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The opening of natural fractures during water injection in fractured tight oil reservoirs can expand the swept volume of water flooding， but it also easily forms high-permeability channels. Therefore， it is crucial to understand the impact of natural fracture opening on water injection development for enhancing the effectiveness of water flooding in tight oil reservoirs. This paper presented a method that coupled the Perkins-Kern-Nordgren （PKN） model with an oil-water two-phase flow model， which utilized the embedded discrete fracture method （EDFM） to establish a numerical simulation approach of oil reservoirs for finely characterizing fracture dynamics during water flooding and compare its results with analytical solutions to verify its accuracy. The numerical simulation results indicate that the fracture propagation velocity at the well bottom exhibits a characteristic of rapid initial expansion followed by a slow-down under constant pressure water injection. The average pressure within the fracture fluctuates due to the opening and closing of fractures during water injection-induced fracture propagation. In a single-injection and single-production mode， there is a critical value for fracture propagation length； the fracture expands the swept volume of water flooding when the fracture propagation length is below the critical value. However， the fracture causes water channeling when the fracture propagation length exceeds the critical value. The proposed coupled model of fracture propagation was applied to numerical simulation studies of unstable water injection in the X low-pressure tight oil reservoir. The results suggest that unstable water injection could moderately induce fracture opening， increase the swept volume of water flooding， prevent rapid water encroachment in oil wells， and significantly improve the water flooding development effect in tight oil reservoirs.

The existing non-linear flow model does not consider the influence of temperature change on the non-linear flow law. Therefore， based on the capillary flow model， the Hagen-Poiseuille equation， and the boundary layer theory， as well as the influence of the temperature on the thickness of the boundary layer and the yield stress of the fluid， a dynamic non-linear flow model in low-permeability porous media considering the influence of temperature was derived. Then， the fitting verification was carried out according to the experimental data in published literature， and the calculated flow velocity curve and minimum start-up pressure gradient were highly consistent with the experimental data， which revealed the correctness of the dynamic non-linear flow model. Meanwhile， the comparative analysis with the static non-linear flow model and the Darcy flow model illustrated the rationality of the dynamic non-linear flow model. The sensitivity analysis of the flow velocity curve revealed that the increase in coefficients A and B made the flow velocity curve right-shift； the curvature degree of the non-linear flow section was weakened， and the minimum start-up pressure gradient was increased. The increase in the temperature had a much more significant effect on the flow velocity curve， which made the velocity curve move up obviously. The curvature degree of the non-linear flow section weakened， and the minimum start-up pressure gradient increased. The proposal of this dynamic non-linear flow model further enriches the development of the non-linear flow theory and can be extended to the numerical simulation of two-phase flow and high-temperature and high-pressure oil and gas reservoirs.

Aims: The flow of electric current in the root-soil system relates to the pathways of water and solutes, its characterization provides information on the root architecture and functioning. We developed a current source density approach with the goal of non-invasively image the current pathways in the root-soil system. Methods: A current flow is applied from the plant stem to the soil, the proposed geoelectrical approach images the resulting distribution and intensity of the electric current in the root-soil system. The numerical inversion procedure underlying the approach was tested in numerical simulations and laboratory experiments with artificial metallic roots. We validated the method using rhizotron laboratory experiments on maize and cotton plants. Results: Results from numerical and laboratory tests showed that our inversion approach was capable of imaging root-like distributions of the current source. In maize and cotton, roots acted as “leaky conductors”, resulting in successful imaging of the root crowns and negligible contribution of distal roots to the current flow. In contrast, the electrical insulating behavior of the cotton stems in dry soil supports the hypothesis that suberin layers can affect the mobility of ions and water. Conclusions: The proposed approach with rhizotrons studies provides the first direct and concurrent characterization of the root-soil current pathways and their relationship with root functioning and architecture. This approach fills a major gap toward non-destructive imaging of roots in their natural soil environment.

Dynamic fracture propagation significantly affects water flooding efficiency in tight oil reservoirs. This phenomenon, where moderate fracture openings can enhance water flooding volume and alleviate injection challenges, has been underexplored in current literature. Understanding dynamic fracture behavior poses a challenge due to the difficulty in characterizing them within traditional reservoir numerical simulators. In this study, we propose a numerical simulation method that integrates the KGD dynamic fracture model with a two-phase flow model. This approach enables detailed exploration of dynamic fracture evolution in reservoir scenarios featuring one injector and one production well. Our findings reveal that fractures extend from the water injection well to the oil production well, exhibiting rapid initial growth followed by a slower rate. Fluctuations in fracture tip pressure correspond to cycles of opening and closure. We observe that cumulative oil production increases more rapidly when injection pressure exceeds the fracture opening pressure. However, this growth rate diminishes beyond a certain threshold, highlighting the critical role of injection parameters in dynamic fracture efficacy. Optimal water flooding performance is achieved when injecting water slightly above the fracture opening pressure. Furthermore, we compare water cut curves generated by conventional commercial simulators with our fracture propagation model. Our model's water cut curve aligns better with on-site data, indicating improved historical fitting accuracy. In conclusion, our study underscores the importance of dynamic fractures in enhancing water flooding efficiency in tight oil reservoirs and presents a robust numerical simulation framework for better understanding and management of reservoir dynamics. [ABSTRACT FROM AUTHOR]