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20 pages, 11478 KiB  
Article
Pore Evolution and Fractal Characteristics of Marine Shale: A Case Study of the Silurian Longmaxi Formation Shale in the Sichuan Basin
by Hongzhan Zhuang, Yuqiang Jiang, Quanzhong Guan, Xingping Yin and Yifan Gu
Fractal Fract. 2025, 9(8), 492; https://doi.org/10.3390/fractalfract9080492 - 28 Jul 2025
Viewed by 288
Abstract
The Silurian marine shale in the Sichuan Basin is currently the main reservoir for shale gas reserves and production in China. This study investigates the reservoir evolution of the Silurian marine shale based on fractal dimension, quantifying the complexity and heterogeneity of the [...] Read more.
The Silurian marine shale in the Sichuan Basin is currently the main reservoir for shale gas reserves and production in China. This study investigates the reservoir evolution of the Silurian marine shale based on fractal dimension, quantifying the complexity and heterogeneity of the shale’s pore structure. Physical simulation experiments were conducted on field-collected shale samples, revealing the evolution of total organic carbon, mineral composition, porosity, and micro-fractures. The fractal dimension of shale pore was characterized using the Frenkel–Halsey–Hill and capillary bundle models. The relationships among shale components, porosity, and fractal dimensions were investigated through a correlation analysis and a principal component analysis. A comprehensive evolution model for porosity and micro-fractures was established. The evolution of mineral composition indicates a gradual increase in quartz content, accompanied by a decline in clay, feldspar, and carbonate minerals. The thermal evolution of organic matter is characterized by the formation of organic pores and shrinkage fractures on the surface of kerogen. Retained hydrocarbons undergo cracking in the late stages of thermal evolution, resulting in the formation of numerous nanometer-scale organic pores. The evolution of inorganic minerals is represented by compaction, dissolution, and the transformation of clay minerals. Throughout the simulation, porosity evolution exhibited distinct stages of rapid decline, notable increase, and relative stabilization. Both pore volume and specific surface area exhibit a trend of decreasing initially and then increasing during thermal evolution. However, pore volume slowly decreases after reaching its peak in the late overmature stage. Fractal dimensions derived from the Frenkel–Halsey–Hill model indicate that the surface roughness of pores (D1) in organic-rich shale is generally lower than the complexity of their internal structures (D2) across different maturity levels. Additionally, the average fractal dimension calculated based on the capillary bundle model is higher, suggesting that larger pores exhibit more complex structures. The correlation matrix indicates a co-evolution relationship between shale components and pore structure. Principal component analysis results show a close relationship between the porosity of inorganic pores, microfractures, and fractal dimension D2. The porosity of organic pores, the pore volume and specific surface area of the main pore size are closely related to fractal dimension D1. D1 serves as an indicator of pore development extent and characterizes the changes in components that are “consumed” or “generated” during the evolution process. Based on mineral composition, fractal dimensions, and pore structure evolution, a comprehensive model describing the evolution of pores and fractal dimensions in organic-rich shale was established. Full article
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16 pages, 1188 KiB  
Article
Preparation and Performance Evaluation of Modified Amino-Silicone Supercritical CO2 Viscosity Enhancer for Shale Oil and Gas Reservoir Development
by Rongguo Yang, Lei Tang, Xuecheng Zheng, Yuanqian Zhu, Chuanjiang Zheng, Guoyu Liu and Nanjun Lai
Processes 2025, 13(8), 2337; https://doi.org/10.3390/pr13082337 - 23 Jul 2025
Viewed by 339
Abstract
Against the backdrop of global energy transition and strict environmental regulations, supercritical carbon dioxide (scCO2) fracturing and oil displacement technologies have emerged as pivotal green approaches in shale gas exploitation, offering the dual advantages of zero water consumption and carbon sequestration. [...] Read more.
