Geoenergy Science and Engineering最新文献

{"title":"Significant reduction of the viscosity of waxy model oils by DC electric field","authors":"Hao Wang,&nbsp;Yingda Lu","doi":"10.1016/j.geoen.2025.213905","DOIUrl":"10.1016/j.geoen.2025.213905","url":null,"abstract":"<div><div>Wax crystallization at low temperatures greatly increases the viscosity of waxy oils and poses flow assurance challenges to their pipeline transportation. The conventional methods of lowering the viscosity of waxy oils, such as adding chemicals or externally heating the pipeline, are carbon-intensive and sometimes ineffective. Electrical treatment has emerged as a promising and low-carbon method to improve the cold flowability of waxy crude oils. While previous studies primarily focused on crude oil systems and highlighted the critical role of charged particles such as resins and asphaltenes in electrical treatment, this study systematically investigated the electrorheological behavior of model waxy oils composed solely of mineral oil and paraffin wax, without such charged particles. Using a rheometer equipped with an Electro-Rheology accessory, we characterized the changes in the oil's viscosity under DC electrical fields ranging from 0 to ±3 kV/mm. Significant viscosity reductions of up to 89 % were achieved. The viscosity reduction also strongly depended on the field direction, and negative electric fields generally result in higher reduction than those achieved by positive electric fields under the same field strength. Direct visualization by a high-resolution camera indicated that the migration of wax crystals toward electrodes is mainly responsible for the observed viscosity reduction, providing direct experimental evidence of the mechanisms supporting the negative electrorheology of waxy oils. This research greatly advances the mechanistic understanding of the interactions between wax crystals and electric fields, expanding the potential application of electrical treatments for flow assurance in pipelines.</div></div>","PeriodicalId":100578,"journal":{"name":"Geoenergy Science and Engineering","volume":"251 ","pages":"Article 213905"},"PeriodicalIF":0.0,"publicationDate":"2025-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143842526","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Modeling of multiphase fluids flow in anisotropic rock mass during CO2 sequestration in fractured reservoirs","authors":"Ngambua Ngambua Rene ,&nbsp;Weiguo Liang ,&nbsp;Yuedu Chen ,&nbsp;Shouya Wu ,&nbsp;Tresphord Chishimba","doi":"10.1016/j.geoen.2025.213904","DOIUrl":"10.1016/j.geoen.2025.213904","url":null,"abstract":"<div><div>Understanding multiphase flow in fractured rock is essential for optimizing CO₂ storage in natural reservoirs. This study presents a model for CO₂ and water flow in fractured coal, examining the effects of injection pressure, reservoir conditions, and fracture characteristics on storage efficiency. Results indicate that connected fractures enhance fluid transfer, while isolated fractures retain less CO₂. The rock matrix exhibits higher pressure than single fractures, and CO₂ diffuses more efficiently than water due to its lower viscosity, although molecular size also influences transport. Coal's anisotropic permeability directs flow along high-permeability fractures, leading to uneven pressure distribution, preferential flow paths, and reduced sweep efficiency in lower-permeability zones. These results highlight the critical role of fracture connectivity and fluid properties in CO₂ migration and storage. By improving the understanding of fluid flow dynamics in fractured porous media, this paper provides valuable insights for enhancing CO₂ sequestration strategies, contributing to more effective carbon storage and greenhouse gas reduction efforts.</div></div>","PeriodicalId":100578,"journal":{"name":"Geoenergy Science and Engineering","volume":"251 ","pages":"Article 213904"},"PeriodicalIF":0.0,"publicationDate":"2025-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143838440","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fundamental physical properties of CO2 microbubbles in CO2-EOR effects of foam stabilizers, surfactants, and gas–liquid ratios","authors":"Donglei Liu ,&nbsp;Baocai Tong ,&nbsp;Kuo Li ,&nbsp;Sijia Wang ,&nbsp;Lanlan Jiang ,&nbsp;Yongchen Song","doi":"10.1016/j.geoen.2025.213890","DOIUrl":"10.1016/j.geoen.2025.213890","url":null,"abstract":"<div><div>Due to the favorable physical properties of microbubbles, injecting CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> microbubbles into formations is a novel and economical method to enhance the injectivity of traditional CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> injection methods. However, this approach demands higher stability of the bubbles. This study investigates the effects of commonly used foam stabilizer XG and foaming agent SDS, as well as the gas–liquid ratio, on the physical properties of microbubbles, including their quantity, diameter distribution, and stability, using microscopic image