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Nanotechnology applications in geothermal energy systems: Advances, challenges and opportunities
Get PDFGeothermal energy offers a sustainable solution to meet growing energy needs while mitigating environmental concerns associated with conventional fossil fuel sources. Meanwhile, nanotechnology presents innovative solutions to enhance the performance of renewable energy systems. However, its specific applications in geothermal energy are a dynamic field and have not been systematically reviewed. This paper presents an overview of the latest advancements in utilizing nanotechnology to enhance geothermal energy systems. The essential role of nanotechnology is examined across the entire life-cycle of geothermal development and utilization, encompassing various aspects including geothermal well construction, geothermal reservoir characterization, scaling and corrosion prevention, and resource recovery. The results suggest that nanotechnology holds significant promise for improving the efficiency, longevity, and profitability of geothermal energy systems. Further more, this paper outlines the potential challenges associated with nanotechnology adoption in technical, environmental, and economic terms, and offers strategies for mitigating them. Finally, the paper discusses some future perspectives on how nanotechnology can further advance geothermal energy, contributing to the global transition to a clean and renewable energy future.Document Type: Current minireviewCited as: Meng, B., Yan, G., He, P., Zhou, Q., Xu, W., Qian, Y. Nanotechnology applications in geothermal energy systems: Advances, challenges and opportunities. Advances in Geo-Energy Research, 2025, 15(2): 172-180. https://doi.org/10.46690/ager.2025.02.0
Pore-scale microfluidic investigation of unsaturated CO₂ bubble morphology and interface evolution during drainage-imbibition cycles
Get PDFCO₂ sequestration into saline aquifers can significantly reduce atmospheric greenhouse gas concentrations, making it a key geological carbon storage technology for mitigating climate change and achieving carbon neutrality targets. However, current research predominantly focuses on reservoir saturation states, with limited understanding of dynamic mechanisms at the gas-liquid interface. In this study, microfluidic experiments were conducted at ambient temperature to investigate CO₂ drainage and imbibition under varying capillary numbers, incorporating the remobilization process driven by gas-water interphase mass transfer. Collectively, these three processes determine the temporal distribution of CO₂ and water phase saturations within the porous medium, thereby influencing the efficiency and long-term stability of CO₂ sequestration. With the increase of the capillary number, the sweep efficiency of CO₂ during drainage showed an upward trend, increasing to 54.71%. Moreover, this study provides an in-depth analysis of the distribution and morphological evolution of CO₂ under conditions where the aqueous phase is unsaturated. Results indicate that the asynchronous contraction of cluster interfaces results in a heterogeneous and dynamic dissolution process; the gas-water interface evolution of double-pore ganglia resembles the brine snap-off process; and singlet structures undergo shrinkage and deformation during the dissolution process. These findings elucidate the complex interactions between CO₂-water in porous media and underscore the critical roles of capillary forces and interfacial dynamics in geological carbon sequestration.Document Type: Original articleCited as: Xue, R., Chang, Y., Wang, S., Wang, P., Sun, H., Liu, H., Lv, P. Pore-scale microfluidic investigation of unsaturated CO₂ bubble morphology and interface evolution during drainage-imbibition cycles. Capillarity, 2025, 15(3): 74-86. https://doi.org/10.46690/capi.2025.06.0
Numerical simulation of power-law acid flow in rough fractures of carbonate rocks
Get PDFAcid fracturing is the most widely applied technology for stimulating carbonate reservoirs. Meanwhile, the effectiveness of this method largely depends on factors such as acid penetration distance, fracture morphology and conductivity, all of which are closely governed by acid flow behavior. A wealth of numerical simulations have been conducted to characterize acid flow during fracturing, whereas the coupled effects of acid rheological properties and fracture surface roughness on the acid flow behavior remain underexplored. In this work, a three-dimensional numerical model of acid etching fracture was developed by coupling an acid-rock reaction model with computational fluid dynamics methods, which comprehensively incorporates the rheological property of acid and fracture surface roughness. Validation against experimental data showed a deviation of 11.15% in dissolved mass, with errors within 10.00% for most roughness parameters, confirming the numerical model’s accuracy. Furthermore, the numerical model was employed to investigate the quantitative effect of the rheological index on acid transport and the spatiotemporal evolution of acid flow and dissolution. The results revealed significant interdependencies among flow velocity, shear rate, acid-rock reaction rate, and fracture width, all of which evolve dynamically over time and space. Moreover, it was found that the non-uniform distribution of flow velocity, shear rate, acid-rock reaction rate is caused by fracture surface roughness, and the degree of non-uniformity is enhanced as the shear-thinning capacity of the acid increases. This work provides a robust numerical framework for the simulation of the transport and reaction of acids with power-law characteristics in three-dimensional rough fractures, thus offers valuable theoretical insights for guiding the optimization of acid fracturing parameters and enhancing reservoir stimulation efficiency.Document Type: Original articleCited as: Liu, X., Li, Q., Chen, W., Li, N., Huang, Y., Li, H. Numerical simulation of power-law acid flow in rough fractures of carbonate rocks. Advances in Geo-Energy Research, 2025, 17(3): 226-240. https://doi.org/10.46690/ager.2025.09.0