Against the backdrop of global energy transition and strict environmental regulations, supercritical carbon dioxide (scCO2) fracturing and oil displacement technologies have emerged as pivotal green approaches in shale gas exploitation, offering the dual advantages of zero water consumption and carbon sequestration. However, the inherent low viscosity of scCO2 severely restricts its sand-carrying capacity, fracture propagation efficiency, and oil recovery rate, necessitating the urgent development of high-performance thickeners. The current research on scCO2 thickeners faces a critical trade-off: traditional fluorinated polymers exhibit excellent philicity CO2, but suffer from high costs and environmental hazards, while non-fluorinated systems often struggle to balance solubility and thickening performance. The development of new thickeners primarily involves two directions. On one hand, efforts focus on modifying non-fluorinated polymers, driven by environmental protection needs—traditional fluorinated thickeners may cause environmental pollution, and improving non-fluorinated polymers can maintain good thickening performance while reducing environmental impacts. On the other hand, there is a commitment to developing non-noble metal-catalyzed siloxane modification and synthesis processes, aiming to enhance the technical and economic feasibility of scCO2 thickeners. Compared with noble metal catalysts like platinum, non-noble metal catalysts can reduce production costs, making the synthesis process more economically viable for large-scale industrial applications. These studies are crucial for promoting the practical application of scCO2 technology in unconventional oil and gas development, including improving fracturing efficiency and oil displacement efficiency, and providing new technical support for the sustainable development of the energy industry. This study innovatively designed an amphiphilic modified amino silicone oil polymer (MA-co-MPEGA-AS) by combining maleic anhydride (MA), methoxy polyethylene glycol acrylate (MPEGA), and amino silicone oil (AS) through a molecular bridge strategy. The synthesis process involved three key steps: radical polymerization of MA and MPEGA, amidation with AS, and in situ network formation. Fourier transform infrared spectroscopy (FT-IR) confirmed the successful introduction of ether-based CO2-philic groups. Rheological tests conducted under scCO2 conditions demonstrated a 114-fold increase in viscosity for MA-co-MPEGA-AS. Mechanistic studies revealed that the ether oxygen atoms (Lewis base) in MPEGA formed dipole–quadrupole interactions with CO2 (Lewis acid), enhancing solubility by 47%. Simultaneously, the self-assembly of siloxane chains into a three-dimensional network suppressed interlayer sliding in scCO2 and maintained over 90% viscosity retention at 80 °C. This fluorine-free design eliminates the need for platinum-based catalysts and reduces production costs compared to fluorinated polymers. The hierarchical interactions (coordination bonds and hydrogen bonds) within the system provide a novel synthetic paradigm for scCO2 thickeners. This research lays the foundation for green CO2-based energy extraction technologies. Full article
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16 pages, 3833 KiB  
Article
Seven Thousand Felt Earthquakes in Oklahoma and Kansas Can Be Confidently Traced Back to Oil and Gas Activities
by Iason Grigoratos, Alexandros Savvaidis and Stefan Wiemer
GeoHazards 2025, 6(3), 36; https://doi.org/10.3390/geohazards6030036 - 15 Jul 2025
Viewed by 265
Abstract
The seismicity levels in Oklahoma and southern Kansas have increased dramatically over the last 15 years. Past studies have identified the massive disposal of wastewater co-produced during oil and gas extraction as the driving force behind some earthquake clusters, with a small number [...] Read more.
The seismicity levels in Oklahoma and southern Kansas have increased dramatically over the last 15 years. Past studies have identified the massive disposal of wastewater co-produced during oil and gas extraction as the driving force behind some earthquake clusters, with a small number of events directly linked to hydraulic fracturing (HF) stimulations. The present investigation is the first one to examine the role both of these activities played throughout the two states, under the same framework. Our findings confirm that wastewater disposal is the main causal factor, while also identifying several previously undocumented clusters of seismicity that were triggered by HF. We were able to identify areas where both causal factors spatially coincide, even though they act at distinct depth intervals. Overall, oil and gas operations are probabilistically linked at high confidence levels with more than 7000 felt earthquakes (M ≥ 2.5), including 46 events with M ≥ 4.0 and 4 events with M ≥ 5. Our analysis utilized newly compiled regional earthquake catalogs and established physics-based principles. It first hindcasts the seismicity rates after 2012 on a spatial grid using either real or randomized HF and wastewater data as the input, and then compares them against the null hypothesis of purely tectonic loading. In the end, each block is assigned a p-value, reflecting the statistical confidence in its causal association with either HF stimulations or wastewater disposal. Full article
(This article belongs to the Special Issue Seismological Research and Seismic Hazard & Risk Assessments)
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24 pages, 6478 KiB  
Article
Numerical Simulation of Multi-Cluster Fracture Propagation in Marine Natural Gas Hydrate Reservoirs
by Lisha Liao, Youkeren An, Jinshan Wang, Yiqun Zhang, Lerui Liu, Meihua Chen, Yiming Gao and Jiayi Han
J. Mar. Sci. Eng. 2025, 13(7), 1224; https://doi.org/10.3390/jmse13071224 - 25 Jun 2025
Viewed by 219
Abstract
Natural gas hydrates (NGHs) are promising energy resources, although their marine exploitation is limited by low reservoir permeability and hydrate decomposition efficiency. Multi-cluster fracturing technology can enhance reservoir permeability, yet complex properties of hydrate sediments render the prediction of fracture behavior challenging. Therefore, [...] Read more.
