Abstract

Carbon Capture, Utilization, and Storage is a greenhouse gas emission reduction . To achieve a win-win target of improving oil recovery and carbon sequestration through gas injection, Huabei Oilfield has conducted carbon dioxide-enhanced oil recovery and carbon sequestration pilot tests in the Balixi Buried Mountain Oil Reservoir. With a increase in gas injection wells, CO2 was detected in Dongying Formation and Shahejie Formation of the upper strata of the buried mountain in new drilled wells. A carbon isotope investigation was conducted on those wells to further clarify the source of CO2 and evaluate the effectiveness of the buried mountain closure,. Based on this investigation, an novel method evaluating the CO2 storage and injection capacities of the heterogeneous carbonate reservoirs in Balixi Buried Mountain was established. A total of 4000 sampling points of 3 wells are used to establish the new model. From the results, it was clarified that the isotope in the active sections of CO2 gas measurement is lighter in the Dongying Formation of Balixi Buried Mountain. Meanwhile, the composition in those sections is dry, showing the characteristics of mainly biogenic gas. In contrast, the carbon isotope of the active sections of CO2 gas measurement is heavier in the Shahejie Formation had a heavier carbon isotope weight and higher Meanwhile, the composition in those sections is humidity, showing the characteristics of thermogenic gas. Therefore, CO2 in the Dongying Formation and Shahejie Formation of the upper strata of Balixi Buried Mountain is self-generated in the strata, further confirming the effective closure of the buried mountain.

Abstract

The traditional alcoholamine CO2 capture method requires a desorption temperature of 120 °C, which is energy-intensive and costly; the study of a CO2 capture method with low energy consumption and low cost is the key to realising the CCUS. In this paper, based on the alcoholamine chemical absorption method of CO2, N-methyldiethanolamine (MDEA) solution was used as the CO2 capture absorbent, and its desorption performance was compared between the traditional heating and the electric field-assisted action, so as to investigate the enhancement effect of the electric field-assisted action on the rich-liquid regeneration and desorption of the alcoholamine absorbent under different conditions. The optimum reaction conditions and the maximum desorption rate of the electric field-assisted desorption were explored by changing the experimental factors such as voltage and temperature. The results showed that at the desorption temperature of 105 °C, the desorption rate of conventional heating was only 55.18%; when the desorption temperature was still 105 °C but with the addition of 4.5 V voltage assistance, the desorption rate could reach 97.92%; It has better cyclic regeneration performance, with a 1% decrease in CO2 desorption after 5 cycles. By comprehensively comparing the desorption performance of organic amine desorption of CO2 under the conditions of traditional heating and electric field-assisted heating, it can be seen that the appropriate low-voltage electric field has a promotional effect on the desorption of CO2 from alcoholamine solution, and the development of this technology is of great significance to effectively improve the regeneration efficiency of carbon capture absorbents and reduce the energy consumption in the process of CO2 desorption.

Abstract

In recent years, AI technology has been used to evaluate carbon sequestration reservoirs and caprocks, but the black-box nature of neural networks raises credibility concerns. This study employs the Kolmogorov-Arnold Network (KAN) to interpretably characterize carbon sequestration caprocks, including lithology identification and porosity prediction. Inspired by the Kolmogorov-Arnold representation theorem, KANs feature learnable activation functions on edges and univariate spline functions, enhancing both accuracy and interpretability. Smaller KANs achieve accuracy comparable to larger MLPs in data fitting and solving partial differential equations. For lithology identification, well log datasets from the Daniudi and Hangjinqi Gas Fields were used, with a KAN achieving a test accuracy of 0.806, surpassing traditional MLPs. For porosity prediction, datasets from the Gulf of Mexico wells were used, with a KAN achieving an MSE of 0.055. Fine-tuning and retraining derived a physical formula representing porosity based on well log data, elucidating the relationship between porosity and various parameters. This study demonstrates that KANs provide accurate and interpretable predictions, offering promising prospects for carbon sequestration site selection and reservoir characterization, thereby enhancing model credibility and advancing AI applications in geological sciences.