A method for enhancing well-log resolution of thin lithological heterogeneities using wavelet transform and automated machine learning
Get PDFClastic reservoirs exhibit complex and diverse lithologies. Some lithological heterogeneities, occurring as thin but effectively low-permeability units, have pronounced impact on CO2 flooding schemes and oil recovery. Thin low-permeability units within permeable sandbodies typically exhibit weak well-log responses, and are therefore of difficult recognition using conventional well-log analysis methods. To address this challenge, a hierarchical method is proposed for interpreting thin lithological heterogeneities by integrating wavelet transform and machine learning. The discrete wavelet transform enhances well-log responses of thin heterogeneities. An automated machine-learning framework is designed, which integrates multiple algorithms and achieves automated parameter optimization. This machine-learning method is then applied to well logs to establish a nonlinear mapping model between lithology and well-log responses. Additionally, the hierarchical nature of the workflow highlights lithological contrasts, facilitating a more accurate lithological differentiation by dividing the recognition of thin heterogeneities into three levels. Benefiting from these three advantages, the proposed method offers potential to significantly enhance the accuracy of well-log interpretations. The results demonstrate that this method yields accurate identification of lithological units as thin as 0.2 m for muddy beds and 0.3 m for diagenetic units, achieving a recognition accuracy exceeding the conventional well-log interpretations. This method also shows significant potential for broader applications, including the identification of other types of geological entities of limited thickness, and determination of reservoir parameters at fine scales.Document Type: Original articleCited as: Li, W., Liu, L., Yue, D., Gao, J., Zhang, S., Colombera, L. A method for enhancing well-log resolution of thin lithological heterogeneities using wavelet transform and automated machine learning. Advances in Geo-Energy Research, 2025, 17(2): 149-161. https://doi.org/10.46690/ager.2025.08.0
Prediction of proppant accumulation morphology in coal reservoir fractures using numerical simulation and response surface approach methodology
Get PDFProppants are widely employed in coalbed methane extraction. The use of proppant effectively mitigates the closure of hydro-fractures during production, thereby maintaining efficient gas flow pathways. The transport distance and accumulation morphology of proppants within hydro-fractures are critical factors influencing coalbed methane production; however, their quantitative and comprehensive evaluation remains insufficiently explored in coal reservoirs. In this study, a Box-Behnken design was adopted to establish a four-factor, four-level experimental framework for investigating the influence of multiple variables on dune parameters within secondary hydro-fractures through a coupled computational fluid dynamics-discrete element method approach. Response surface methodology and statistical significance testing were employed to quantify the effects of multiple parameters and to establish an empirical predictive model of proppant dune characteristics. The adequacy and significance of the proposed model were verified through analysis of variance. The results demonstrated that both the transport distance and accumulation morphology of proppant within hydro-fractures are jointly controlled by the coupled influence of multiple parameters. Four basic variables, including injection rate, proppant size, proppant density and sand carrying fluid viscosity, were selected, and their influences on sand dune parameters were ranked. The model predictions revealed that dune height may reach up to 79.7% of the hydro-fracture height, while the horizontal dune length can extend up to 15 times the hydro-fracture height. These findings elucidate the mechanisms governing proppant transport and deposition under diverse conditions, offering valuable insights and optimization strategies for proppant selection and injection parameter design in hydraulic fracturing in coalbed methane reservoirs.Document Type: Original articleCited as: Zhu, X., Liu, W., Wei, Y., Zhou, P., Wang, Y. Prediction of proppant accumulation morphology in coal reservoir fractures using numerical simulation and response surface approach methodology. Advances in Geo-Energy Research, 2025, 18(3): 218-230. https://doi.org/10.46690/ager.2025.12.0
Nanomechanics and pore structure evolution in organic-rich shale reservoirs during high-temperature treatment: A multi-scale analysis of microscopic stability
