Wastewater treatment industry, a top ten carbon emission source, has been significantly concerned in recent years. However, unclear system boundaries and undisclosed databases make it hard to estimate the greenhouse gas (GHG) emission from the wastewater treatment industry, especially in developing countries. Quantifying the total GHG emission characteristics at national level is helpful to identify the most emitted processes and propose suitable carbon mitigation strategies. This study accurately estimated the GHG emissions from Chinaâ€™s wastewater treatment industry by a model combined with operational data integrated methods and Intergovernmental Panel on Climate Change method. Then, the spatial distribution analysis and possible influential factors of total GHG emissions were further investigated by geographic model, Pearson correlation model and principal component analysis. Results showed that the national GHG emission from the total 4,205 wastewater treatment plants (WWTPs) in China in 2017 was 34.18 Mt CO2-eq, with 64.5% emitted from the consumption of electricity and chemicals. The GHG reduction strategies need to focus on process optimization and improvement at WWTPs, especially for the energy source shift, improved aeration, and on-site N2O emission from biological treatment process. After analyzing the spatial distribution characteristics, the total emission in the eastern region was approximately four times higher than that in the western region according to the Hu Line. Gross domestic product (GDP) and the treated volume of wastewater had strong positive correlations to the total GHG emissions in most first-tier cities, while there were no significant impacts on non-first-tier cities. Additionally, the impact of wastewater treatment scale on the discharge intensity is not significant, but the impact of technology is relatively obvious.
CO2-based cyclic solvent injection (CSI) process has shown great potential in enhancing heavy oil recovery while sequestrating CO2 in heavy oil reservoirs. However, the effects of gravity on the CO2-based CSI process have not been comprehensively studied yet. In this work, five groups of CO2-based CSI experiments were implemented using the 1D sand-pack model. Gravity effects were simulated by increasing the angles of the model from 0 to 45 degrees counterclockwise. The experimental results suggest that oil recovery factor decreases with increasing cycle number in all groups. However, in the groups with higher angles, more cycles and higher recovery factors are observed since the decrease rate of oil recovery is slower with increasing cycles. As the angles of the model increase from 0 to 45 degrees, the cycle number in the CO2-based CSI process gradually increases from 5 to 13, and the recovery factor dramatically rises from 29.89% to 76.74%. Moreover, the production stage is divided into three sections: initial rapid GOR decrease section, steady production section, and high GOR section. Experiments with larger angles have a longer steady production section. The main reason for these phenomena is that higher angles bring a more significant gravity effect, which can enlarge the CO2 swept area and drive crude oil in the unswept area to flow to the producer. The experimental results show that the change in model angles does not have an obvious impact on CO2 storage. Analytical models were developed for the prediction of oil recovery considering the effect of gravity in the CO2-based CSI process. This work is the first work to quantitatively characterize the effect of gravity on the EOR potential and the CO2 storage capacity of the CO2-based CSI process. The findings and innovations in this study can provide better references for field development.
CO2-based cyclic solvent injection (CSI) process is widely applied for enhancing heavy oil recovery in petroleum industry. However, the rapid decrease in oil production after 2 or 3 cycles will be encountered in previous CO2-based CSI research due to the reduction in oil saturation near the producer. Therefore, five groups of experiments were conducted using a 1D sand-pack model to explore the EOR potential in CO2-based CSI process via polymer injection assistance to increase oil saturation around the producer. Two polymer flooding assistance modes were investigated, including injection after every cycle and injection after the cycle when oil recovery factor is less than 1%. Two slug size of polymer flooding assistance were evaluated, including volume of 1 PV and the volume of total liquid produced in the previous CO2-based CSI process. Three different concentration of polymer solution, 0ppm, 250ppm and 1000ppm, were also studied. The experimental results show that the oil recovery factor is significantly improved after polymer flooding assistance during the CO2-based CSI process. The polymer flooding assistance effectively push the remaining oil toward the producer and form an oil bank for the following CO2-based CSI section, increasing the oil saturation near the producer. The highest recovery factor (70.72%) is achieved in polymer flooding-assisted CO2-based CSI process when polymer (1000 ppm concentration) was injected after the cycle that oil recovery factor is less than 1%, and the slug size equals to the volume of total liquid produced in the previous CO2-based CSI section. The economy evaluation results show the assistance mode of conducting 1000ppm polymer flooding assistance after each cycle has the lowest material cost. Moreover, a field application of this novel technique was designed and implemented in eastern China, and a significant increase in daily oil production and decrease in water cut were achieved. In conclusion, this work innovatively combines the CO2-based CSI process with polymer flooding, and a polymer flooding-assisted CO2-based CSI technology for heavy oil reservoirs is proposed. Experimental results in both the laboratory and field reveals the excellent EOR potential and economic benefit of this novel technology for heavy oil reservoirs.