observation and potential measurement. Experiments were conducted using a microbubble generator to observe the physical properties of CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> microbubbles under different additive ratios. The results indicate that with an increase in the concentration of stabilizer XG, the diameter of the microbubbles initially increases and then decreases, showing varying trends across different diameter distributions. The study found that different rupture modes of the microbubbles are the reason for this trend. At the same mass fraction, SDS is a more effective foaming agent than Span20, increasing the number of microbubbles in the base liquid containing 0.1% wt XG to ten times the original amount, compared to 1.4 times with Span20. Additionally, the addition of XG polymer increased the potential of the CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> microbubble system from <span><math><mo>−</mo></math></span>11.6 mV to over <span><math><mo>−</mo></math></span>40 mV. However, after adding SDS to the XG solution, the potential decreased from <span><math><mo>−</mo></math></span>51 mV to below -40 mV, indicating that the synergistic interaction of XG polymer and SDS on the microbubble surface weakens their ability to enhance system stability. This study also explores the effects of the gas–water ratio and the reasons for the observed increase and then decrease in the number of microbubbles and the initial decrease followed by an increase in bubble size with the increase in gas–liquid volume ratio. The results of this study indicate that a stabilizer-to-foaming agent ratio of 0.1% XG + 0.01% SDS not only increases the number of microbubbles but also provides better stability.</div></div>","PeriodicalId":100578,"journal":{"name":"Geoenergy Science and Engineering","volume":"251 ","pages":"Article 213890"},"PeriodicalIF":0.0,"publicationDate":"2025-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143848213","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A novel thermal compositional simulator considering pseudo-local thermal non-equilibrium","authors":"Daniel Fuentes-Ibarra ,&nbsp;Octavio Cazarez-Candia ,&nbsp;Carlos G. Aguilar-Madera","doi":"10.1016/j.geoen.2025.213903","DOIUrl":"10.1016/j.geoen.2025.213903","url":null,"abstract":"<div><div>Reservoir simulation is essential for applying EOR techniques in oil fields. Improving mathematical models and studying their assumptions are crucial to accurately predicting mass and energy transport in reservoirs. Local thermal equilibrium (LTE) is a common assumption in most thermal process simulators. It assumes that the rock and fluids at any location and time share the same temperature, implying instantaneous energy transfer between hot fluids and the reservoir. However, recent developments suggest that this assumption may not always be reliable. Alternative energy models, such as pseudo-local thermal non-equilibrium (pseudo-LTNE) or thermal non-equilibrium (LTNE), may provide a more accurate representation of energy transport within porous media. In this paper, a compositional thermal simulator was developed involving pseudo-LTNE phenomena in thermal recovery processes. The simulator involves the molar balance equations for multiphase, multicomponent flow with phase change, and the energy equations for both LTE and pseudo-LTNE conditions. Results demonstrated that (1) the LTE assumption might not be valid under certain conditions, such as high fluid velocities and high injection temperatures, (2) pseudo-LTNE might have a greater impact on simulations for heavy oil compared to light or intermediate oils, (3) during thermal displacements, the pseudo-LTNE conditions were identified near the injection well over short periods and near the production well over long periods. These findings highlight the importance of incorporating both pseudo-LTNE and LTNE thermal conditions in reservoir simulations to improve the accuracy and efficiency of EOR processes, as well as ensuring robust and reliable performance of simulators in different scenarios.</div></div>","PeriodicalId":100578,"journal":{"name":"Geoenergy Science and Engineering","volume":"251 ","pages":"Article 213903"},"PeriodicalIF":0.0,"publicationDate":"2025-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143851923","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Triaxial permeability behaviors and structural damage evolution of deep hot dry rock under different cooling stimulation","authors":"Jun Lu ,&nbsp;Wang Jiang ,&nbsp;Junfeng Pan ,&nbsp;Jinyong Huang ,&nbsp;Jiayao Wu ,&nbsp;Delei Shang ,&nbsp;Mingyang Wu ,&nbsp;Gun Huang","doi":"10.1016/j.geoen.2025.213896","DOIUrl":"10.1016/j.geoen.2025.213896","url":null,"abstract":"<div><div>The geothermal exploitation of hot dry rock assumes a pivotal role in mitigating the global energy crisis and propelling the transformation of the energy structure towards a green and sustainable path. Thermal shock stimulation technology, as one of the fundamental and indispensable means in the development