Get PDFTo address the challenges of conflicting macroscopic mechanical tests and the inability to reveal complex nanoscale mechanisms during deep shale thermal modification, this study comprehensively investigates the microstructural and nanomechanical evolution of Longmaxi shale under heat treatment. This involves the innovative combination of gas adsorption, atomic force microscope high-resolution mapping, and multi-level spatial statistical analysis to systematically elucidate the spatial evolution of the pore structure of shale, surface morphology, and nanomechanical properties. The findings reveal a unique hardening-softening-rehardening three-stage pattern: From 25-400 ◦C, the average reduced modulus increases due to dehydration; from 400-600 ◦C, organic matter pyrolysis significantly decreases the modulus, with intense atomic force microscope topographic uplift; from 600-900 ◦C, the modulus slightly increases again due to structural collapse and pore network regeneration. Local indicators of spatial association analysis shows that this macro evolution stems from synergistic microscopic phase space reshaping. Crucially, the mesopore volume increases most significantly in the 400-500 ◦C range, and it exhibits its most notable increase. Considering energy efficiency and feasibility, this study demonstrates for the first time that 400-500 ◦C is an ideal temperature window for effective organic matter pyrolysis and nanopore optimization from a nanoscale spatial distribution and geometric stability perspective. This work provides crucial micromechanical mechanism support and precise temperature guidance for deep shale thermal modification, significantly outperforming the temperature ranges from traditional macroscopic experiments and filling the gap in macro-nanoscale mechanical discrepancies and spatial feature analysis.Document Type: Original articleCited as: Chen, Q., Tang, X., Shi, Y., Zhang, R., Shang, F. Nanomechanics and pore structure evolution in organic-rich shale reservoirs during high-temperature treatment: A multi-scale analysis of microscopic stability. Advances in Geo-Energy Research, 2025, 17(3): 241-255. https://doi.org/10.46690/ager.2025.09.0
Spontaneous imbibition of quasi-linear viscoelastic fluids
Get PDFSpontaneous imbibition phenomena are commonly observed in capillaries and porous media. The extraction of energy resources, lubrication in the machinery industry, and therapeutic applications in life sciences often involve the imbibition of complex viscoelastic non-Newtonian fluids. Although the imbibition of Newtonian fluids or simple linear Maxwell viscoelastic fluids have been well studied, investigations on the imbibition of quasi-linear or nonlinear viscoelastic fluids are still rare. This paper focuses on the imbibition mechanism of quasilinear viscoelastic fluids. Primarily, the theoretical relationship between the imbibition height and time for quasi-linear fluid in a single capillary tube is derived, by incorporating the elastic stress into the classical Lucas-Washburn imbibition theory for Newtonian fluids. Then, glass capillary imbibition experiments are performed to validate the theoretical predictions, showing good agreements. Moreover, the impacts of key viscoelastic features on the imbibition of fluids are investigated, including the viscosity ratio and the relaxation time. The results show that under the capillary dominated conditions, the imbibition rate increases with the viscosity ratio, and this trend is more pronounced at larger relaxation time. In addition, the study finds a critical Deborah number , under which the viscoelastic effect is negligible. Conversely, when the viscoelasticity is strong, the imbibition height and velocity of fluids decrease with increasing relaxation time in a nonlinear manner. The study provides important theoretical support and guidance for engineering problems involving capillary action of viscoelastic fluids, advancing the understanding of the imbibition mechanisms of non-Newtonian fluids.Document Type: Original articleCited as: Sun, S., Wang, G., Zhu, S., Dong, R., Fu, Q., Xie, C. Spontaneous imbibition of quasi-linear viscoelastic fluids. Capillarity, 2025, 17(2): 68-76. https://doi.org/10.46690/capi.2025.11.0
Design and evaluation of in-situ temperature-preserved deep rock coring systems based on analytic hierarchy process
Get PDFThe in-situ temperature preservation coring of deep rocks is crucial for studying the physical properties of cores under temperature and pressure sensitivity and for assessing resource reserves. Existing core sampling strategies in this field rarely consider temperature preservation, with most employing passive insulation structures based on vacuum technology. In this context, the main challenge is that current insulation technologies and methods cannot meet the requirements of extreme deep environments, necessitating innovative designs of deep in-situ insulation coring systems. The insulation system proposed in this paper integrates three subsystems, active insulation, passive insulation, and control system. The analytic hierarchy process is used to perform parametric analysis on the design of these subsystems. By combining heat transfer theory analysis with laboratory pre-research experiments, the evaluation index parameters in the analytic hierarchy process method are quantitatively assigned. This approach further integrates the experience and knowledge of engineering designers to obtain