Microscopic pore structure of Chang 63 reservoir in Huaqing oilfield, Ordos Basin, China and its effect on water flooding characteristics

Abstract

Chang 6 3 reservoir in Huaqing oilfield, Ordos Basin, China is featured by strong pore structure heterogeneity, which leads to prominent Jamin effect in the water flooding, difficult development process, low productivity, and massive residual oil. Accordingly, this study aims to explore the microscopic pore structure of Chang 6 3 reservoir and investigate its influence on the water flooding efficiency, based on a series of comprehensive analyses, including physical property analysis, casting thin section observation, scanning electron microscopy measurement, high-pressure mercury injection, constant rate mercury injection, and microscopic real sandstone water flooding model. It is demonstrated that gray and gray-brown feldspathic sandstone are the main reservoir lithology in the study area, with dominant pore types of residual intergranular pores and feldspar dissolution pores. Pore throat radius is unevenly distributed, and small and micro pores take the majority. Based on the comparison of capillary pressure curve characteristics and comprehensive analysis of corresponding parameters, the pore structure of the Chang 6 3 reservoir is divided into four types, namely types I-IV. They have different reservoir spaces, and their reservoir and seepage capacities decrease in the order of types I-IV pore structures. Moreover, displacement patterns in them are also different, with the finger-like-reticular displacement as the primary. In addition, pore throat radius and distribution play a critical role in the water flooding. It is also demonstrated that the water flooding efficiency increases with permeability and porosity, pore structure quality, and pore throat distribution evenness.

An Experimental Study on Stress Sensitivity of Tight Sandstones with Different Microfractures

“…Among them, the Chang 8 reservoir tight sandstone type is dominated by feldspar lithic sandstone and lithic feldspar sandstone and contains a small amount of feldspar sandstone. e lithology of the Chang 9 reservoir is dominated by lithic feldspar sandstone, followed by feldspar sandstone and feldspar lithic sandstone [30]. A total of 14 cores were selected for this study, including 5 cores in the Chang 9 reservoir and 9 cores in the Chang 8 reservoir.…”

Effect of Micropore Structure on Macroscopic Water Cut Changing Law in Strongly Heterogeneous Reservoirs

“…By combining micropore structure and other geological characteristics, the reservoir rock type can be defined [25][26][27], which could be applied to constructing a fine geological model. Micropore structure also can be used to characterize areal heterogeneity and vertical heterogeneity [28] and then further to predict interwell reservoir properties [24,29], define the remaining oil distribution and morphology, explore its influence on the water flooding efficiency qualitatively [30,31], and predict core scale drainage efficiency for different micropore structures. Other scholars [32][33][34][35][36][37] attempt to evaluate the impact of micropore structure on oil production potential, recovery factor, and dynamic performance from the point of micropore structure's influence on macrooilfield development rules.…”