Shale gas, as a strategic supplement to conventional oil and gas resources, has become the focal point of China’s oil and gas exploration and development. CO2 huff and puff, a pivotal technique in shale gas exploitation, not only effectively enhances shale gas recovery but also aligns with the goal of carbon neutrality. The nano-scale phenomena of CO2-multi-component gas micro-mobility extensively occur during the CO2 huff and puff process in shale gas reservoirs. Under the coupled variable conditions within the pore structure, the adsorption characteristics and storage state of the gas within the pores also change. This paper uses molecular simulation methods to study the adsorption characteristics of mixed gases in synergistically deforming organic nanopores, as well as the transport mechanism of mixed gases in inorganic nanopores of shale. The research found that when CO2 has the maximum proportion, the deformation is greater than at other proportions, and the maximum deformation at different proportions all occur at 5MPa. With the increase of the initial pore diameter, the amplitude of pore deformation also increases. When gas molecules begin to move in the pores, the change in cohesive energy will provide some resistance. However, when gas molecules stably move in the pores, the resistance effect produced by the cohesive energy will relatively weaken. The pore diameter at the nano-scale will change under the influence of the water film. If this effect is ignored, it will lead to a significant deviation in the calculation results of capillary pressure.
In response to the Paris Agreement’s 2050 target for net-zero Green House Gas (GHG) emissions, the European Commission forecasts a net-negative cap in the EU Emissions Trading System (EU ETS) by 2045, mostly through carbon removal. In 2022, the EU initiated a Carbon Removal Credits (CRCs) certification framework to advance this goal. However, the effective integration of CRCs into the EU ETS still presents a significant challenge. This paper introduces CO2-Echain, a comprehensive digital framework designed to manage CRCs across full-scale Carbon Capture and Storage (CCS) processes, and to enable third-party CRCs certification within the EU ETS. To ensure effective CRCs integration, the framework focuses on vital criteria such as data integrity and security, transparency and auditability, compliance, alignment with existing infrastructure and workflow, flexibility and scalability, and operational efficiency. CO2-Echain employs an edge-to-cloud architecture, leveraging distributed edge nodes and Internet of Things (IoT) devices to supervise the entire CO2 life cycle – from capture to transport and injection. It records standard CRCs certification methodologies (once established), procedures, and results into the InterPlanetary File System (IPFS). To maintain data integrity, a private blockchain deploys Smart Contracts to manage these files. A synchronized cloud platform allows authorized third-party access to IPFS files, thereby enhancing the integration of CRCs with the EU ETS. Ultimately, CO2-Echain aims to facilitate a more robust, efficient, and effective market mechanism for carbon emissions removal.
CO2 flooding is considered as one of the most effective enhanced oil recovery (EOR) methods in low-permeability reservoirs. In our work, we studied CO2 miscible/immiscible flooding in low-permeability sandstones, using nuclear magnetic resonance (NMR) and volume of fluid (VOF) method. The experimental results indicated that the oil recovery after CO2 miscible flooding is 68.13%, which is twice as much as the one after CO2 immiscible flooding; oil in large pores is mainly displaced in the process of CO2 immiscible flooding, whereas in the case of CO2 miscible flooding, the oil comes from all kinds of pores. On the basis of VOF simulation results, it was fond that oil recovery after CO2 miscible flooding is also two times the one after CO2 immiscible flooding, which are dependent on the characteristic of CO2-oil contact. Moreover, oil recovery of CO2 miscible/immiscible flooding significantly decreased with the increase of oil viscosity. The interesting observation is that piston displacement happened at the injection part and finger displacement did at the production part during CO2 miscible flooding. In the end, we found that CO2 storage rate of miscible flooding is higher than that of immiscible flooding, and CO2 storage rate also significantly decreased with the increase of oil viscosity.
The excessive dependence and abuse of fossil energy promoted the development of clean and renewable energy. Green hydrogen, generated from the hydrogen evolution reaction (HER) of renewable energy water electrolysis, is considered as an ideal choice for future energy. However, the coupling anodic oxygen evolution reaction (OER) with high potential limits the efficiency of hydrogen production. Herein, a bifunctional Ni2P-NiSe2 heterostructure aerogel (Ni-P-Se aerogel) was constructed to boost HER and replace OER by 5-hydroxymethylfurfural oxidation reaction (HMFOR) to produce high-valued 2,5-furandicarboxylic acid (FDCA) with low operating voltage and high conversion. The NiSe2 with cubic pyrite-type crystal structure was favor for anodic reconstruction, which allowed the effective generation of activated oxygen species and further promoted HMFOR. Moreover, the coupling of Ni2P modulated the adsorption energy of OH- in HMFOR and enhanced the activity toward HER. Besides, the aerogel structure with porous network structure provides abundant active sites and mass-transfer pathways. Benefit from these advantages, the optimized Ni-P-Se aerogel exhibited high HER performance (68 mV at 10 mA·cm-2), low onset oxidation potential (1.30 V) and high Faradaic efficiency (97.4% at 1.40 V) of HMFOR. Compared to OER, the two-electrode system coupled with HMFOR had significantly increased current density at low operating voltage (102 mA·cm-2 increase at 1.50 V), proving the superiority of HMFOR as alternative anodic reaction This work offers an anticipated perspective of bifunctional electrocatalysts toward the combination of HER and organics oxidation.
