Geofluids最新文献

Amid growing global clean energy demand, coalbed methane (CBM) in the coal-rich Weizhou area holds great development value. This study explores Weizhou CBM′s geochemical traits and genesis via analyzing gas compositions (Shanxi and Taiyuan Formations), stable isotopic distributions (δ¹³C₁, δD, δ¹³CO₂, and δ¹⁵N), and their burial depth variations. Results show that CBM is hydrocarbon-dominated: Shanxi and Taiyuan Formations have average methane contents of 89.89% and 88.24%, respectively. Coal metamorphism is medium-to-high (R_o: 1.76%–2.52%, subbituminous to anthracite). Isotopic averages were as follows: Shanxi versus Taiyuan (δ¹³C₁: −36.91‰ vs. −36.68‰; δ¹³C₂: −19.46‰ vs. −24.2‰; and δ¹³CO₂: −17.56‰ vs. −15.29‰) and regional δD (−188.7‰) and δ¹⁵N (−1.27‰). Further, the results identify gas source differentiation between the Shanxi Formation and Taiyuan Formation, which is controlled by burial depth and coal metamorphism degree. A strong δ¹³C₁–δ¹³C₂ correlation (δ¹³C₁ = 0.5044 δ¹³C₂ − 26.188, R² = 0.616) confirms the dominant status of thermogenic gas. δ¹³C₁ − C₁/(C₂ + C₃) data fall in the secondary thermogenic zone, indicating modification by diffusion, migration, and fractionation. Gas source compositions differ between the upper Shanxi (0–4 seams) and the lower Taiyuan (5–20 seams) Formations. These findings support optimized Weizhou CBM exploration and utilization.

To elucidate the water–rock interaction mechanisms of the Julong Hot Springs in Changbai Mountain, this study first analyzed the leaching patterns of hydrochemical components in water–rock interactions. The PHREEQC software was then utilized to calculate mineral saturation indices and mineral phase diagrams, thereby exploring the thermodynamic equilibrium state of water–rock interactions. A mineral reaction kinetics model was constructed to investigate the reaction rates of rock minerals and quantify their kinetic processes. The results show that (1) within 72 h of reaction, Na⁺ is the predominant cation, and HCO₃⁻ is the predominant anion in both deionized water–rock interaction and geothermal water–rock interaction. The hydrochemical types are all HCO₃–Na. (2) In deionized water–rock interaction and geothermal water–rock interaction, albite, K-feldspar, and quartz are the main minerals that dissolve. In deionized water–rock interaction and geothermal water–rock interaction, the dissolution of albite and K-feldspar occurs in the gibbsite and kaolinite stages, respectively, and both processes occur in the early stages of the reactions. (3) In the deionized water–rock interaction, the dissolution and precipitation of albite, K-feldspar, and quartz conform to the transition state theory equation. During the model prediction process, the concentrations of Na⁺ and K⁺ exhibited a significant increase within the initial 180 days, after which the increase slowed and gradually stabilized. The absolute values of the molar changes in albite and K-feldspar exhibit complex variations, initially increasing, then decreasing, followed by another increase, and finally decreasing. The maximum molar changes of albite and K-feldspar were observed at 5 days, with respective values of −1.42e − 3 and −6.27e − 4 mol. The molar change of quartz initially increased and then decreased, reaching its maximum value of 4.26e − 4 mol at 60 days. By 540 days, the molar changes of minerals approached 0, indicating that the water–rock interaction had reached equilibrium.

Due to multiple dynamic disturbances caused by mining activities, the internal fractures in the surrounding rock of the roadway continue to expand, resulting in the continuous weakening of the mechanical properties of the sandstone. Based on the split Hopkinson pressure bar (SHPB) tests, this study investigates the dynamic mechanical properties of surrounding rock sandstone under repeated impact loading. Through experiments on the dynamic response of sandstone samples under different impact frequencies and strain rates, the strength degradation and toughness variation during repeated loading were analyzed. The experimental results indicate that as the number of impacts increases, the dynamic compressive strength and modulus of sandstone gradually decrease, exhibiting a pronounced weakening trend. Simultaneously, the failure mode of sandstone transitions from brittle failure in the initial stage to plastic deformation in the later stage, reflecting the gradual destruction and rearrangement of the material′s internal microstructure. The variation in strain rate significantly impacts the degree of weakening, with a more pronounced decline in sandstone strength under high strain rates. The findings reveal that energy dissipation increases significantly due to multiple impacts, suggesting that the long-term stability of sandstone materials under repeated loads warrants attention in practical engineering applications. This study provides experimental evidence for understanding the mechanical behavior of sandstone under dynamic loading conditions and serves as a valuable reference for related engineering design and safety assessments.