a comprehensive evaluation table of the design parameters. On the basis of the permutation and combination mathematical method, a full matrix set of all feasible conceptual design schemes is established, or the optimal solution is sought through scheme integration, coupling, decoupling, and optimization. The analytic hierarchy process analysis method, which combines theory and pre-experiments, provides a set of parametric analysis methods for conceptual design schemes of insulation coring systems. Furthermore, the optimization of conceptual design schemes through full matrix scheme combinations offers guidance for future data-driven optimization of multisubsystem conceptual scheme.Document Type: Original articleCited as: Chen, L., Qin, B., Li, Y., Yang, X. Design and evaluation of in-situ temperature-preserved deep rock coring systems based on analytic hierarchy process. Advances in Geo-Energy Research, 2025, 16(1): 8-20. https://doi.org/10.46690/ager.2025.04.0
Data-driven interpretable machine learning for prediction of porosity and permeability of tight sandstone reservoir
Get PDFPorosity and permeability are crucial indicators in the identification of high-quality reservoirs and favorable “sweet spot” zones, as well as key parameters when predicting and evaluating the development potential of fossil fuels like oil and gas. However, it is impracticable to collect enough core samples on vertical and horizontal planes for analysis due to the associated time and cost demand. Machine learning algorithms have shown remarkable capabilities in predicting the petrophysical properties by capturing non-linear relationships among logging data. In this study, to quantify the selection of logging curves and reduce the redundant logging data input, a novel and interpretable Permutation Importance-Set algorithm is proposed on the basis of logging data from the Upper Triassic Xujiahe Formation in the Sichuan Basin. The results indicate that, because of compaction, burial depth is the primary feature affecting the physical properties of tight sandstone reservoirs. Acoustic and spontaneous potential logs are critical for porosity, while density and spontaneous potential logs are pivotal for permeability, reflecting the complex diagenesis caused by the widespread sand-mud interbedding. Basin-level prediction models for porosity and permeability were developed using ten machine learning algorithms, then ablation studies confirmed the effectiveness of our feature selection and the reduced model complexity and over-fitting. This study offers a concise, interpretable prediction model with superior accuracy and interpretability for tight sandstone reservoirs.Document Type: Original articleCited as: Cao, L., Jiang, F., Chen, Z., Gao, Y., Huo, L., Chen, D. Data-driven interpretable machine learning for prediction of porosity and permeability of tight sandstone reservoir. Advances in Geo-Energy Research, 2025, 16(1): 21-35. https://doi.org/10.46690/ager.2025.04.0
Novel structural design and anti-erosion performance evaluation of check valve applied to deep in-situ pressure-preserved coring
Get PDFThe pressure relief check valve plays a pivotal role in determining the oil and gas content during deep in-situ pressure-preserved coring. Prolonged exposure to high-pressure, high solid-content fluids in deep wells can lead to mechanical erosion of the check valve, potentially causing severe failure and a loss of sealing integrity. To withstand the typical f low conditions in shale gas wells and on the basis of an in-depth understanding of deep f luid dynamics, a check valve was designed to operate at 70 MPa pressure and relieve pressure after coring. To mitigate erosion, a coupled Computational Fluid Dynamics Discrete Element Method model was applied to simulate fluid flow dynamics and identify regions susceptible to erosion and wear in the valve body. The findings confirmed that the proposed check valve design meets the requirements for shale gas pressure-preserved coring and testing, with erosion mainly occurring in the constricted regions of the flow path. The erosion depth was found to increase with higher inlet flow rate and mass flow rates, demonstrating a sixfold increase as the inlet flow rate rises from 10 to 30 m/s. Non-spherical particles caused significantly more erosion than spherical ones, while the erosion depth decreased with larger particle sizes, showing a 33% reduction as particle size increased from 0.02 to 0.14 mm. To avoid sealing failures caused by prolonged erosion, the constricted flow channel was redesigned to accommodate an arc-shaped structure and appropriately widened. Simulations indicated that this structure can reduce peak pressure to 69% of the original value and minimize wall impacts. The maximum erosion depth decreased by 10%, indicating the improved durability and sealing of the redesigned check valve. These results underscore the enhanced check valve’s superior erosion resistance and sealing performance, highlighting its potential for future shale gas collection and testing and providing an effective strategy to enhance the reliability and longevity of check valves.Document Type: Original articleCited as: Fang, X., Li, C., Guo, D., Wang, D., Zhao, L., Xie, H. Novel structural design and anti-erosion performance evaluation of check valve applied to deep in-situ pressure-preserved coring. Advances in Geo-Energy Research, 2025, 15(3): 190-202. https://doi.org/10.46690/ager.2025.03.0