Abstract

CO2 flooding is an effective way to improve recovery factor and achieve CO2 storage. In the late stage of oilfield waterflooding, due to the long-term erosion of injected water, the geological parameters of the reservoir have changed significantly compared with the initial stage, which has a great impact on the distribution of remaining oil. In the conventional reservoir numerical simulation, the changes of reservoir seepage parameters, physical parameters and fluid-related properties over time are not considered, which leads to the fact that the results of the reservoir numerical model are not conform with the actual oilfield development situation and affect the subsequent CO2 flooding effect. Aiming at the problem that the effect of CO2 flooding is not clear after waterflooding in oil reservoir, by using the T-Navigator numerical simulation software, the variation of permeability was characterized by the displacing water multiple. Considering the blockage of suspended solid, oil droplets in different water quality, established a time-varying permeability method for reservoir damage caused by different water quality. Study the influence and reservoir time-varying characteristics of different water quality after waterflooding on enhanced oil recovery by CO2 flooding. The results indicate that: (1) Different water quality in waterflooding can make an impact on CO2 flooding. When the core is damaged by poor water quality, the porosity and permeability decreases. (2) After waterflooding, the average recovery factor by CO2 flooding reduces by 4.54%, the average formation pressure of the injection well increases by 4.56%, the injection capacity declines, the remaining oil saturation rises, and the CO2 spread range decreases. This conclusion is beneficial to selecting appropriate blocks suitable for CO2 injection, and provides a reference for the research on enhancing oil recovery by CO2 flooding after waterflooding in low-permeability reservoirs.

Abstract

Sandy conglomerate reservoirs are known for their tight and highly heterogeneous nature. CO2-WAG (Water-Alternating-Gas) has been identified an effective method to enhance oil recovery of such reservoirs, while also achieving a certain amount of CO2 storage. However, the enhanced oil recovery (EOR) mechanisms and the main controlling factors of this technology remain unclear, posing challenges in providing clear guidance for field practices.
In this paper, the CO2-WAG displacement experiments were conducted using cores from different layers in parallel to simulate a heterogeneous reservoir and address these challenges. Nuclear Magnetic Resonance (NMR) technology was used to monitor the dynamic distribution of residual oil during the displacement process. This approach explored the EOR mechanisms of CO2-WAG across multiple scales, including the reservoir, layer, and pore levels. Additionally, the influence of water-gas ratio and injection rates on the oil recovery at multiple scales were investigated.
The experimental results show that the overall recovery factor of CO2-WAG flooding reaches about 24%, representing a 41.18% increase compared to pure CO2 flooding. Analysis of residual oil changes in different layers and pore types reveals that CO2-WAG flooding effectively inhibited early breakthrough in high-permeability layers, improved displacement efficiency in medium and low-permeability layers, and enhanced micro-displacement efficiency in medium and small pores. Moreover, the study demonstrates that increasing the water-gas ratio gradually enhances the oil recovery, primarily attributed to increased oil recovery in low-permeability layers and micropores. However, as the injection rate gradually increases, the overall oil recovery progressively decreases. This is attributed to higher injection rates resulting in earlier gas breakthrough in high-permeability layers, thereby hindering CO2 sweep through the medium- and low-permeability layers. Conversely, the increase in displacement pressure resulting from high injection rate leads to enhanced oil recovery in the micropores.

Abstract

At present, CO2 is one of the main media for gas injection to enhance oil recovery in low permeability reservoirs with good mining application. The development of complex fault block reservoirs has problems such as strong non-homogeneity, difficult injection, low production, etc. In this paper, we carried out a study on the mechanism of WAG flooding to improve the recovery rate in complex fault block reservoirs. Firstly, using 2D profile experiments, it is clarified that gravity overlap and the expansion of swept volume in WAG flooding are the main mechanisms for production increase. Secondly, phase fitting is carried out by combining the field geological data and production data to provide a fluid model for the subsequent numerical simulation study. Finally, the reservoir development method as well as the injection and recovery parameters are studied separately based on the injection and recovery well network model. The simulation results show that the current gas injection pressure can realize the miscible flooding, and the WAG flooding schedule has strong adaptability. The influence of parameter was analyzed through a single factor sensitivity analysis to obtain the optimal injection and extraction parameters. Among them, the well spacing is the main factor affecting the WAG flooding. The results of this study have an important guiding role for the design of CO2 flooding in complex fault block reservoirs.