Natural gas hydrates (NGHs) are promising energy resources, although their marine exploitation is limited by low reservoir permeability and hydrate decomposition efficiency. Multi-cluster fracturing technology can enhance reservoir permeability, yet complex properties of hydrate sediments render the prediction of fracture behavior challenging. Therefore, we developed a three-dimensional (3D) fluid–solid coupling model for hydraulic fracturing in NGH reservoirs based on cohesive elements to analyze the effects of sediment plasticity, hydrate saturation, fracturing fluid viscosity, and injection rate, as well as the stress interference mechanisms in multi-cluster simultaneous fracturing under different cluster spacings. Results show that selecting low-plastic reservoirs with high hydrate saturation (SH > 50%) and adopting an optimal combination of fracturing fluid viscosity and injection rate can achieve the co-optimization of stimulated reservoir volume (SRV) and cross-layer risk. In multi-cluster fracturing, inter-fracture stress interference promotes the propagation of fractures along the fracture plane while suppressing it in the normal direction of the fracture plane, and this effect diminishes significantly till 9 m cluster spacing. This study provides valuable insights for the selection of optimal multi-cluster fracturing parameters for marine NGH reservoirs. Full article
(This article belongs to the Section Geological Oceanography)
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21 pages, 2249 KiB  
Article
Multifractal Characterization of Full-Scale Pore Structure in Middle-High-Rank Coal Reservoirs: Implications for Permeability Modeling in Western Guizhou–Eastern Yunnan Basin
by Fangkai Quan, Yanhui Zhang, Wei Lu, Chongtao Wei, Xuguang Dai and Zhengyuan Qin
Processes 2025, 13(6), 1927; https://doi.org/10.3390/pr13061927 - 18 Jun 2025
Viewed by 443
Abstract
This study presents a comprehensive multifractal characterization of full-scale pore structures in middle- to high-rank coal reservoirs from the Western Guizhou–Eastern Yunnan Basin and establishes a permeability prediction model integrating fractal heterogeneity and pore throat parameters. Eight coal samples were analyzed using mercury [...] Read more.
This study presents a comprehensive multifractal characterization of full-scale pore structures in middle- to high-rank coal reservoirs from the Western Guizhou–Eastern Yunnan Basin and establishes a permeability prediction model integrating fractal heterogeneity and pore throat parameters. Eight coal samples were analyzed using mercury intrusion porosimetry (MIP), low-pressure gas adsorption (N2/CO2), and multifractal theory to quantify multiscale pore heterogeneity and its implications for fluid transport. Results reveal weak correlations (R2 < 0.39) between conventional petrophysical parameters (ash yield, volatile matter, porosity) and permeability, underscoring the inadequacy of bulk properties in predicting flow behavior. Full-scale pore characterization identified distinct pore architecture regimes: Laochang block coals exhibit microporous dominance (0.45–0.55 nm) with CO2 adsorption capacities 78% higher than Tucheng samples, while Tucheng coals display enhanced seepage pore development (100–5000 nm), yielding 2.5× greater stage pore volumes. Multifractal analysis demonstrated significant heterogeneity (Δα = 0.98–1.82), with Laochang samples showing superior pore uniformity (D1 = 0.86 vs. 0.82) but inferior connectivity (D2 = 0.69 vs. 0.71). A novel permeability model was developed through multivariate regression, integrating the heterogeneity index (Δα) and effective pore throat diameter (D10), achieving exceptional predictive accuracy. The strong negative correlation between Δα and permeability (R = −0.93) highlights how pore complexity governs flow resistance, while D10’s positive influence (R = 0.72) emphasizes throat size control on fluid migration. This work provides a paradigm shift in coal reservoir evaluation, demonstrating that multiscale fractal heterogeneity, rather than conventional bulk properties, dictates permeability in anisotropic coal systems. The model offers critical insights for optimizing hydraulic fracturing and enhanced coalbed methane recovery in structurally heterogeneous basins. Full article
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23 pages, 3535 KiB  
Article
Geological–Engineering Synergistic Optimization of CO2 Flooding Well Patterns for Sweet Spot Development in Tight Oil Reservoirs
by Enhui Pei, Chao Xu and Chunsheng Wang
Sustainability 2025, 17(11), 4751; https://doi.org/10.3390/su17114751 - 22 May 2025
Cited by 1 | Viewed by 430
Abstract
CO2 flooding technology has been established as a key technique that is both economically viable and environmentally sustainable, achieving enhanced oil recovery (EOR) while advancing CCUS objectives. This study addresses the challenge of optimizing CO2 flooding well patterns in tight oil [...] Read more.
