saturation (Swi)) were analyzed. The results show that medium pores (2.5 ∼ 25μm) strongly influence φ and Swi, and D ¯ is the major control on permeability. In addition, the relationships of types of pores, such as primary pores and mixed pores, to the medium pores and D ¯ were analyzed in order to clarify the impact of pore textures. The results imply that the concentration and sizes of the primary pores appear to the most important factors controlling the development of medium pores and D ¯ .