Abstract
An amount of oil remains in oil reservoirs even at the high water-cut stage of produced liquid from oil wells. To reveal the mechanism of displacement rates to affect the remaining oil in pore scales, a two-dimensional (2D) glass etching pore network model and real-time visual system were set up to observe the characteristics of oil distribution from water flooding and study the influence of displacement rates on oil recovery. It was found that the geometry of remaining oil in the pore network is diverse and dynamically changed at the high water-cut stage. Three geometric representative parameters were defined for the classification of five types of remaining oil (contiguous, branching, film, dropwise, bar columnar type), and controlling mechanisms for each type of remaining oil were analyzed. The experimental results show that the remaining oil saturation decreases from 21.2% to 6.5% when water injection rates increase from 0.05 to 0.5 mL/min. The increase in displacement rate improves the displacement efficiency of four types of remaining oil in the range of 55.00% to 93.67% except for dropwise type. The experimental data also indicate that the reduction in continuous residual oil and branched residual oil mainly contributes to the improvement of oil recovery of the whole network model. With the increase in displacement rate (from 0.05 to 0.1, 0.2, 0.3, 0.4, and 0.5 mL/min), the areas of five types of representative local residual oil reduce step by step. This research validates that the increase in water flooding rate in porous media leads to reduction in oil saturation, and it will improve oil recovery in oil reservoirs by enhancing water injection rates.
Highlights
With the development of oilfield water flooding, most oilfields have entered the middle–high water-cut stage
The experimental data indicate that the reduction in continuous residual oil and branched residual oil mainly contributes to the improvement of oil recovery of the whole network model
This research validates that the increase in water flooding rate in porous media leads to reduction in oil saturation, and it will improve oil recovery in oil reservoirs by enhancing water injection rates
Summary
With the development of oilfield water flooding, most oilfields have entered the middle–high water-cut stage. Ryazanov et al [28,29] used different Berea sandstone samples scanned by CT to extract a three-dimensional pore network structure for displacement simulation They quantitatively analyzed the relationship between residual oil saturation and average contact angle. The glass etching model and micro image real-time acquisition system were used to observe the characteristics of oil–water two-phase seepage in the process of micro water displacement, explore the influence of oil displacement speed on the micro displacement efficiency of different forms of remaining oil, and quantitatively analyze the influence of different displacement speed on the distribution of different types of remaining oil in high water-cut stage, which provides a reference and basis for further tapping the potential of remaining oil
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