Abstract
In this paper, the variation of clay minerals and their influence on reservoir physical properties and residual oil before and after ASP flooding are analyzed. The results show that the total amount of clay minerals in reservoirs decreases after ASP flooding in the ultra-high-water-cut-stage reservoirs of the Naner Zone in the Saertu Oilfield, Songliao Basin. Therein, the illite content reduces, while the content of illite smectite mixed-layer and chlorite increases. The content of kaolinite varies greatly. The content of kaolinite decreases in some samples, while it increases in other samples. The clay minerals block the pore throat after ASP flooding. As a result, the pore structure coefficient and the seepage tortuosity increase, the primary intergranular pore throat shrinks, and the pore–throat coordination number decreases. Nevertheless, the dissolution of clay minerals reduces the pore–throat ratio and increases porosity and permeability. The variation of clay minerals after ASP flooding not only intensifies the reservoir heterogeneity but also affects the formation and distribution of residual oil. The residual oil of the oil–clay mixed adsorption state is a newly formed residual oil type related to clay, which accounts for 44.2% of the total residual oil reserves, so it is the main occurrence form of the oil in reservoirs after ASP flooding. Therefore, the exploitation of this type of residual oil has great significance to enhance the oil recovery in ultra-high-water-cut-stage reservoirs.
Highlights
ASP flooding refers to a chemical flooding method that utilizes a composite system of alkali, surfactant, and polymer for petroleum exploitation
The results of this study provide technical support for the effective development of residual oil after ASP flooding
Scanning electron microscopy (SEM) and X-ray diffraction methods were applied to the surface morphology, and wholerock mineral and clay mineral analysis of the core samples was conducted to determine the pore structure and mineral composition of the cores and to explore the characteristics of changes in the pore structure and clay minerals of the cores before and after ASP flooding (Fang, et al, 2016; Zhu et al, 2021)
Summary
ASP flooding refers to a chemical flooding method that utilizes a composite system of alkali, surfactant, and polymer for petroleum exploitation. Reservoirs change under the chemical dissolution of rock minerals and the precipitation and agglomeration of clay mineral particles in the pore fluid because of the adsorptionflocculation of the polymer (Kazempour et al, 2013; Huang et al, 2020) All these changes of the pore structure and physical properties of reservoirs will affect the formation and distribution of residual oil (Liu et al, 2013; Liu et al, 2014; Liu et al, 2015; Mansa et al, 2017; Wu et al, 2015b). It is significant for the effective development of residual oil to investigate the variation of clay minerals after ASP flooding in ultra-high-water-cut-stage reservoirs. The results of this study provide technical support for the effective development of residual oil after ASP flooding
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