of hot dry rock geothermal resources, is capable of effectively augmenting reservoir permeability and enhancing the exploitation efficiency of geothermal resources by inducing micro-fracture networks. In this research, four distinct cooling methodologies, namely natural cooling, water cooling, liquid nitrogen cooling, and cycle liquid nitrogen cooling, were meticulously employed to conduct an in-depth exploration of the damage characteristics and permeability evolution behaviors of the granite pore structure under varying cooling conditions. The experimental findings clearly demonstrate that the pore structure of granite exhibits a pronounced dual-fractal characteristic under different cooling approaches. Moreover, an increase in the cooling rate is conducive to the formation of a more intricate pore and fracture distribution. Upon high-temperature cooling, the strength and ultrasonic wave velocity of granite are remarkably diminished. Low-temperature impact can significantly elevate the permeability of the reservoir, and notably, liquid nitrogen cycle cooling can enhance the permeability of the samples by several times compared to other methods. This study is poised to offer robust underpinnings for fracture creation and permeability enhancement in deep geothermal reservoirs.</div></div>","PeriodicalId":100578,"journal":{"name":"Geoenergy Science and Engineering","volume":"251 ","pages":"Article 213896"},"PeriodicalIF":0.0,"publicationDate":"2025-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143826116","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Oil displacement behavior of biosurfactant/chemically synthetic surfactant binary system in a microfluidic chip","authors":"Hong-Ze Gang ,&nbsp;Meng-Na Yang ,&nbsp;Qian-Qian Chen ,&nbsp;Zhi-Qing Su ,&nbsp;Gang-Zheng Sun ,&nbsp;Wei-Dong Wang ,&nbsp;Shi-Zhong Yang ,&nbsp;Ying-Cheng Li ,&nbsp;Bo-Zhong Mu","doi":"10.1016/j.geoen.2025.213902","DOIUrl":"10.1016/j.geoen.2025.213902","url":null,"abstract":"<div><div>Alkali-Surfactant (biosurfactant/petroleum-based surfactant formulation) -Polymer (ASP) flooding has been applied to enhance oil recovery in Daqing oilfield, however, the critical role of biosurfactant and petroleum-based surfactant have not been sufficiently explored. Here, the characteristics of biosurfactant, lipopeptides (LPs), and petroleum-based synthetic surfactant, heavy alkyl benzene sulfonate (HABS), and LPs/HABS binary formulation in displacing model oil were determined in a microfluidic chip. The images of the chip with a physical rock network and the injection pressure were simultaneously captured during the displacing process. The oil displacement characteristics of LPs/HABS binary formulation was quantitatively analyzed from the aspects of displacement efficiency, threshold pressure, swept area, displacement efficiency within swept area, and the distributions of remaining oil. Results revealed that LPs/HABS binary systems had the higher displacement efficiency and the lower values of threshold pressure. It was suggested that the lower interfacial tensions between LPs/HABS binary displacing solution and model oil induced higher value of capillary number, which effectively reduced the resistance for displacing solution when entering the pore structure of the network. As for the displacement efficiency in the swept region, LPs systems and LPs/HABS binary systems performed better to obtain higher displacement efficiency due to the superiority of LPs in wettability alteration. Results in the present work is beneficial for fundamental understand of microscopic displacement feature of lipopeptides/petroleum-based surfactant binary formations.</div></div>","PeriodicalId":100578,"journal":{"name":"Geoenergy Science and Engineering","volume":"251 ","pages":"Article 213902"},"PeriodicalIF":0.0,"publicationDate":"2025-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143838439","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study on the formation-wellbore coupling flow law during the drilling process of an oil-based drilling fluid system in deepwater fractured formations","authors":"Xin Yu ,&nbsp;Yonghai Gao ,&nbsp;Xuerui Wang ,&nbsp;Xinxin Zhao ,&nbsp;Bangtang Yin ,&nbsp;Baojiang Sun","doi":"10.1016/j.geoen.2025.213899","DOIUrl":"10.1016/j.geoen.2025.213899","url":null,"abstract":"<div><div>A reliable and accurate formation-wellbore coupling flow model is essential for deep-water managed pressure drilling, facilitating key decisions during the complex drilling process. This study develops a wellbore-formation coupled flow model tailored for oil-based drilling fluid systems in deep-water fractured formations, explicitly addressing the coexistence of overflow and lost circulation. The model comprehensively considers the combined effects of formation fluid invasion, mud loss, fluid coupling flow within the wellbore, fracture deformation, and fluid compression. This study uses the model to explore the evolution of overflow and lost circulation conditions and to analyze the impact of various overflow and lost