CO2 flooding technology has been established as a key technique that is both economically viable and environmentally sustainable, achieving enhanced oil recovery (EOR) while advancing CCUS objectives. This study addresses the challenge of optimizing CO2 flooding well patterns in tight oil reservoirs through a geological–engineering integrated approach. A semi-analytical model incorporating startup pressure gradients and miscible/immiscible two-phase flow was developed to dynamically adjust injection intensity. An effective driving coefficient model considering reservoir heterogeneity and fracture orientation was proposed to determine well pattern boundaries. Field data from Blocks A and B were used to validate the models, with the results indicating optimal injection intensities of 0.39 t/d/m and 0.63 t/d/m, respectively. Numerical simulations confirmed that inverted five-spot patterns with well spacings of 240 m (Block A) and 260 m (Block B) achieved the highest incremental oil production (3621.6 t/well and 4213.1 t/well) while reducing the gas channeling risk by 35–47%. The proposed methodology provides a robust framework for enhancing recovery efficiency in low-permeability reservoirs under varying geological conditions. Full article
(This article belongs to the Special Issue Sustainable Exploitation and Utilization of Hydrocarbon Resources)
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5 pages, 155 KiB  
Editorial
New Advances in Low-Energy Processes for Geo-Energy Development
by Daoyi Zhu
Energies 2025, 18(9), 2357; https://doi.org/10.3390/en18092357 - 6 May 2025
Viewed by 430
Abstract
The development of geo-energy resources, including oil, gas, and geothermal reservoirs, is being transformed through the creation of low-energy processes and innovative technologies. This Special Issue compiles cutting-edge research aimed at enhancing efficiency, sustainability, and recovery during geo-energy extraction. The published studies explore [...] Read more.
The development of geo-energy resources, including oil, gas, and geothermal reservoirs, is being transformed through the creation of low-energy processes and innovative technologies. This Special Issue compiles cutting-edge research aimed at enhancing efficiency, sustainability, and recovery during geo-energy extraction. The published studies explore a diverse range of methodologies, such as the nanofluidic analysis of shale oil phase transitions, deep electrical resistivity tomography for geothermal exploration, and hybrid AI-driven production prediction models. Their key themes include hydraulic fracturing optimization, CO2 injection dynamics, geothermal reservoir simulation, and competitive gas–water adsorption in ultra-deep reservoirs, and these studies combine advanced numerical modeling, experimental techniques, and field applications to address challenges in unconventional reservoirs, geothermal energy exploitation, and enhanced oil recovery. By bridging theoretical insights with practical engineering solutions, this Special Issue provides a comprehensive foundation for future innovations in low-energy geo-energy development. Full article
(This article belongs to the Special Issue New Advances in Low-Energy Processes for Geo-Energy Development)
22 pages, 12751 KiB  
Article
Seismic Signals of the Wushi MS7.1 Earthquake of 23 January 2024, Viewed Through the Angle of Hydrogeochemical Characteristics
by Zhaojun Zeng, Xiaocheng Zhou, Jinyuan Dong, Jingchao Li, Miao He, Jiao Tian, Yuwen Wang, Yucong Yan, Bingyu Yao, Shihan Cui, Gaoyuan Xing, Han Yan, Ruibing Li, Wan Zheng and Yueju Cui
Appl. Sci. 2025, 15(9), 4791; https://doi.org/10.3390/app15094791 - 25 Apr 2025
Viewed by 551
Abstract
On 23 January 2024, a MS7.1 earthquake struck Wushi County, Xinjiang Uygur Autonomous Region, marking the largest seismic event in the Southern Tianshan (STS) region in the past century. This study investigates the relationship between hydrothermal fluid circulation and seismic activity [...] Read more.
