BackgroundCoronavirus disease 2019 (COVID-19) pandemic has become the most severe global health issue. Abnormal liver functions are frequently reported in these patients. However, liver function abnormality was often overlooked during COVID-19 treatment, and data regarding liver functions after cure of COVID-19 is limited. This study aimed to reveal the changes of liver function tests (LFTs) during hospitalization, and its clinical significance in patients with COVID-19.MethodsIn this retrospective, bi-center study, a total of 158 hospitalized patients diagnosed with COVID-19 in China were included from January 22nd, 2020 to February 20th, 2020. Clinical features, laboratory parameters including LFTs, and treatment data were collected and analyzed. LFTs included alanine transaminase, aspartate aminotransferase, alkaline phosphatase, gamma-glutamyl transferase, and total bilirubin. Patients were considered with abnormal LFTs when any value of these tests was higher than upper limit of normal.ResultsOf 158 patients with COVID-19, 67 (42.41%) patients had abnormal LFTs on admission and another 50 (31.65%) patients developed abnormal LFTs during hospitalization. The incidence of LFTs abnormality in severe COVID-19 cases was significantly higher than non-severe cases. All LFTs in COVID-19 patients were correlated with oxygenation index. There was no statistical difference in treatment between the patients with or without liver test abnormalities. By the time of discharge, there were still 64 (40.50%) patients with abnormal LFTs. Logistic regression analysis identified younger age, hypertension and low lymphocyte counts as independent risk factors for persistent abnormal LFTs during hospitalization.ConclusionLiver function tests abnormality was common in COVID-19 patients and was more prevalent in severe cases than in non-severe cases. A substantial percentage of patients still had abnormal LFTs by the time of discharge.

During the development of low permeability oil reservoirs in Changqing oilfield, the nonuniformity of injection profile is a commonly seen problem. Conventional profile control methods face the difficulty caused by hard injection and poor reservoir adaptability. Polymer microspheres (PMs) are considered to have good profile control capabilities due to their properties such as hydration swelling and plugging. Therefore, it is proposed to use PMs profile control method to improve the oil recovery in low permeability reservoirs. There are two key factors for the success of PMs profile control, which are matching relationship and plugging properties. In this paper, the average pore throat diameter of the pilot test area was calculated, and the hydration swelling properties were studied by measuring the diameter of PMs. The plugging properties of PMs were studied by displacement experiment. Based on the experimental research, in 2016, 4 well groups in Changqing oilfield were selected for PMs profile control. Calculation results showed that average pore throat diameter of the study area was 2.28μm. The diameter of 800 nm named PCE been selected for PMs profile control. The hydration swelling experiment results showed that PCE initial average diameter was 784nm. After 13 days of hydration swelling, PCE average diameter was 2798 nm and increased by 2.57 times. The results of PCE displacement experiment showed that resistance factor, blocking rate and retention rate was 3.5, 71.42% and 96.22%, respectively. The performance of the PCE application in oilfield showed that 11 production wells were effective after PCE injection, and the success rate of profile control was 47.8%. The average validity period was 150 days. And a total of 1365.5t of oil had been increased during the validity period. For the injection wells, the average injection pressure and the thickness of water absorbing layers increased by 1.415MPa and 3.28m respectively.

For low-permeability sandstone reservoirs, CO 2 huff and puff is an effective method for increasing oil recovery. Commonly, sandstone formations with low permeability have diverse pore and throat sizes and a complex pore-throat structure, which essentially affects the flow characteristics of CO 2 and oil in the formation and further the CO 2 huff and puff performance. It is necessary to understand the recovery degree of various microscale pore sizes under different operational parameters during CO 2 huff and puff in tight sandstones. In this work, several experiments of cyclic CO 2 injection are conducted with sandstone core samples with low permeability. Before and after the injection, the T 2 spectra of the sandstone cores are compared using the NMR technique. We then discuss the micro residual oil distribution and recovery degree in different pores, such as micropores (<1 ms), small pores (1−10 ms), medium pores (10−100 ms), and macropores (>100 ms). It is found that the recovery degree in the different pores increases as the pore size increases. Oil can be recovered more easily from macropores and medium pores during the cyclic CO 2 injection. The oil contained in micropores is relatively difficult to extract considering a high capillary force under immiscible conditions. It is found that the total recovery degree increases with the increase in soaking time. However, such a recovery degree increment in small pores is not as large as that achieved in medium and large pores. With the CO 2 injection volume increase, the total recovery degree increases. When the CO 2 injection volume is less than 1.5 PV, it is challenging to extract the oil from micropores and small pores. As the cycle number increases, the cyclic oil recovery decreases, and most of the oil is produced in the first cycle. This suggests that under the experimental conditions of this study, the cycle number of CO 2 huff and puff shall not be more than 3. This work is important to further understand the CO 2 huff and puff process for improving oil recovery in sandstone reservoirs with low permeability.

Much research has been carried out on nanoscale polymer microspheres (PMs) in laboratories in recent years. However, there are limited reports on the practical application of nanoscale PMs in ultralow permeability reservoirs. This paper reports a field application case of nanoscale PMs for in-depth profile control in the ultralow permeability oil reservoir. In the paper, the characteristics of the reservoir and the problems faced during development are analyzed in detail. Then, the PMs with calibration diameters of 300 nm and 800 nm are researched by evaluation experiments, and are selected for in-depth profile control in the ultralow permeability oil reservoir. Finally, according to the effect of the pilot application, the performance of PMs is evaluated, and a more suitable size for the pilot test reservoir is determined. The experiment's results show that the PMs have a good capacity for swelling and plugging. For the PMs with a calibration diameter of 300 nm, the final equilibrium swelling ratio is 56.2 nm·nm −1 , and the maximum resistance coefficient and the blocking rate after swelling are 3.7 and 70.31%, respectively. For the PMs with a calibration diameter of 800 nm, the final equilibrium swelling ratio is 49.4 nm·nm −1 , and the maximum resistance coefficient the blocking rate after swelling are 3.5 and 71.42%, respectively. The performance evaluation results show that nanoscale PMs can be used for in-depth profile control in the ultralow permeability oil reservoir. After the application of PMs in the pilot test area, the average water cut decreased by 10.4%, the average liquid production of single well-increased by 0.9 t/d, and the average thickness of the water-absorbing layer increased by 1.77 m. Comparing the dynamic data variation of well-groups using the PMs with the calibration diameter as 800 nm and the calibration diameter as 300 nm, it indicates that, for the pilot test area, PMs with a calibration diameter of 300 nm are more suitable than PMs with a calibration diameter of 800 nm.

Polymer microsphere (PM) profile control has been attributed to improving sweep efficiency during the oil development process. The critical factors for PM conformance control are the plugging properties controlled by matching the relationship between the throat diameter and particle size and the injection parameters. A new matching relationship between the reservoir and PM based on the function of blocking rate and the ratio of throat diameter to microsphere diameter (C R) is established to choose the most appropriate PM size. The blocking rate indicates that it will get the most excellent plugging effect when C R is 0.5. The displacement experiments under different injection concentrations and other injection volumes show that the blocking rate is increased by injection concentration and finally stabilized. A similar trend is presented between the injection volume and plugging rate. The optimal injection concentration is 0.5%, and the optimal injection volume is 0.3 PV. According to the new size selection method and injection parameter optimal method, PM100 chooses to conduct field application. PM100 presents a good performance with a success rate of 37.5% and a validity period of more than 120 days, and its daily oil production rate increased 1.7 times, on average, and finally, the total oil increase is 556 t. The optimal size microsphere shows a good EOR effect, which indicates that this size selection method is reasonable.