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For Changqing Triassic extra-low permeability reservoirs,due to poor reservoir physical property, high filtration resistance, existing natural micro-fractures, water flooding development has great difficulty. Foam-assisted oxygen-reduced air flooding technology has distinct advantages for extra-low permeability reservoirs on improving oil recovery and it combines the advantages of foaming flooding and air flooding with low cost and obvious incremental oil effect. In the meantime, injection of oxygen-reduced air could reduce explosion risks which is significant for field implement. Recent years, based on the water flooding development, foam-assisted oxygen-reduced air foam flooding tests have been conducted. Relying on these tests, the micro-displacement mechanisms have been deepened, flooding systems have been developed for extra-low permeability high salinity reservoirs, and the matching injection-production parameter optimization technologies and safety monitoring and controlling system have been formed, the explosion limits and oxygen reduction limits have been determined, an overall technological process which is integrated and effective covering from the injection to the production has been established, and obvious effect has been obtained. The main purpose of this paper is to summarize achievements and knowledge of researches and tests and form a technical system, which has crucial significance to the further promotion in extra-low permeability reservoirs of Changqing oilfield, and also provides a certain degree of references for the development of similar reservoirs in the world.

The CO2 flooding technology has achieved successful applications and results in marine sedimentary low porosity and permeability reservoirs in the USA. It not only complements producing energy quickly and brings high oil displacement but also avoids the poor water injectivity. For continental sedimentary extra-low permeability reservoirs (0.1–1 mD) of Ordos Basin in China, the lithology changes rapidly and pore structure is complex, the formation fluids composition change greatly after advanced water injection and volume fracturing [1, 2]. Therefore, in the process of CO2 flooding in these reservoirs, the interaction among CO2 and rocks and formation fluids will change the reservoir physical properties and then affect the ultimate recovery [4]. In this paper, a series of experiments of the CO2-rock interactions and CO2-fluid interactions were conducted to investigate the dissolution and scaling mechanisms of CO2 under the reservoir conditions, corresponding numerical simulations had been done to evaluate the effect of the CO2 dissolution and scaling on ultimate oil recovery. The results show that temperature, pressure difference and scaling ions content have a great impact on the formation of inorganic salt precipitates. The higher the temperature, the less the precipitate; the greater the pressure difference, the more the precipitate; the higher the scaling ions content, the more the precipitate; precipitation and dissolution occur simultaneously, it demonstrates that the improvement of reservoir physical properties by dissolution is greater than the damage of inorganic precipitation to reservoir physical properties. The experimental results show that the porosity, permeability and pressure are all exponential relations, which can be used to establish the exponential characterization method of porosity and permeability change rate after CO2 formation water rock interaction. Based on the above analysis, the dissolution plays a dominant role in the process of CO2 flooding in ultra-low permeability reservoirs, which is the main factor affecting the rock porosity and permeability [5]. This experiment has guiding significance for the study of CO2 flooding mechanism and EOR in similar reservoirs.

The Jurassic low permeability reservoir in Changqing Maling has entered the stage of middle and high water cut production after long-term water injection development. In order to improve the reservoir development effect and further explore a new way to enhance oil recovery of Jurassic reservoir, the significant development test and study of polymer-surfactant binary flooding were carry out in Maling BS area in 2011.

Jurassic reservoirs in Ordos Basin are typical low permeability reservoirs, most of them have entered high water cut and high recovery percent stage, therefore it is difficult for conventional measures to increase oil recovery. The polymer surface binary flooding technology can effectively improve the ultimate recovery rate of this kind of reservoir. Based on the well microstructure, reservoir status, remaining oil distribution and dynamic data analysis in the test area, this paper summarizes the fine injection-production adjustment technology of binary flooding suitable for low permeability reservoir. It is concluded that the key factors to improve oil recovery in low permeability reservoirs are the continuous injection system, the unblocked near-well-bore zone, the reasonable pressure maintenance level and the relative homogeneity of reservoirs. After the implementation of binary flooding in Changqing Jurassic reservoir, the resistance of underground fluid seepage increased, and the formation of some oil Wells was blocked, and the liquid production of oil wells cannot be recovered. Therefore, it is necessary to cooperate with the stimulation measures and injection-production adjustment to increase the liquid production. In order to effectively improve oil recovery in low permeability reservoirs, the polymer surface binary system must be combined with fine injection-production adjustment technology. According to these study results, differentiated production well adjustments had been carried out, and the field test results were significant.