On 23 January 2024, a MS7.1 earthquake struck Wushi County, Xinjiang Uygur Autonomous Region, marking the largest seismic event in the Southern Tianshan (STS) region in the past century. This study investigates the relationship between hydrothermal fluid circulation and seismic activity by analyzing the chemical composition and origin of fluids in natural hot springs along the Maidan Fracture (MDF). Results reveal two distinct hydrochemical water types (Ca-HCO3 and Ca-Mg-Cl). The δD and δ18O values indicating spring water are influenced by atmospheric precipitation input and altitude. Circulation depths (621–3492 m) and thermal reservoir temperatures (18–90 °C) were estimated. Notably, the high 3He/4He ratios (3.71 Ra) and mantle-derived 3He content reached 46.48%, confirming that complex gas–water–rock interactions occur at fracture intersections. Continuous monitoring at site S13 (144 km from the epicenter of the Wushi MS7.1 earthquake) captured pre-and post-seismic hydrogeochemical fingerprints linked to the Wushi MS7.1 earthquake. Stress accumulation along the MDF induced permeability changes, perturbing hydrogeochemical equilibrium. At 42 days pre-Wushi MS7.1 earthquake, δ13C DIC exceeded +2σ thresholds (−2.12‰), signaling deep fracture expansion and CO2 release. By 38 days pre-Wushi MS7.1 earthquake, Na+, SO42−, and δ18O surpassed 2σ levels, reflecting hydraulic connection between deep-seated and shallow fracture networks. Ion concentrations and isotope values showed dynamic shifts during the earthquake, which revealed episodic stress transfer along fault asperities. Post-Wushi MS7.1 earthquake, fracture closure reduced deep fluid input, causing δ13C DIC to drop to −4.89‰, with ion concentrations returning to baseline within 34 days. Trace elements such as Be and Sr exhibited anomalies 12 days before the Wushi MS7.1 earthquake, while elements like Li, B, and Rb showed anomalies 24 days after the Wushi MS7.1 earthquake. Hydrochemical monitoring of hot springs captures such critical stress-induced signals, offering vital insights for earthquake forecasting in tectonically active regions. Full article
(This article belongs to the Section Earth Sciences)
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17 pages, 7177 KiB  
Article
Wear Resistance of the Refractory WC–Co Diamond-Reinforced Composite with Zirconia Additive
by Boranbay Ratov, Volodymyr Mechnik, Edvin Hevorkian, Miroslaw Rucki, Daniel Pieniak, Nikolai Bondarenko, Vasyl Kolodnitskyi, Sergii Starik, Viktor Bilorusets, Volodymyr Chishkala, Perizat Sundetova, Aldabergen Bektilevov, Anar Shukmanova and Askar Seidaliyev
Materials 2025, 18(9), 1965; https://doi.org/10.3390/ma18091965 - 25 Apr 2025
Viewed by 758
Abstract
This paper provides deeper insights into the performance of diamond particulate reinforced refractory composites used for cutting tools in the oil and gas industries. In particular, 25Cdiamond–70.5WC–4.5Co composites were enhanced with zirconia additives in proportions of 4 wt.% and 10 wt.% [...] Read more.
This paper provides deeper insights into the performance of diamond particulate reinforced refractory composites used for cutting tools in the oil and gas industries. In particular, 25Cdiamond–70.5WC–4.5Co composites were enhanced with zirconia additives in proportions of 4 wt.% and 10 wt.% via the spark plasma sintering method. Wear tests were performed, and the analyses of elemental composition, morphology, and microstructure were completed. It was found that the addition of yttria-stabilized zirconia increased the plasticity of the matrix and thus introduced the ductile fracture mechanism, reducing the role of abrasive wear. As a result, the specific wear rate was reduced by 44% after the addition of 4 wt.% of zirconia and by 80% with 10 wt.% of ZrO2. The presence of zirconia contributed to the increase in the retention force between the matrix and diamond grits, which further reduced the intensity of the abrasive mechanism. Full article
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20 pages, 7716 KiB  
Article
Fractal Characterization of a Multi-Scale Pore Structure in Ultra-Deep Coal Seams
by Yanwei Qu, Feng Chen, Lulu Ma, Peiwen Jiang, Bing Li, Jiangang Ren, Runsheng Lv, Gaofeng Liu, Zhimin Song, Ping Chang and George Barakos
Fractal Fract. 2025, 9(4), 250; https://doi.org/10.3390/fractalfract9040250 - 15 Apr 2025
Cited by 1 | Viewed by 547
Abstract
The pore–fracture structure of ultra-deep coal is critical for evaluating resource potential and guiding the exploration and development of deep coalbed methane (CBM). In this study, a coal sample was obtained from the Gaogu-4 well at a depth of 4369.4 m in the [...] Read more.
