CO2 emission was the major cause that accounted for the global warming and climate chance. How to reduce CO2 footprint to stop or slow down the global warming has been hot topic. As a developing country, China has become the largest CO2 emission nation in the world during the industrialization process to develop economy, although the CO2 emission intensity has been reduced significantly compared to previous stage. China has promised and succeeded to keep the promise reduce carbon intensity to meet the requirement of Paris Agreement. To meet the promise to attain carbon peak emission in 2030 and carbon neutrality in 2060 (CPCN), carbon capture, utilization and storage (CCUS) is an important and necessary step. Considering the high cost, high energy intensity and complex technology integrated optimization add uncertainties of CCS, utilization of captured CO2 can be of vital importance. One of the most attractive CCUS in China is CO2 enhanced oil recovery with captured CO2 (CCS EOR). CO2 EOR with captured CO2 may be one the best CCUS ways for China for the following three reasons. First, it can meet the increasing oil demand while reducing the carbon intensive coal. Second, around 66 CO2 EOR field tests have been conducted in China and experiences have ben gained. Finally, CO2 EOR in the USA was a proven technology which can increase oil production significantly and stably. Latest CCUS technology progress in China was reviewed. As of July 2021, 49 projects were carried out or under construction. Net CO2 avoided costs from 39 projects varied from 120 to 730 CNY/ ton CO2 (18.5-112.3 USD/ ton CO2). Although CCUS technology development in China was significant, the gap between global leading levels are obvious. Current challenges of CCS EOR include high CO2 capture cost, small scale, low incremental oil recovery, long-time huge capital input. The costs can be significantly reduced when the scale was enlarged to a commercial scale and transportation costs were further reduced by either pipelines or trains. CO2 transportation with well-distributed high-speed rail in China may be a feasible choice in future. If the CO2 EOR in China develops with the same speed as the USA, CO2 used for EOR in 2050 can be as high as 87.27 million tons. CO2 used for CO2 EOR in 2050 can account for 17% to 44% of the CO2 emission. CCS EOR in China will provid both domestic and international companies with good opportunities.

Polymer flooding is drawing lots of attention because of the technical maturity in some reservoirs. The first commercial polymer flooding in China was performed in the Daqing oilfield and is one of the largest applications in the world. Some laboratory tests from Daqing researchers in China showed that the viscoelasticity of high molecular weight polymers plays a significant role in increasing displacement efficiency. Hence, encouraged by the conventional field applications and new findings on the viscoelasticity effect of polymers on residual oil saturation (ROS), some high-concentration high-molecular-weight (HCHMW) polymer-flooding field tests have been conducted. Although some field tests were well-documented, subsequent progress was seldom reported. It was recently reported that HCHMW has a limited application in Daqing, which does not agree with observations from laboratory core flooding and early field tests. However, the cause of this discrepancy is unclear. Thus, a systematic summary of polymer-flooding mechanisms and field tests in China is necessary. This paper explained why HCHMW is not widely used when considering new understandings of polymer-flooding mechanisms. Different opinions on the viscoelasticity effect of polymers on ROS reduction were critically reviewed. Other mechanisms of polymer flooding, such as wettability change and gravity stability effect, were discussed with regard to widely reported laboratory tests, which were explained in terms of the viscoelasticity effects of polymers on ROS. Recent findings from Chinese field tests were also summarized. Salt-resistance polymers (SRPs) with good economic performance using produced water to prepare polymer solutions were very economically and environmentally promising. Notable progress in SRP flooding and new amphiphilic polymer field tests in China were summarized, and lessons learned were given. Formation blockage, represented by high injection pressure and produced productivity ability, was reported in several oil fields due to misunderstanding of polymers' injectivity. Although the influence of viscoelastic polymers on reservoir conditions is unknown, the injection of very viscous polymers to displace medium-to-high viscosity oils is not recommended. This is especially important for old wells that could cause damage. This paper clarified misleading notions on polymer-flooding implementations based on theory and practices in China.