circulation parameters and engineering operational parameters on gas invasion and loss rates. The results indicate that the gas invasion rate increases sharply under coupled flow conditions due to the dissolution and precipitation effects of the formation's intrusive gas. The decrease in frictional resistance along the annulus results in a loss rate significantly lower than that observed under lost circulation conditions when not accounting for wellbore-formation coupling flow. Due to drilling fluid losses, under coexisting gas invasion and lost circulation conditions, the sudden increase in the gas invasion rate occurs 0.16 h later than under conventional gas invasion conditions. In contrast, the gas invasion rate under overflow and lost circulation is slightly larger than that under the conventional gas invasion condition. Compared to the lost circulation condition, due to the dissolved gas precipitation effect, the loss rate under the coexistence of gas invasion and lost circulation experiences a significant drop, with the loss rate being only 63.2 % of that under conventional loss conditions.</div></div>","PeriodicalId":100578,"journal":{"name":"Geoenergy Science and Engineering","volume":"251 ","pages":"Article 213899"},"PeriodicalIF":0.0,"publicationDate":"2025-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143828880","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Acoustic emission insights into rock salt damage under humidity cycling","authors":"Zhen Zeng ,&nbsp;Hongling Ma ,&nbsp;Yinping Li ,&nbsp;Hang Li ,&nbsp;Xuan Wang ,&nbsp;Fahui Liu ,&nbsp;Kai Zhao","doi":"10.1016/j.geoen.2025.213898","DOIUrl":"10.1016/j.geoen.2025.213898","url":null,"abstract":"<div><div>Salt caverns used as compressed air energy storage (CAES) reservoirs undergo humidity cycling during operation, introducing moisture in the surrounding rock salt's cracks and influencing its mechanical properties. This study quantitatively examines the evolution of mesoscale (2–50 nm) structures and damage mechanisms associated with this effect. Acoustic emission (AE) was monitored during uniaxial compression tests on pre-damaged rock salt specimens subjected to humidity cycling. Real-time AE characteristics, such as count density, frequency, and amplitude, were utilized to identify sound sources within the rock, facilitating the analysis of the distribution and evolution of the associated structural damage throughout the macroscopic compression. The findings indicate that humidity cycling weakens the Felicity effect in damaged rock salt, with AE event counts decreasing by 59.2 % while the outbreak of AE was significantly delayed. AE signal frequency and amplitude progressively decreased, indicating a transition from high-energy transgranular cracking to lower-intensity damage such as intergranular cracking and void closure. RA-AF analysis revealed an increase in tensile crack proportion from 44.39 % to 59.11 %. Combined with mesoscale observation, self-healing effects in damaged rock salt were confirmed, and the relationship between the mesoscale damage mechanisms and macroscopic mechanical responses of rock salt under humidity cycling was elucidated. Recrystallized salt structures bridged the cracks, mitigating stress concentration at crack tips and suppressing secondary crack propagation. These structures facilitated releasing strain energy in small increments during the later loading stage, delaying high-energy fracture events. Additionally, brine inclusion within cracks reduced intergranular damage and enhanced rock deformation. Consequently, humidity cycling improves the compressive strength and ductility of damaged rock salt. These insights facilitate predictions of the mechanical properties of rocks surrounding CAES salt caverns, enabling a more accurate assessment of reservoirs' geological safety under long-term operation.</div></div>","PeriodicalId":100578,"journal":{"name":"Geoenergy Science and Engineering","volume":"251 ","pages":"Article 213898"},"PeriodicalIF":0.0,"publicationDate":"2025-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143821303","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental investigation of the impact of short-term hydrogen exposure on cement sheath's mechanical and sealing integrity","authors":"Diana Maury Fernandez,&nbsp;Hossein Emadi,&nbsp;Athar Hussain,&nbsp;Sugan Raj Thiyagarajan,&nbsp;Ion Ispas,&nbsp;Marshall Watson","doi":"10.1016/j.geoen.2025.213885","DOIUrl":"10.1016/j.geoen.2025.213885","url":null,"abstract":"<div><div>The effect of hydrogen exposure on cement is a topic of great interest due to its significance in the safety and security of Underground Hydrogen Storage (UHS) in geological structures. Any alteration to cement properties can affect the wellbore isolation capacity or induce premature failure, compromising the reliability and safety of UHS projects. While over the past decade, various studies have been conducted on this topic, the effect of hydrogen on cement's mechanical and sealing integrity remains unclear. This study aims to evaluate the