Abstract
Water injection is an effective method for developing low permeability sandstone reservoirs. In the process of water flooding, reservoir damage can occur due to clay mineral content changes and it will significantly affect oil production. There are few investigations on the changes in clay mineral content and the degree of reservoir damage after injecting the water into low permeability sandstone reservoirs with different permeabilities and lithologies. In this study, low permeability natural cores from different lithological strata were collected from 4 wells in the Daqing sandstone reservoir, and clay mineral components and contents were measured through X-ray diffraction. Changes in the clay mineral content were determined after water injection. The reservoir damage mechanism by clay mineral migration was determined by analyzing scanning electron microscopy (SEM) images after water injection. Meanwhile, the porosity and permeability of the cores were tested after water injection, and the degree of reservoir damage in different lithological strata was determined. The clay mineral content ranges from 6.78 to 14.14% in low permeability sandstone cores and declines by 49.73% after water flooding. Illite, chlorite and illite/smectite mostly decrease, and kaolinite decreases the least. Due to the large particle size of kaolinite, kaolinite migration will block the pore-throats and cause formation damage after water flooding. In argillaceous siltstone and siltstone, kaolinite particles blocking pore-throats are very serious, and the permeability decreases greatly by 21.87–36.89% after water injection. With increasing permeability, the permeability decreases greatly after water injection. The findings of this study can help to better understand the mechanisms of formation damage after injecting water into low permeability sandstone reservoirs.
Highlights
The maximum oil recovery of natural drives is only 20–60% (Zhou et al 2019), and it is much lower in low permeability reservoirs (Zheng et al 2009)
Some clay mineral particles are produced in the water and crude oils in the oil wells, and others accumulate in micropores or throats (Grude et al 2015; Stück et al 2013; An et al 2016; Meng et al 2015; Sadhukhan et al 2007)
Few studies have provided a quantitative analysis on the degree of reservoir damage after water flooding for different lithologic reservoirs, and there is limited knowledge about the damage caused by clay minerals from water injection in low permeability sandstone reservoirs
Summary
The maximum oil recovery of natural drives is only 20–60% (Zhou et al 2019), and it is much lower in low permeability reservoirs (Zheng et al 2009). Clay mineral components and contents will change due to the development of long-term water injection (Jiang et al 2012; Strand et al 2007), and they influence the microscopic porous structures and microscopic seepage characteristics in low permeability reservoirs. Few studies have examined the change in clay mineral content for reservoirs with different permeabilities. Few studies have provided a quantitative analysis on the degree of reservoir damage after water flooding for different lithologic reservoirs, and there is limited knowledge about the damage caused by clay minerals from water injection in low permeability sandstone reservoirs. It can provide insight into water injection development in low permeability sandstone reservoirs
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