The pore–fracture structure of ultra-deep coal is critical for evaluating resource potential and guiding the exploration and development of deep coalbed methane (CBM). In this study, a coal sample was obtained from the Gaogu-4 well at a depth of 4369.4 m in the Shengli Oilfield of Shandong, China. A comprehensive suite of characterization techniques, including Field Emission Scanning Electron Microscopy (FE-SEM), X-ray diffraction (XRD), Mercury Intrusion Porosimetry (MIP), Low-temperature Nitrogen Adsorption (LT-N2GA), and Low-pressure CO2 Adsorption (LP-CO2GA), were employed to investigate the surface morphology, mineral composition, and multi-scale pore–fracture characteristics of the ultra-deep coal. Based on fractal geometry theory, four fractal dimension models were established, and the pore structure parameters were then used to calculate the fractal dimensions of the coal sample. The results show that the ultra-deep coal surface is relatively rough, with prominent fractures and limited pore presence as observed under FE-SEM. Energy Dispersive Spectrometer (EDS) analysis identified the elements such as C, O, Al, Si, S, and Fe, thus suggesting that the coal sample contains silicate and iron sulfide minerals. XRD analysis shows that the coal sample contains kaolinite, marcasite, and clinochlore. The multi-scale pore–fracture structure characteristics indicate that the ultra-deep coal is predominantly composed of micropores, followed by mesopores. Macropores are the least abundant, yet they contribute the most to pore volume (PV), accounting for 70.9%. The specific surface area (SSA) of micropores occupies an absolute advantage, accounting for up to 97.46%. Based on the fractal model, the fractal dimension of the coal surface is 1.4372, while the fractal dimensions of the micropores, mesopores, and macropores are 2.5424, 2.5917, and 2.5038, respectively. These results indicate that the surface morphology and pore–fracture distribution of the ultra-deep coal are non-uniform and exhibit statistical fractal characteristics. The pore–fracture structure dominated by micropores in ultra-deep coal seams provides numerous adsorption sites for CBM, thereby controlling the adsorption capacity and development potential of deep CBM. Full article
(This article belongs to the Special Issue Fractal Analysis and Its Applications in Rock Engineering)
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18 pages, 1269 KiB  
Review
Exploration and Application of Natural Gas Injection, Water Injection and Fracturing Technologies in Low-Permeability Reservoirs in China
by Xiaoliang Zhao and Xingyan Qi
Processes 2025, 13(3), 855; https://doi.org/10.3390/pr13030855 - 14 Mar 2025
Cited by 1 | Viewed by 802
Abstract
This article provides an overview of low-permeability reservoir development technologies, including carbon dioxide injection, nitrogen injection, air injection, natural gas injection, water injection (unstable water injection, advanced water injection), water–gas alternating injection, and hydraulic fracturing (hydraulic fracturing, repeated fracturing). These technologies have their [...] Read more.