Accurate characterization of the feature parameters of lost circulation channels in fractured formations is of great significance for assessing lost circulation risk and designing effective leakage prevention and plugging strategies. To address the limitations of existing fracture characterization methods in capturing both the spatial distribution and internal structural features of fractures, a case study was conducted in an oilfield in China. Considering the combined influence of fracture density and fracture aperture on fracture development, a fracture development index analytical model was established based on R/S fractal theory. Furthermore, a digital characterization method for complex lost circulation channels was developed using the Monte Carlo modeling technique. Based on logging interpretation results, the fracture development indices of four intervals in a selected well were calculated and compared with the corresponding borehole imaging logs. The results show that higher fracture development index values correspond to more developed fractures in the imaging logs, thereby confirming the reliability of the proposed index model. By integrating the actual distribution of fracture parameters in the study area with the fracture development index model, a digital representation of fractures with varying degrees of development can be achieved, providing a more realistic basis for numerical simulation of complex lost circulation scenarios. The dynamic lost circulation numerical model indicates that, as the fracture development index increases, the lost circulation channels tend to connect along the maximum horizontal stress direction. The research findings offer theoretical guidance for risk prediction of lost circulation and optimization of leakage prevention and plugging strategies.

Unlike domestic carbonate reservoirs, overseas carbonate reservoirs typically exhibit significant lithological variations and stronger heterogeneity. There is a lack of effective methods for energy supply and techniques to enhance oil recovery. Additionally, acquiring data during offshore platform operations presents significant challenges. Evaluating field productivity solely based on existing data remains problematic. To address this, we integrate drill stem test (DST) data and reservoir numerical simulation to calculate productivity and conduct sensitivity analysis. Initially, the DST data are collected for pressure transient analysis to estimate reservoir permeability and skin factors, which enables reasonable single-well productivity predictions. Subsequently, detailed reservoir numerical simulations are utilized to investigate the effects of liquid production rate, production pressure drop, horizontal section length, and perforation position on field productivity, thus guiding optimal production design. Results indicate that the combination of DST data and numerical simulations is essential for accurately assessing productivity in carbonate reservoirs and supporting efficient development. With an increasing liquid production rate, cumulative oil production gradually rises, plateauing when it exceeds 7%. As production pressure drop and horizontal section length increase, the recovery factor improves up to an optimal value. Improper perforation positions, either too low or high, reduce cumulative oil production and oil recovery.

The Midu Basin has a complex geological structure, active neotectonic movement, strong magmatic activity, and abundant geothermal resources, but the current research degree is low. Five representative hot springs in the Midu area were studied; the hydrochemistry and hydrogen and oxygen isotope characteristics of water samples were analyzed; and the recharge elevation, geothermal reservoir temperature, and circulation depth of hot springs were calculated. This study points out that the formation of hot springs is all under the joint action of the Red River Fault and the Xiangyun nappe structure based on hydrochemical characteristics, calculation results, and tectonic location features of hot springs. However, our study further reveals that their development in distinct segments of the nappe structure results in varying surrounding lithologies, which directly govern the intensity and pathways of water–rock interactions. Based on predominant cations in geothermal water, the five representative hot springs can be divided into two types: Na⁺ type and Ca²⁺ type. A genetic model of these hot springs is proposed for the first time, whereby they are heated by deep and large faults and recharged by faults and folds, elucidating the lithology–tectonics–fluid linkage in the nappe-related geothermal system of the region. The research results of this paper provide key data and theoretical support for geothermal research in the Midu area and also provide important guiding significance for geothermal research under the background of the same structure.

