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CO2 flooding technology is an effective technical means to enhance the recovery of low permeability reservoirs. After CO2 comes into contact with crude oil， the asphaltene in the system is deposited in a solid form， which causes a certain blockage to the reservoir， but the dissolution improves the flow capacity of the reservoir as a whole at the same time. The damage of CO2 flooding to low permeability reservoirs under different injection methods is different. The organic scale plugging mechanism， reservoir wettability， and CO2-water solution corrosion evaluation experiments were carried out after continuous CO2 injection and CO2-water alternating injection. The variation characteristics of relative permeability curve parameters were evaluated， and the damage of different injection methods of CO2 flooding to low permeability reservoirs was quantitatively characterized. The results show that the organic scale produced by CO2 flooding would block the pore throat of the rock， but on the whole， the dissolution caused by the reaction of CO2 and chlorite is stronger， which makes the recovery of the low permeability reservoirs effectively enhanced. Moreover， the organic scale blockage caused by CO2-water alternating injection is weaker than that caused by continuous CO2 injection， and the dissolution effect is better. The permeability loss rate is lower. It could achieve a better oil displacement effect in pores with a radius of more than 0.2 μm and increase the pore space and flow channel of the rock so that the recovery of low permeability reservoir could be effectively improved.

In terms of the collaborative optimization of CO2 flooding for Enhanced Oil Recovery (EOR) and CO2 sequestration, previous studies have co-optimized both cumulative oil production and CO2 sequestration by various algorithms. However, these solutions fail to optimize the CO2 injection schemes for high-water cut oil reservoirs. This paper presents an optimization methodology for CO2 flooding and sequestration in high-water cut oil reservoirs. The production optimization was carried out by adjusting the injection and production rate. To solve the proposed objective functions, the simultaneous perturbation stochastic approximation (SPSA) algorithm is applied in this paper, and the CMG-GEM module is utilized to simulate the reservoir production performance. A typical high-water cut reservoir in the Shengli oilfield was used to verify the feasibility of the presented methodology. In this paper, the production performance and net present value (NPV) for continuous gas injection under different water cuts were analyzed. The optimal timing of transforming from water flooding to gas displacement for the high-water cut reservoir was optimized. In addition, the optimal water–gas ratios for Water-Alternating-Gas (WAG) flooding were determined. The sensitivity of NPV to gas injection price and carbon subsidy was analyzed. The results show that when the gas price is 0.178 $/m3 and the carbon subsidy is 0.0169 $/m3, the optimal timing of transforming from water flooding to gas injection should be earlier than the time when the water cut is 0.82. Through the combination of NPV, cumulative oil production rate, and CO2 sequestration volume for WAG flooding, the optimal WAG ratio should be 1:2. The presented method in this paper considers various economic indicators and can optimize CO2 flooding and sequestration in high-water cut oil reservoirs efficiently, which can provide some guidance for the design of CO2 flooding schemes in high-water cut oil reservoirs. [ABSTRACT FROM AUTHOR]

Owing to the prevalent viscosity in the subsurface medium, seismic waves experience amplitude attenuation effects during their propagation in visco-acoustic media. Therefore, it is crucial to develop a method that can compensate for wavelet amplitude attenuation and enhance imaging quality. In this paper, we derive an expression for corrected ray complex travel time by introducing the quality factor Q. Additionally, we modify the classical Gaussian beam propagation operator to an adaptive focus type propagation operator. Our research presents an adaptive focused beam migration imaging method specifically designed for viscous acoustic media, incorporating a combination of traditional Gaussian beam migration imaging methods. In comparison to traditional migration methods, the proposed approach achieves energy focusing along the phase axis and significantly improves imaging quality. The validity and effectiveness of our method are confirmed through the obtained imaging results. [ABSTRACT FROM AUTHOR]

CO2 flooding technology is an effective technical means for tertiary oil recovery in high water cut reservoirs. Using an existing well pattern to inject CO2 is an economical and feasible development method under low contemporary oil prices. Although the particle migration caused during the displacement process will block the pore throat of the rock, the injection of CO2 can effectively reduce the CO2 injection pressure, and the dissolution that occurs during the injection process improves the seepage capacity of the fluid as a whole. In this study, assessments of particle migration and plugging after CO2 flooding and evaluations of rock dissolution by CO2-aqueous solution were carried out, and the variation characteristics of the relative permeability curve before and after displacement were evaluated, further explaining the influence of CO2 flooding on reservoir seepage capacity. The results show that, in the process of CO2 injection, the injection pressure decreases under different injection rates. After CO2 flooding under oil conditions, the core permeability loss was 43.8%, and after cleaning with toluene and anhydrous ethanol, the core permeability recovery was 24.3%, indicating that the particles were bound by crude oil during the migration process and accumulated into clusters, resulting in blockages. Although there was a certain degree of blockage, the CO2-aqueous solution mainly reacted with chlorite and released Ca2+, Mg2+, and Fe2+ ions. The concentration of Ca2+ increased by 157.43%, the concentration of Mg2+ decreased by 43.33%, and the concentration of Fe2+ decreased by 50.47%, indicating that, although the generated MgCO3 and Fe2O3 blocked the pore throat of the rock, the overall dissolution effect of CO2 on CaCO3 was stronger, and the overall seepage capacity of the fluid was improved. To a certain extent, this technique can improve the water injection capacity and the effect of subsequent water flooding. [ABSTRACT FROM AUTHOR]

Objective: The outbreak of coronavirus disease (COVID‐19) coincided with the season of influenza A pneumonia, a common respiratory infectious disease. Therefore, this study compared ultrasonography and computed tomography (CT) for the diagnosis of the two diseases. Methods: Patients with COVID‐19 or influenza A infection hospitalized at our hospital were included. The patients were examined by ultrasonography every day. The CT examination results within 1 day before and after the day of the highest ultrasonography score were selected as the controls. The similarities and differences between the ultrasonography and CT results in the two groups were compared. Results: There was no difference between the ultrasonography and CT scores (P =.307) for COVID‐19, while there was a difference between ultrasonography and CT scores for influenza A pneumonia (P =.024). The ultrasonography score for COVID‐19 was higher than that for influenza A pneumonia (P =.000), but there was no difference between the CT scores (P =.830). For both diseases, there was no difference in ultrasonography and CT scores between the left and right lungs; there were differences between the CT scores of the upper and middle lobes, as well as between the upper and lower lobes of the lungs; however, there was no difference between the lower and middle lobes of the lungs. Conclusion: Ultrasonography is equivalent to the gold standard CT for diagnosing and monitoring the progression of COVID‐19. Because of its convenience, ultrasonography has important application value. Furthermore, the diagnostic value of ultrasonography for COVID‐19 is higher than that for influenza A pneumonia. [ABSTRACT FROM AUTHOR]