CO2 flooding can improve crude oil recovery,and realize CO2 underground storage, which is an important means to increase the recovery rate in tight reservoirs. CO2-water alternating flooding,which is a method to combine the advantages of CO2 flooding and water flooding,has good applicability and is the most commonly used method in gas injection preventing channeling. However,due to the low viscosity of water medium under reservoir conditions, plugging ability for water to heterogeneous reservoirs is limited during CO2-water alternate flooding, and the oil displacement effect of CO2 flooding needs to be further improved. Therefore, a low interfacial tension small molecule tackifying system (DXZT) was constructed based on small molecule oligomeric organic active substances. When implementing alternative flooding with CO2, the DXZT has good injection performance and environmental adaptability in heterogeneous tight reservoirs, meeting the needs of improving the swept volume and oil washing efficiency of CO2 flooding. In this paper, the interfacial activity, viscosity increasing, emulsification, wettability, foam properties and reservoir environmental adaptability of the DXZT were systematically evaluated. The injectivity and preventing gas channeling effect of the CO2 and DXZT alternating flooding were investigated, and the preventing CO2 channeling mechanism of DXZT was analyzed. The results show that DXZT has good interfacial activity (≤0.02mN/m ), viscosity enhancing (2.0-15.4mPa·s), environmental adaptability of high salinity, high calcium ion and acidic CO2 ( salinity ≤ 80000mg/L, Ca2+ ≤ 15400mg/L, pH ≥3 ), oil-water emulsifica -tion, water wettability and foam performance(foam comprehensive index ≥ 15443mL·min). CO2 and DXZT alternate flooding has good injectivity for tight core (0.242mD). After water flooding in heterogeneous tight cores, CO2-DXZT alternative flooding recovery increased by 14.8% than comprehensive water flooding recovery, which was better than single CO2 flooding or DXZT flooding. With the increase of alternating drive rounds, the recovery rate of low permeability core and total comprehensive recovery rate are increasing. Which shows that DXZT has the ability to block the high permeability channel,divert CO2 to the low permeability channel,start the remaining oil,and prevent CO2 channeling in high permeability zone. The anti-gas channeling mechanism of DXZT includes: DXZT increases viscosity and has better mobility adjustment ability than water; is easy to inject high permeability channel or fracture,plug and seal these channelings, and form foam with CO2 that has entered the channel,strengthen the sealing ability to high permeability channel. That is beneficial to the subsequent CO2 divert, start the remaining oil in the low permeability channel and expand the swept volume of CO2 flooding. Thus, DXZT is a new method and technology to prevent gas channeling in CO2 flooding, which has broad application prospects in improving the recovery of CO2 flooding in heterogeneous tight oil reservoirs.
The increasing levels of CO2 in the atmosphere have prompted the development of CCUS, which faces challenges such as limited mineral trapping, reservoir capacity, and the risk of leakage. To address these challenges, this review proposes in situ mineral carbonation in basalt formations, which are characterized by rapid carbon mineralization and widespread distribution. The review explores the mineral reaction mechanism in basalt reservoirs using laboratory experiments and numerical simulations or modeling. Representative research conducted in the past ten years is emphasized to indicate better carbon mineralization conditions in basalt formations. Two field-scaled pilot projects in Wallula and Iceland are explained to provide examples for future CCUS projects. However, CCUS in basalt will only become mainstream with further technological development and policy funding.
CCUS ( Carbon Capture, Utilization and Storage ) is one of the key technologies to address global climate change. Both in China and internationally, research and development on CCUS has been on the rise in recent years. In the process of CCUS implementation, safety issues are naturally inevitable. In this paper, the knowledge graphs of CCUS safety technology are drawn based on Web of Science database with the help of CiteSpace. The analysis of the countries of publication shows that the United States and China account for most of the publications. The analysis of article co-occurrences demonstrates that CCUS technical safety research is mainly concentrated in the field of energy fuels and engineering, and the development status is obtained accordingly. The co-occurrence analysis of the subject terms yielded the most frequently used terms in this field. The results show that there is a large gap in the safety research on CCUS technology, with fewer articles published and the rigor and reliability of some articles still open to question. The research on CCUS safety technology still needs to be paid attention to, both in depth and breadth, so as to provide more stringent safety for CO2 resource utilization.