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This study takes the tight sandstone of the lower sub‐member of the first member of the Eocene Shahejie Formation (Es1x) in the Suning area, Raoyang Sag, Bohai Bay Basin. Furthermore, it determines the rock type of the middle‐deep tight sandstone through lithologic profiling, core observation and log data analysis. The genetic control factors of tight sandstone in the study area are analysed using conventional thin section, pore‐casted thin section and scanning electron microscope, and the characteristics and genetic control factors of tight sandstone reservoirs are summarized. The research results show that the tight sandstones in this area are primarily feldspathic sandstone and feldspathic lithic sandstone, with high quartz contents, around 61.50%. The average porosity of the reservoir in the study area is 4.69%, and the average permeability is 2.92 mD, which are characteristics of low‐porosity and low‐permeability reservoirs. Through research, it has been found that the distribution of sedimentary facies and diagenesis in the study area control the development and distribution of 'sweet spots'. Both compaction and cementation reduce the physical properties of the reservoir, while dissolution can increase porosity, thereby increasing the physical properties of the reservoir; dissolution resulted in an increase of approximately 3.57%–3.69% in the porosity of the tight reservoir in the study area, with an average porosity increase of 3.63%, and is the main controlling factor for the development of 'sweet spots' in the reservoir. The results provide an important basis for guiding the exploration and development of tight sandstone oil and gas in the lower sub‐member of the first member of the Eocene Shahejie Formation (Es1x)in the Suning area. [ABSTRACT FROM AUTHOR]

Most of buried hill reservoirs are in the late stage of water flooding development, especially for this kind of reservoir with large water-oil volume ratio, it is more difficult to develop the residual oil in matrix system. This article presents a new idea about technical policy of extraction depressurization development which has not been studied in domestic and abroad, and analyses the major influence factor of liquid extraction depressurization by dual-media numerical simulation in depth. The results show that it can increase the oil production in matrix system to a greater extent by liquid extraction depressurization. The liquid extraction capacity is the most important factor which contains the effect of uniform speed liquid extraction, variable speed liquid extraction and periodic liquid extraction. Under the condition of keeping stable production, the larger the liquid volume extracted, the faster pressure dropped, and the more oil will be discharged in matrix system. According to these results, this paper suggests the reasonable technical policy of liquid extraction depressurization, and it is of great significance to obtain good effect of slowing down water cut and enhancing oil recovery in depressurization development of the buried hill reservoirs with high water cut and enough energy.

High-saturated reservoir is characterized by high saturation pressure and high gas-oil ratio. The effects of water flooding are easily influenced by the formation pressure and GOR, especially at the late stage. This article presents the relationship between the reasonable pressure maintenance level and GOR as well as water cut based on the actual characteristics of high-saturated reservoir. Then, the reservoir numerical simulation method is used to analyse the influence of pressure recovery rate and water cut rise under different injection-production ratios and injection-production methods. Research results show that the pressure maintenance level of high-saturated reservoir is larger than normal reservoirs. Bigger injection-production ratio results in not only faster pressure recovery rate but also higher water cut. Cyclic injection and production method under the maximum injection rate and liquid extraction amount can enhance oil recovery rate and control water cut rise at the same time, which plays a significant role in improving the development effect of water-flooding in high-saturated reservoirs at the late stage.