Geofluids最新文献

The study used an integrated method of water quality indices (WQIs) and multivariate statistical analysis to evaluate the hydrogeochemical characteristics of groundwater samples and their appropriateness for drinking and agricultural applications in Kombolcha City. The hydrogeochemical parameters from 17 water samples were examined using standard methods. The WQI, irrigation indices, and geographical information systems (GISs) were used to determine groundwater suitability for various purposes and the spatial distribution of major ions. The study also utilized multivariate statistical methods, including principal component analysis (PCA) and cluster analysis (CA), to evaluate complex groundwater quality datasets. The results revealed that all hydrogeochemical characteristics were in line with Ethiopian drinking water standards and WHO drinking water guidelines. The WQI indicates that 94% of the samples are in excellent condition, whereas about 6% are in acceptable drinking water conditions in the study area’s southern and central regions with considerable agricultural and industrial activities. The Ca²⁺-HCO₃⁻ facies comprise about 53% of the shallow aquifer, and the remaining samples are found in the Ca²⁺-Mg²⁺-Cl⁻ and Ca²⁺-Na⁺-HCO₃⁻–type facies. SAR, Na%, PI, and MAR indicators showed that most water samples are very good to moderately suitable for agricultural use. CA uses dendrogram plots to group groundwater characteristics and sample locations into three groups based on common groundwater features. The study concluded that the combination of WQI, multivariate statistical, and GIS is a viable approach for prioritizing groundwater mitigation and monitoring efforts in Ethiopia’s semiarid regions of the Awash River basin.

Low-permeability sandstone reservoirs, as a subset of unconventional oil and gas reservoirs, have gained significant attention due to their distinct exploration and development potential. These reservoirs exhibit intricate heterogeneity, variable seepage behaviors, and complex remaining oil distribution. As a result, comprehensive research is crucial to optimize exploration and development activities. In this study, we focused on the Chang 6 reservoir in Jiyuan Oilfield, Ordos Basin—a representative low-porosity and low-permeability reservoir. We delved into the pore-throat structure and seepage mechanisms of various flow units, which are characterized as spatially continuous reservoir segments with uniform petrophysical properties and consistent seepage dynamics. These investigations are critical for improving reservoir characterization, pinpointing the distribution of remaining oil, and forecasting reservoir development and production outcomes. This study integrated several methods, including nuclear magnetic resonance experiments, constant-rate mercury intrusion, high-pressure mercury intrusion, image particle sizing, scanning electron microscopy, and pore-casted thin sections. Our results indicate that different flow units adhere to unique dynamic fluid occurrence patterns. To evaluate the flow units of the Chang 6 member reservoir in the Jiyuan Oilfield, we considered five parameters: sand thickness, porosity, permeability, oil saturation, and flow zone index. Based on microscopic pore structure characteristics and their influence on movable fluid saturation, we classified flow units into four types: excellent (E), good (G), moderate (M), and poor (P). We observed that the microscopic pore structures among these four flow unit types differ considerably, which in turn affects the states of the movable fluids within them. There is a weaker correlation between the pore-throat radius ratio and the movable fluid saturation in reservoirs (R² = 0.4047), whereas there is a stronger correlation between movable fluid saturation and throat radius (R² = 0.8434). Notably, the throat radius distribution and the main-flow throat radius emerged as key determinants. During the exploration and development stages, Type E and Type G flow units showed the most promising production potential. As a result, it is imperative to craft development strategies that align with the microscopic pore structures unique to each flow unit.

