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The main purpose of this investigation is to study the dynamic characteristics of shut-in and restart process in reservoirs with high water cut and strong vertical heterogeneity. The physical model, which includes three layers with low, medium, and high-permeability from top to bottom, was made according to the similarity law. Water drive test, the first restart test, and the second restart test were conducted, respectively. Water cut, oil recovery, and saturation distribution of the remaining oil were obtained during the tests. On this basis, mechanisms of shut-in and restart process of the reservoir were analyzed. It is concluded that appropriate developing plan such as layering mining and cyclic waterflooding should be implemented for developing strong heterogeneity reservoirs. The shut-in and restart tests showed that closing the water-flooded layer is beneficial for enlarging the sweep volume. Besides, water cut of 98% does not mean the economic limits of waterflooding. Under the effect of capillary force and gravitational differentiation, oil and water will redistribute in the formation. The redistribution of the oil and water, the fluctuation of the pressure difference, and the rebuild of the flow path, which produce parts of the bypassed oil, are the main mechanisms of the recovery enhancement by shut-in and restart operation. It should be noted that the shut-in and restart process indeed prolongs the waterflooding development. However, simply replying on the oil and water distribution under static conditions cannot greatly enhance the oil recovery.

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Lab experiments, field pilots, and numerical modeling focusing on fluid flow aspects have indicated that multi-branch wells are technically effective and promising. Several researchers have conducted some experiments for a fishbone well strategy with mixed results. Our objective in this work is to study the impact of the different fishbone well patterns, such as branch angle, on the distribution of remaining oil after water flooding. In this paper, the interference effect between branches on oil recovery is studied in three steps. First, the interferences between fishbone wells with different branch angles were measured by hydro-electric simulation experiments. Second, two-dimensional visualization water flooding experiments were carried out to clarify the remaining oil distribution at different branch angles. Third, the distribution of oil and water in fishbone wells was verified by establishing a numerical model. The modeling results agree well with the experimental phenomena. At the same time, the variation trend of water and oil production in each branch is analyzed by numerical simulation results. The results indicate that the production is strongly dependent on the branch angles, and the highest recovery was 60.2% at a 45° branch angle.