impact of different short-term hydrogen exposure timeframes on the performance of Class H neat cement under geological storage conditions. Multiple cement samples were prepared, cured, and exposed to pure H₂ for 7, 14, 21, and 28 days in a core holder at controlled pressure and temperature conditions (49 °C, 10.34 MPa). The effect of hydrogen on cement's sealing abilities was evaluated by monitoring alterations in petrophysical properties like porosity and permeability. Cement's mechanical integrity was evaluated by measuring properties such as Young's Modulus, Poisson's ratio, Unconfined Compressive Strength, and Tensile Strength before and after exposure. Other techniques like Computer Tomography (CT) scanning and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) were used to further understand cement's interaction with hydrogen. The most significantly affected properties were permeability, ultimate strengths, and elastic properties. The creation of microfractures following the hydrogen pressurization for 14, 21, and 28 days was observed, which suggests cement presents a less rigid behavior under these conditions. Variations in cement compositional elements were found, with predominant reductions in Calcium (Ca) and Oxygen (O), as well as Carbon (C) enrichment. The results of this study provide a further understanding of hydrogen effects on cement's mechanical and sealing integrity and valuable insight into the wellbore integrity implications in UHS projects.</div></div>","PeriodicalId":100578,"journal":{"name":"Geoenergy Science and Engineering","volume":"251 ","pages":"Article 213885"},"PeriodicalIF":0.0,"publicationDate":"2025-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143829185","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characterizations of phase behavior and miscibility of CO2-hydrocarbon mixtures in bulk and porous media using low-field NMR technique","authors":"Heng Wang ,&nbsp;Yuchen Xin ,&nbsp;Yanbin Gong ,&nbsp;Chunyu He ,&nbsp;Pufu Xiao ,&nbsp;Yangwen Zhu ,&nbsp;Haiying Liao ,&nbsp;Haiyan Zhu ,&nbsp;Zhiwu Li ,&nbsp;Bryan X. Medina-Rodriguez","doi":"10.1016/j.geoen.2025.213900","DOIUrl":"10.1016/j.geoen.2025.213900","url":null,"abstract":"<div><div>Low-filed Nuclear Magnetic Resonance (LF-NMR) technique has been widely used to characterize rock properties and to investigate performance of CO₂ EOR. However, rare studies have been found to characterize the complex phase behavior variations in CO₂-oil systems using the LF-NMR technique, i.e. interfacial tension reduction, viscosity reduction, oil swelling, hydrocarbon extraction and miscibility between gas-oil phases when pressure exceeds the minimum miscible pressure (MMP). This study explores the phase behavior and miscibility of CO₂-hydrocarbon mixtures using the low-field nuclear magnetic resonance (NMR) techniques. First, the transverse relaxation time (T₂) of n-dodecane (C12) and n-hexadecane (C16) at different pressure and temperature conditions were measured as a baseline. Results show that the logarithm mean of T₂ (T_2lm) has a good linear relationship with viscosity. Thereafter, T₂ distributions of CO₂-hydrocarbon mixtures were continuously collected to investigate the evolutions of phase behavior induced by CO₂-hydrocarbon interactions. Three stages were categorized from the T_2lm of CO₂-hydrocarbon mixtures and pressure. As pressure increases for all cases, there is an observable rise in T_2lm values due to the viscosity reduction after CO₂ dissolution. At the subsequent higher pressures, as more CO₂ dissolves into the oil phase, the molecular mobility of oil components decreases due to increased intermolecular interactions and reduced free mean path. This effect causes a decline in T_2lm values, as the motion of oil molecules becomes more restricted. Finally, T_2lm stabilizes when miscibility is achieved, as the CO₂-oil system transitions into a single-phase state Similar findings were observed for CO₂-C12/C16 mixtures in glass-bead packs. In addition, interactions between CO₂ and light oil mixtures were investigated to validate the new technique. Results show that the MMP of the mixture is 8.5 MPa. As for CO₂-oil in core plug, T_2lm increases first and stabilizes below and above the MMP, while higher pressure accelerates the stabilization process. This might be because oil close to the gaseous CO₂ becomes miscible, while for oil in the smaller pore spaces, a fully CO₂-saturated phase exits as multi-contact miscible cannot be achieved simply through molecular diffusion. The findings in this study reveal the dynamic interactions between CO₂ and oil and provide an effective method for estimating the MMP, illustrating a significant potential application for commercial-scale CO₂ EOR and storage projects.</div></div>","PeriodicalId":100578,"journal":{"name":"Geoenergy Science and Engineering","volume":"251 ","pages":"Article 213900"},"PeriodicalIF":0.0,"publicationDate":"2025-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143848212","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}