The Wuqi area of the Ordos Basin boasts significant resource potential in the Chang 8 member of the Yanchang Formation. However, under the dual control of lithology and physical properties, reservoirs are generally dense and heterogeneous, and the quality of the oil layer changes rapidly, which brings difficulties to the optimization of favorable areas. To evaluate the reservoir quality more accurately, based on core observations, and logging and dynamic data analysis, combined with casting thin sections, scanning electron microscopy, high-pressure mercury injection, nuclear magnetic resonance, and other related experiments, different reservoir types and characteristics were analyzed, and a comprehensive method for evaluating the reservoir quality was established. There are three types of sand body structures in the shallow-water delta of Chang 8 in the study area, including the continuous superposition type, interval superposition type, and lateral single-layer type. They mainly experienced diagenesis, such as compaction, cementation, and dissolution. Among these, porosity loss in the Chang 8 reservoir due to compaction and cementation reached 79.3%, consistent with trends observed in other continental tight oil plays such as the Songliao and Junggar Basins, while the improvement in physical properties due to dissolution was minimal. The main parameters influencing different reservoir types are optimized, and the comprehensive classification with the multivariate coefficient is constructed after providing coefficients with different weights. Four reservoir types are quantitatively delineated, among which the physical properties of Type I reservoirs are the best and the physical properties of Type IV reservoirs are the worst. Combined with the difference in the characteristics of sensitive logging curve responses, four logging parameters, density, neutron, resistivity, and acoustic time difference, are optimized, and different reservoir types are quantitatively identified by Fisher discriminant analysis. Comprehensively considering the change in the vertical sand body structure and reservoir type, the three key parameters of interlayer density, interlayer frequency, and reservoir thickness are selected, and the comprehensive evaluation index N of reservoir quality is innovatively constructed. The proposed evaluation index effectively decouples lithological and petrophysical variations, refining reservoir quality assessments for enhanced exploration and production strategies. The greater the N value is, the better the quality of the oil layer. The smaller the N value is, the thinner the oil layer, the more developed the interlayer, and the worse the oil layer quality. The N index exhibits a strong correlation with production characteristics, indicating that the method has effectively evaluated reservoir quality and provided a theoretical basis for targeting favorable areas.

For the suspension bridge construction located at the site of high seismic intensity, the stability of the anchorage foundation under the seismic load considerably affects the safety of the suspension bridge. Based on a suspension bridge case in southwest China, this study investigated the occurrence of earthquakes in this area and synthesized the artificially designed seismic waves that meet the requirements of the specification. Simultaneously, the FLAC3D numerical model was established, and the dynamic stability of the gravity anchorage foundation system under artificially designed seismic waves was analyzed. The results indicated that under the seismic load, the anchorage foundation system was globally stable, and small sliding and shear damage could be observed on the surface of rock strata. With the seismic load and dry–wet cycles combined, the anchorage foundation’s horizontal displacement and vertical settlement increased, the horizontal displacement was nearly doubled, and the shear plastic zone was enlarged. The grouting reinforcement could strengthen the connection between the anchorage and the surrounding rock strata, reducing the surrounding rock strata’s dynamic shear strain, particularly from 6 × 10⁻³ to 2.5 × 10⁻⁴ at the midsection of the slope. The safety factor at the base of the foundation pit fluctuated around 1.0 before reinforcement, increasing to greater than 2.5 after reinforcement.

Acid fracturing is currently employed to develop the carbonate gas reservoir in the second section of the Dengying Formation at the Anyue Gas Field, Sichuan Basin. However, improper acid-fracturing operational parameters pose a risk of fracture communication with the bottom water layer, leading to increased water production and a significant decline in gas productivity. In this study, numerical simulations were performed using FracPro PT software, taking into account the geological characteristics of the second section of the Dengying Formation. The analysis considered various in situ stress profiles and different vertical distances to the bottom water layer (H_w) to explore effective strategies for controlling fracture height during acid treatment. The results indicate that injection volume, injection rate, permeability, stress difference between the reservoir and the barrier (Δσ), and acid viscosity are the key factors affecting fracture height growth. When the reservoir stress is 4 MPa higher than that of the barrier and H_w is less than 70 m, it is recommended to construct an artificial barrier above the bottom water layer to increase Δσ by 4.0 to 5.0 MPa and to inject 160 m³ of gelled acid at a rate of 5.0 to 6.0 m³/min to prevent fracture communication with the bottom water layer. Conversely, when reservoir stress is 4 MPa lower than the barrier and the vertical distance H_w is greater than 50 m, over 200 m³ of gelled acid can be injected at a rate exceeding 6.0 m³/min to achieve the largest stimulated reservoir volume due to effective containment by the barriers. Furthermore, when the stress gradient is positive (e.g., 113–115–117 MPa) and H_w exceeds 30 m, more than 200 m³ of gelled acid can be injected at a rate greater than 7.0 m³/min, benefiting from the barrier effect of the lower layer. On the other hand, for a negative stress gradient (e.g., 117–115–113 MPa) and H_w less than 50 m, an artificial barrier must be established to increase Δσ by at least 6.0 MPa. In this scenario, a limited acid volume of 120 m³ is recommended, injected at a rate of 7.0 to 8.0 m³/min to avoid excessive fracture height growth reaching the bottom water layer. Based on the optimal acid treatment strategy for controlling fracture height, a field application was carried out at the Gaoshi-X well. The initial daily production rate reached 17.6 × 10⁴ m³/day and subsequently stabilized at 13.5 × 10⁴ m³/day, achieving both high and stable production. The conclusions drawn from this study aim to provide theoretical guidance for optimizing acid-fracturing designs in carbonate gas reservoirs with bottom water, ultimately enhancing production effectiveness while mitigating associated risks.