Polymer flooding is one of the most promising chemical enhanced oil recovery (EOR) techniques which have both high incremental oil recovery factor (IORF), low cost and wide reservoir applicability. The first field test of polymer flooding was reported in the United States. The first commercial polymer flooding in China started in Daqing oilfield, which has been remained the largest application in the world. However, encouraged by the conventional field applications and new findings of polymer's viscoelasticity effect on residual oil saturation, some high concentration high molecular weight polymer flooding (HCHMw) field tests have been conducted and reported. Although some field tests were documented, subsequent progress was seldom reported. According to a review of latest polymer flooding projects in China, it is found that HCHMw have only very limited application in Daqing. This is not in agreement with the expectations especially that viscoelastivity of synthetic partically hydrolyzed polyacrylamide (HPAM) is drawing much attention recently. This paper explains why HCHMw is not widely used at present. Different opinions on polymer's viscoelasticity effect on ROS reduction are also critically reviewed. Other field progress of salt-tolerance polymer flooding tests and new amphiphilic polymer tests in Daqing were well Associative polymer (APs) commercial application and some new polymers used in China were also introduced. Risk of high polymer injection pressure, optimum viscosity ratio, blocking mechanism, and capillary number theory are discussed. Learning from many polymer flooding field applications has been given. In the end, quaternary recovery in post-polymer flooding reservoirs practices are compared. This paper helps to clarify some misleading ideas in polymer flooding implementations based on theory and practices of polymer flooding in China.

CO2 flooding, a promising technique of enhanced oil recovery, is widely used for its capability of boosting oil recovery, and reducing greenhouse gas emissions. In this study, the oil displacement performance of supercritical CO2 is tested in laboratory under immiscible flooding. The results show that: Supercritical CO2 improves oil recovery, by virtue of its low viscosity, high diffusivity, and easy dissolution. With the same pore volume (PV), supercritical CO2 flooding significantly boosted the oil recovery factor. The factor reached the maximum, when almost 1.5PV of CO2 was injected. As CO2 moved from the gas phase to the supercritical state, the oil displacement efficiency increased by 10%. To obtain the same oil recovery factor, non-supercritical flooding needed to inject more CO2 than supercritical flooding. Light hydrocarbon components (C1-7) in crude oil were gradually extracted before CO2 breakthrough, while heavy hydrocarbon components (C7+) were extracted mainly after CO2 breakthrough. In addition, supercritical CO2 flooding extracted more intermediate hydrocarbons than critical CO2 flooding. To sum up, supercritical flooding outperforms non-supercritical flooding in injection performance, oil displacement efficiency, and oil exchange rate.

Polymer flooding is very promising chemical enhanced oil recovery technique because it has been widely field tested in many oil fields and commercially applied in several countries in onshore reservoirs. The understanding of polymer flooding mechanisms is still developing, even though the principal mechanism was sweep efficiency increase due to reduced mobility ratio of water and oil due to reduced mobility of water. The incorporation of polymer flooding mechanisms and practical challenges make some projects fail to attain economical or technical goal. For offshore reservoirs, the polymer flooding becomes more difficult because of limited space and harsh reservoirs. Although there were hundreds of polymer flooding field tests in onshore reservoirs, polymer flooding in offshore reservoirs remains limited. In this paper, the previous onshore polymer flooding lessons and findings were briefly reviewed to look into the mechanisms which can guide the design of polymer flooding in offshore reservoirs. Then, the lessons learned from previous offshore reservoirs were reviewed. Advices were given to improve the field test performance. it is conclude that low concentration polymer solution with moderately-low viscosity should be injected into offshore reservoirs to keep displacing pressure between injectors and producers. The injected polymers should have good transportation ability which avoids the formation blockage. The optimum injection timing remains to be further investigated because the evidences. The injection rate should be controlled to avoid well casing damage which has been observed in onshore reservoirs. Except for Bohai oilfield, the formation blockage was not reported in offshore reservoirs. However, the microfracture can form in injectors which improved the injectivity of polymers as long as the injected polymers have good transportation capacity.