Due to poor physical properties, high percolation resistance and natural micro fractures, the primary water flooding recovery of Changqing oilfield extra-low permeability reservoirs is only 20.3%. Especially when the reservoir enters the rapid water cut increase development stage, the oil production rate is greatly reduced, and it is difficult to produce the remaining oil by using conventional technology. Surfactant flooding has good injection performance, and the combination of surfactant flooding and profile control technology can effectively improve the displacement efficiency while enlarging the sweep volume. There are differences in micro flooding mechanism between surfactant flooding and conventional water flooding in ultra-low permeability reservoir. In this paper, the inspection well cores of Changqing extra low permeability reservoirs were selected to make a real sandstone model, and the micro displacement characteristics of surfactant flooding have been studied. The results show that: 1. The percolation characteristics of water driving oil in pores during surfactant flooding are mainly uniform displacement. 2. Surfactant flooding is mainly used to strip oil through emulsification. For the small pores that the displacement fluid can’t enter, the residual oil can’t be displaced, and the ability to improve the sweep efficiency is limited. 3. Compared to water flooding, surfactant flooding has higher displacement efficiency, which can increase the displacement efficiency by 2.86–14.29%, which is 50–70%. The residual oil of the model after surfactant flooding can’t enter is 22–35%.

Changqing oilfield Jurassic reservoirs are characterized by low permeability, high formation water salinity and high content of calcium and magnesium ions. For surfactant-polymer binary flooding, indoor experiments have been conducted to research the viscosity of SP solutions with high salinity water, the interfacial tension and the effect of injection volumes and injection methods on oil displacement efficiencies. The polymer which is suitable for low permeability and high salinity formations has been selected, the surfactant with good performance and compatibility and low cost has been optimized. Established binary systems and injection parameters provide the basis for numerical simulations and surface process designs. The experiment results show that the selecting suitable SP system has the viscosity of over 18 mPa s, which meets the requirement under the Jurassic reservoirs condition; oil-water interfacial tension maintains 10−3 mN/m after five times of static adsorptions; the improved oil displacement efficiency of core flooding experiments is greater than 15%; through the combination of surfactants and polymers with different molecular weights, SP system can be injected effectively and plug the large pores without plugging formation.

Low-permeability low-pressure fractured reservoirs in Ordos Basin have low water flooding recovery factors, while CO2 core flooding experiments are limited, the visualization of CO2 flooding physical simulation experiment still being in the blank state, CO2 flooding visualised experiments have been conduct by using specialized ultra-low permeability sandstone microcosmic models to observe flow characteristics of CO2 flooding. The experiment results indicate that: ① in the process of CO2 flooding under the supercritical pressure condition, gas–oil interface disappears in the front end, rear-end CO2 is in supercritical state, which enable CO2 to enter into smaller throats and to displace oil thoroughly; ② direct CO2 flooding has better displacement efficiency which is 10% higher than that of CO2 flooding after water flooding; ③ CO2 flooding after water flooding still can improve oil displacement about 10%; ④ CO2 flooding can improve both microscopic displacement efficiencies and macroscopic displacement efficiencies, and formation microscopic pore structure and heterogeneity are important factors which affect the CO2 flooding efficiencies.

Recent evidence indicates that E2F1 transcription factor have pivotal roles in the regulation of cellular processes, and is found to be dysregulated in a variety of cancers. Long non-coding RNAs (lncRNAs) are also reported to exert important effect on tumorigenesis. E2F1 is aberrantly expressed in gastric cancer (GC), and biology functions of E2F1 in GC are controversial. The biological characteristics of E2F1 and correlation between E2F1 and lncRNAs in GC remain to be found. In this study, integrated analysis revealed that E2F1 expression was significantly increased in GC cases and its expression was positively correlated with the poor pathologic stage, large tumor size and poor prognosis. Forced E2F1 expression promotes proliferation, whereas loss of E2F1 function decreased cell proliferation by blocking of cell cycle in GC cells. Mechanistic analyses indicated that E2F1 accelerates GC growth partly through induces TINCR transcription. TINCR could bind to STAU1 (staufen1) protein, and influence CDKN2B mRNA stability and expression, thereby affecting the proliferation of GC cells. Together, our findings suggest that E2F1/TINCR/STAU1/CDKN2B signaling axis contributes to the oncogenic potential of GC and may constitute a potential therapeutic target in this disease.

Changqing old oilfield Jurassic reservoir's average calibration recovery is 24.7%, with geological reserves recovery of 16.6%, water cut of 65.2%. And most of Jurassic reservoirs are in the middle and later field life, part of them has entered the high water cut and high recovery stage. Traditional water flooding way for improving oil recovery becomes more difficult, and new method has to be considered. Maling oilfield BS district is a typical representative, with high water cut of 90.8%, high recovery percent of 26.1% and low oil recovery rate of 0.25%. To explore the new way to improve oil recovery, the polymer and surfactant (SP for short) important pilot test has been developed. The low permeability reservoir indoor core data in high water cut stage and inspection well results indicate that the reservoir permeability, pore combination characteristics and pore type changed greatly after long-term water flooding development. These changes bring more difficulties to the continue development, especially the high injection pressure, which can cause other problems for well pattern infilling and EOR. This paper takes the high injection pressure problem of Maling BS district Jurassic reservoir for example, analyzes the physical property change law on the following aspects: the development mode in the past, core analysis, formation sensitivity, interstitial matter, well test interpretation results, in order to help to further effective development and provide important parameters for tertiary oil recovery technique for similar reservoirs and others.