This article provides an overview of low-permeability reservoir development technologies, including carbon dioxide injection, nitrogen injection, air injection, natural gas injection, water injection (unstable water injection, advanced water injection), water–gas alternating injection, and hydraulic fracturing (hydraulic fracturing, repeated fracturing). These technologies have their own strengths and weaknesses in improving crude oil recovery and are significantly constrained by reservoir characteristics. This article uses specific cases such as the increase in CO2 injection pressure in Yaoyingtai oilfield, which significantly improves recovery rate, nitrogen injection in Zhongyuan oilfield, which increases adjacent well production and single-well recovery rate, air injection in a certain block of Changqing oilfield, natural gas injection in Yushulin oilfield, which has the best effect under specific pressure, as well as the effects and problems of water injection technology, the increasing production effect, and potential risks of hydraulic fracturing, to deeply analyze the application effectiveness and influencing factors of various technologies. Through comparative analysis, it can be concluded that CO2 injection has corrosion and gas channeling problems, nitrogen injection is limited by solubility, oxygen consumption in air injection is affected by temperature and pressure, natural gas injection is constrained by reservoir structure, water injection technology is unstable and difficult to determine timings, and fracturing technology faces difficulties in energy replenishment and time determination. Therefore, optimizing and applying these technologies rationally is of great significance for the efficient development of low-permeability reservoirs. Full article
(This article belongs to the Special Issue Recent Developments in Enhanced Oil Recovery (EOR) Processes)
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16 pages, 5102 KiB  
Article
Tröger’s Base Polyimide Membranes with Enhanced Mechanical Robustness for Gas Separation
by Xingfeng Lei, Zixiang Zhang, Yuyang Xiao, Qinyu Yu, Yewei Liu, Xiaohua Ma and Qiuyu Zhang
Polymers 2025, 17(4), 524; https://doi.org/10.3390/polym17040524 - 18 Feb 2025
Viewed by 1002
Abstract
The rigid V-shaped Tröger’s base (TB) unit has been proven efficacious in creating microporosity, making TB-based polyimides (PIs) exhibiting significant advantages in simultaneously increasing gas permeability and selectivity for the separation industry. However, TB-based PIs commonly display undesired mechanical [...] Read more.
The rigid V-shaped Tröger’s base (TB) unit has been proven efficacious in creating microporosity, making TB-based polyimides (PIs) exhibiting significant advantages in simultaneously increasing gas permeability and selectivity for the separation industry. However, TB-based PIs commonly display undesired mechanical performance due to the low molecular weight resulting from the evident steric hindrance and low reactivity of TB-containing diamines. Herein, a novel diamine-containing bisimide linkage (BIDA) has been synthesized and then polymerized with paraformaldehyde via a moderate “TB polymerization” strategy to furnish polymers simultaneously, including imide linkages and TB units in the polymer main chains, namely, TB-PIs. This TB polymerization strategy avoids the direct polymerization of dianhydride with low-reactivity TB diamine. After incorporating a meta-methyl substituent into BIDA diamine, the m-MBIDA diamine-derived m-MTBPI ultimately exhibits a high molecular weight, good tensile strength (90.4 MPa) and an outstanding fracture toughness (45.1 MJ/m3). And more importantly, the m-MTBPI membrane displays an evidently enhanced gas separation ability in comparison with BIDA-derived TBPI, with overall separation properties much closer to the 1991 Robeson upper bound. Moreover, no sign of plasticization appears for the m-MTBPI membrane when separating a high-pressure CO2/CH4 mixture (v/v = 1/1) up to 20 bar, with the CO2/CH4 mixed-gas separation performance approaching the 2018 upper bound. Full article
(This article belongs to the Special Issue Advances in High-Performance Polymer Materials)
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16 pages, 4163 KiB  
Article
Two-Phase Production Performance of Multistage Fractured Horizontal Wells in Shale Gas Reservoir
by Hongsha Xiao, Siliang He, Man Chen, Changdi Liu, Qianwen Zhang and Ruihan Zhang
Processes 2025, 13(2), 563; https://doi.org/10.3390/pr13020563 - 17 Feb 2025
Cited by 1 | Viewed by 623
Abstract
Shale gas extraction is hindered by the complex geological conditions of shale reservoirs, such as deep burial, low permeability, and multi-zone characteristics. Therefore, horizontal well hydraulic fracturing is essential for improving reservoir permeability. However, fracture interference and fracturing fluid retention can lead to [...] Read more.