The scientific understanding of the evolution of limestone structure under the combined action of freeze–thaw cycles (F-T cycles) and hydrochemical solutions is of great significance for revealing the mechanism of frost damage generation in cold limestone areas. In this study, 60 cycles of freeze–thaw experiments were conducted on limestone under the pH values of 4, 7, and 9, respectively. Mass loss rate, permeability, and fractal dimension of microstructure were used as parameters to evaluate the evolution of limestone structure, and the evolution patterns of limestone structure under the combined action of different chemical solutions and F-T cycles were investigated. The results show that temperature is the fundamental factor controlling the structural evolution of limestone samples, with physical effects dominating below 0°C and chemical effects dominating above 0°C. Mass loss gradually develops from the surface to the interior of the rock and is caused by the peeling of surface particles in the initial five F-T cycles. The difference in mass loss rate is not significant under different acid–base environments. Physical effects generated microcracks on the surface and extended into the interior of the specimens, enhancing permeability and fractal dimension. The influence of chemical effects gradually manifested after 5–10 F-T cycles, causing the fracture volume to expand, improving permeability, and changing the mass loss rate. The dissolution effect of the acidic solution on calcite had the greatest impact on microstructure. Due to differences in chemical effects intensity, the degree of structural change in limestone after 60 F-T cycles was in the order of acidic environment > alkaline environment > neutral environment. The current results could contribute to a deeper understanding of the mechanism of limestone strength degradation in cold regions.

In engineering practice, the accuracy of slope stability assessment significantly influences personal and property safety; therefore, accurate prediction of slope stability is of critical importance. Because of the strong nonlinear prediction capacity of machine learning, a particle swarm optimization–based random forest (PSO-RF) algorithm model was constructed to achieve the classification prediction of slope stability. A dataset comprising 859 slope case samples was compiled. The unit weight, cohesion, internal friction angle, slope angle, slope height, and pore pressure ratio were taken as the input parameters of the model, while the slope stability was taken as an output parameter. In addition, the relative importance indicators of each characteristic value were computed. For the purpose of evaluating the predictive performance of the PSO-RF model, a confusion matrix was constructed, and six indicators, namely, specificity, accuracy, precision, recall, F1 score, and area under the curve (AUC), were calculated. In addition, the predictive outcomes generated by this model were contrasted with those of other machine learning models. The results demonstrated that the PSO-RF model achieved the highest predictive performance, with its accuracy, precision, recall, specificity, and F1 score all exceeding 90%, and the AUC was higher than 0.96, indicating that the PSO-RF was able to accurately predict slope stability. The results of the engineering application showed that the predicted results of the PSO-RF are basically consistent with the actual state of the engineering slope. The internal friction angle exerted the most significant impact on the prediction outcomes, with a relative importance indicator of 3.896. This study investigates the applicability of machine learning in the field of slope stability assessment. It offers an innovative method for forecasting slope stability and holds substantial importance in disaster prevention and mitigation efforts.

Double porosity model differentiates fluid pressure between contact of grains (COG) and the main pore space. This study is motivated by determining phase velocity (V_ps) and the quality factor (Q_ps) of slow P-wave for double porosity rock. The trick is the use of the compressibility matrices calibrated from (ultrasonic) fast P-wave data. Berea sandstone saturated with water is used for illustration. Double porosity models (with the real Darcy permeability k_D and assumed-zero k_D) are both capable of well regenerating the phase velocity (V_p) and quality factor (Q_p) of fast P-wave ultrasonically measured on the sandstone. However, the two double porosity models yield considerably different Q_p at frequencies exceeding 10⁷ Hz. In addition, Biot theory is used as a single porosity model for the calculation of V_ps and Q_ps. It is found that the double porosity model with the real k_D is substantially different from the single porosity model in the resulting V_ps at high frequencies. The results show that the behavior of slow P-wave at frequencies higher than 10⁵ Hz is governed by the double porosity model rather than the single porosity model.

The purpose of this paper is to analyze the diffusion mechanism of polymer slurry in rough fractures under slurry–rock coupling, which has important practical significance for polymer grouting repair of rock fractures. The rock mass fracture with random roughness is constructed in the spatial frequency domain, and the random rough fracture slurry diffusion model is established; then, a model experiment is established to verify the accuracy of the numerical method. Finally, the fluid–solid coupling diffusion mechanism in the grouting process is analyzed. The results show that (1) the maximum flow rate of slurry increases with the increase of overall roughness. The coarser the fracture, the more irregular the velocity distribution along the fracture opening direction. (2) The stress in rough fractures gradually decreases with the direction of slurry diffusion. The rougher the fracture, the greater the stress fluctuation, the more phenomena of stress concentration appear at the tip. (3) The stress field is greatly influenced by the shape of fractures, in depressed areas, where stress mutations can easily lead to plastic damage and secondary fractures.