Abstract

Carbon dioxide (CO2) is typically transported in liquid or supercritical states, which are highly corrosive, posing a risk of corrosion leakage in transport pipelines. The function of detection technologies lies in the ability to promptly identify pipeline leaks, thus reducing potential risks.
This study includes an experimental investigation into the acoustical technology for pipeline leak detection based on Distributed Acoustic Sensing (DAS). The experiments were carried out within a 210-meter-long pipeline with an inner diameter of 44 millimeters, equipped with electromagnetic valves and circulation pumps. In this experiment, designed to validate the feasibility of the detection technique, pipeline leakage detection with supercritical carbon dioxide was performed.
It was validated through detection experiments involving different phases and leak severities that the feasibility of pipeline leak detection technology based on DAS is established. The distinguishing properties of acoustic signals between leak and normal states were explored using the spectrum subtraction algorithm (SSA) and correlation analysis approaches to compare the DAS signals. The results indicate that significant signal intensity differences exist in specific frequency domains for pipeline leak signals. Signals remain reasonably constant during steady operation because flow rates are consistent. When a leak occurs, large changes in signals near the leak location are noted, allowing leak identification based on differences in signal response times. During continuous leakage, the energy of signals at specific frequencies around the leak site is significantly higher than in areas without leaks.
This study may provide novel methodologies for low signal-to-noise ratio processing and bad point signal identification in the DAS signals, and establish a theoretical foundation for the engineering application of DAS in CO2 pipeline leak detection.

Abstract

It is important to improve CO2 miscible flooding efficiency by using additives for CO2 enhanced oil recovery (EOR). To bridge the gap, this study aims to investigate the effect of pentanol additives on the Minimum Miscibility Pressure (MMP) of CO2-oil systems under reservoir conditions.
Molecular dynamics (MD) simulations were conducted in this work by using LAMMPS software to model the interactions between CO2, crude oil, and pentanol molecules under reservoir conditions. The force field parameters were carefully calibrated and validated against experimental data. The vanishing interface method was employed to determine the MMP by observing changes in the gas-liquid interface and assessing miscibility under different conditions. The impact of pentanol concentration (0-10 wt%) on MMP was thoroughly analyzed.
The simulation results reveal that pentanol significantly reduces the MMP of CO2-oil systems. The MMP decreases as the concentration of pentanol increases, reaching an optimal point before leveling off. In addition, CO2 molecules preferentially cluster around the hydroxyl groups of pentanol, enhancing their interaction with the oil phase and facilitating the disruption of oil molecular cohesion. This interaction effectively reduces the MMP, demonstrating pentanol’s potential as a powerful additive for CO2 miscible flooding.
The findings provide valuable insights for optimizing the processes of CO2 enhanced oil recovery and storage, offering a practical approach for achieving carbon neutrality through improved reservoir exploitation techniques.

Abstract

The oil reservoir in the peripheral oil fields of northern Songliao Basin is characterized by low permeability and complex structures. With the decreasing oil production, there is an urgent need to change the injection and production methods. Laboratory experiments is performed in order to study the application of CO2 displacement technology. The results of laboratory experimental studies shows that CO2 injection can significantly increase the fluidity of crude oil through dissolution, viscosity reduction, and gas-injection expansion. It indicates that CO2 has good dissolution, viscosity reduction, and gas injection expansion effects, which can significantly increase the fluidity of crude oil. Based on the characteristics of the reservoir, it is believed that the low-permeability reservoir around northern Songliao Basin is suitable for CO2 flooding. CO2/water alternating injection increases oil recovery by 28.13 percentage points compared to water flooding.Production parameters are optimized by numerical simulation, the results show that the higher the level of formation pressure recovery, the better CO2 flooding effect. The optimization result is to use a gas to water ratio of 3:1, with a water gas alternation cycle of 2 months of water injection and 2 months of gas injection.This method can increase oil recovery by 11 percentage points compared to water flooding,utilizing remaining oil effectively. The research has reference significance for CO2 immiscible flooding in other low-permeability reservoirs.

Abstract

Photovoltaic (PV) systems are being increasingly adopted in buildings, but the installed capacity often fails to account for uncertainties during the usage phase. A novel probabilistic optimization model based on the reliability level is applied to size the PV arrays on a residential building. The minimum total installation area of the PV panels is treated as the objective of the optimization. To consider the impacts of various uncertainties during the installation and continuous operations of PV system, a design variable, installation angle, and multiple environmental variables, including annual solar irradiation, ambient temperature, and attenuation rate on the system efficiency, are integrated into the model. A unique statistic profile of uncertainty is established for each of the variables based on the verifications from the documented literature. In the meantime, to concurrently ensure the sufficient electricity supply provided by the PV system and mitigating the system degradation, constraints on the total power generation, self-use power ratio, and temperature increase were formulated. By establishing different levels of confidential reliability and magnitudes of uncertainties associated with design and random variables, the optimized size and installed angle of PV exhibited significantly different results.