Shale gas extraction is hindered by the complex geological conditions of shale reservoirs, such as deep burial, low permeability, and multi-zone characteristics. Therefore, horizontal well hydraulic fracturing is essential for improving reservoir permeability. However, fracture interference and fracturing fluid retention can lead to gas–water co-production. Existing models for predicting the productivity of fractured horizontal wells typically focus on single-phase flow or do not fully account for fracture interactions and dynamic water saturation changes. In contrast, this study introduces a novel fast prediction model for the steady-state productivity of fractured horizontal wells under a gas–water two-phase flow. The model extends single-phase fluid seepage theory by incorporating a gas–water two-phase pseudo-pressure function, while also accounting for fracture interference using potential theory and the superposition principle. Furthermore, it dynamically integrates formation pressure and water saturation variations, offering a more accurate prediction of productivity. The result demonstrates that fracture interference significantly affects the distribution of productivity, with end fractures producing up to 5.6 × 104 m3 while intermediate fractures maintain a relatively uniform production of around 0.9 × 104 m3. The sensitivity analysis reveals that productivity increases with an increase in formation pressure, fracture number, fracture half-length, and fracture angle, while an increcase in water saturation and skin factor reduce it. These results highlight the importance of optimizing fracture design and production strategies. This work provides a more comprehensive and efficient method for predicting and optimizing the gas–water two-phase productivity of fractured horizontal wells. Full article
(This article belongs to the Special Issue Advances in Enhancing Unconventional Oil/Gas Recovery, 2nd Edition)
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25 pages, 21681 KiB  
Article
Corrosion Cracking Causes in 13Cr-110 Tubing in Oil and Gas Extraction and Transportation
by Kangkai Xu, Shuyi Xie, Jinheng Luo and Bohong Wang
Energies 2025, 18(4), 910; https://doi.org/10.3390/en18040910 - 13 Feb 2025
Viewed by 764
Abstract
With the continuous development of oil and gas fields, the demand for corrosion-resistant tubing is increasing, which is important for the safe exploitation of oil and gas energy. Due to its excellent CO2 corrosion resistance, 13Cr-110 martensitic stainless steel is widely used [...] Read more.
With the continuous development of oil and gas fields, the demand for corrosion-resistant tubing is increasing, which is important for the safe exploitation of oil and gas energy. Due to its excellent CO2 corrosion resistance, 13Cr-110 martensitic stainless steel is widely used in sour gas-containing oil fields in western China. This paper describes a case of stress corrosion cracking (SCC) in a 13Cr-110 serviced in an ultra-deep gas well. The failure mode of the tubing is brittle along the lattice fracture, and the cracks are generated because of nitrogen gas-lift production-enhancement activities during the service of the tubing, leading to corrosion damage zones and cracks in the 13Cr-110 material under the synergistic effect of oxygen and chloric acid-containing environments. During subsequent production, the tubing is subjected to tensile stresses and cracks expanded at the 13Cr-110 lattice boundaries due to reduced structural strength in the corrosion region. To address the corrosion sensitivity of 13Cr-110 in an oxygen environment, it is recommended that the oxygen content in the wellbore be strictly controlled and that antioxidant corrosion inhibitors be added. Full article
(This article belongs to the Special Issue Advances in the Development of Geoenergy: 2nd Edition)
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18 pages, 6347 KiB  
Article
Supercritical CO2 Injection-Induced Fracturing in Longmaxi Shales: A Laboratory Study
by Xiufeng Zhang, Xuehang Song, Xingyu Li, Shuyuan Liu, Jiangmei Wang, Junjie Wei and Min Zhang
Energies 2025, 18(4), 855; https://doi.org/10.3390/en18040855 - 12 Feb 2025
Cited by 1 | Viewed by 950
Abstract
Although supercritical CO2 (SC-CO2) fracturing has shown promise in oil and gas development with demonstrated potential, its application in shale gas extraction remains in its infancy globally. In this study, fracturing experiments were conducted with water, liquid CO2 (L-CO [...] Read more.
Although supercritical CO2 (SC-CO2) fracturing has shown promise in oil and gas development with demonstrated potential, its application in shale gas extraction remains in its infancy globally. In this study, fracturing experiments were conducted with water, liquid CO2 (L-CO2), and SC-CO2, as well as SC-CO2 at varying pump rates. The results reveal that SC-CO2 fracturing produces a highly complex fracture network characterized by fractures of varying numbers, deflection angles, and tortuosity. Analysis of CO2 temperature and pressure data showed a sharp drop in injection pressure and temperature at breakdown, followed by fluctuations until injection stopped. Acoustic emission (AE) monitoring demonstrated that energy released during main fracture initiation significantly exceeded that from CO2 phase transition-driven fracture extension, underscoring the dominant role of main fractures in energy dissipation. Compared to hydraulic fracturing, SC-CO2 fracturing created a seepage area 2.2 times larger while reducing the breakdown pressure by 37.2%, indicating superior stimulation performance. These findings emphasize the potential of SC-CO2 to form intricate fracture networks, offering a promising approach for efficient shale gas extraction. Full article
(This article belongs to the Special Issue The Technology of Oil and Gas Production with Low Energy Consumption)
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