Microscopic Characteristics of Water Flooding and the Affecting Factors of Low-Permeability Sandstone Reservoir in Zhidan Area, Ordos Basin, China

Abstract

This paper is to analyze the issues arose during water-flooding exploitation of the low-permeability sandstone reservoir in Ordos Basin, China, and to provide relevant theoretical supports. The method of sandstone micro-model for water flooding experiment was used here to simulate water flooding process, in order to analyze the characteristics of water flooding in low permeability sandstone reservoir from the microscopic view. In addition, the study explored affecting factors to displacement efficiency of low-permeability sandstone reservoir, by analytical tests of physical properties, casting thin sections observation, scanning electron microscope (SEM) and x-ray diffractometer test. The results show that the main displacement methods are homogeneous displacement, finger displacement and mesh displacement in the five experimental models, and a combination of multiple displacement methods in one model is also common. Distribution patterns of residual oil observed in the experimental models include circuitous residual oil and cut-off residual oil. The highest displacement efficiency can reach up to 55.19%, while the average is 42.41%. The displacement efficiency is relatively high, suggesting a good prospect for water-flooding development of the reservoir. We analyzed the possible affecting factors for displacement efficiency of low-permeability sandstone reservoir, from both the objective factors of reservoir and human controllable factors, including physical properties of the reservoir, heterogeneity of pore structure, wettability of the reservoir, volume of injected water and displacement pressure, etc. It turns out that heterogeneity of pore structure is the most critical factor. The greater the heterogeneity of pore structure is, the more likely the circuitous residual oil would be and then the decrease of displacement efficiency.