Oil production prediction is crucial for the formulation of adjustment strategies, enhancement of recovery rates, and guidance of production in oilfields. Traditional production prediction methods based on reservoir numerical simulation are costly, challenging, and heavily influenced by human experience, while the application of production prediction models such as decline curves yields poor results. To achieve rapid, low-cost, and intelligent oil production prediction, we propose a multi-input deep neural network model combining convolutional neural networks (CNNs) and long short-term memory (LSTM) networks with an attention mechanism. This model achieves prediction through two primary input paths: firstly, utilizing CNN to extract spatial dynamic features between wells to capture interwell production relationships and secondly, employing LSTM to extract temporal dynamic features of the oilfield. The model combines the attention mechanism to strengthen the key information. Additionally, to quantify the impact of different input features on production, we adopt a random forest algorithm to assess feature importance and optimize data input through assigned weights. Finally, the trained model is used to forecast oilfield production. Three sets of comparative experiments are conducted in this paper. Experiment 1 confirms that the new method outperforms previous methods in prediction performance. Experiment 2 demonstrates that the multi-input model exhibits superior prediction performance compared to single-input models. Experiment 3 verifies that the combination of importance weight initialization and the attention mechanism significantly enhances the accuracy of the model’s predictions.

Injecting air or CO₂ into shale reservoirs can significantly enhance oil recovery (EOR) following the initial depletion. However, effectively characterizing the complex pore structure of shale reservoirs poses a challenge, leading to an incomplete understanding of the seepage mechanism and microscopic production characteristics of air/CO₂ flooding at different pore scales. In this study, we characterized the microscopic pore structure of shale reservoirs through the reconstruction of visual and quantitative digital cores in multiple dimensions. Subsequently, the online nuclear magnetic resonance (NMR) air/CO₂ flooding experiments were conducted, and the production characteristics and influencing factors of microscopic pore crude oil were quantitatively studied. The results show that the pore structure characteristics and connectivity of shale reservoirs are highly intricate and the deterioration of reservoir physical properties correlates with a decreasing trend in pore-throat coordination numbers and heterogeneity. Shale oil primarily occurs in three types of pores (< 0.1, 0.1–1, and 1–10 μm), and improving micronanopore recovery is urgent for EOR. Crude oil production is observed during the air and oil molecule generation low-temperature oxidation (LTO) reaction. Additionally, CO₂ accelerates mass transfer and oil and gas extraction through molecular diffusion effects, substantially improving shale oil recovery; however, significant differences exist in the microscopic production characteristics of air/CO₂ flooding. High-oxygen-concentration air flooding or high-pressure CO₂ proves beneficial for EOR, especially for small pores and macropores, which contribute 45.75%–53.42% recovery. This study provides scientific and theoretical support for clarifying the microscopic production characteristics and efficient development of shale oil.

The blasting at a site can cause impact disturbances to an open-pit mine slope. For further study the dynamic mechanical properties of rock masses in open-pit mine slope, in this paper, the mudstone of an open-pit slope in Inner Mongolia Autonomous Region of China was taken as research object. Through an indoor split-Hopkinson impact test and a finite difference method and discrete element method coupling simulation (FDM-DEM), the macro and micro impact mechanical response of mudstone under different impact velocities was studied. The results showed that under dynamic load, mudstone exhibited significant strain rate effects. The postpeak plasticity varied in exponentially increasing changes. The crack propagation process in mudstone can be divided into undamaged, initiation, propagation, and rupture stages. As the impact velocity increased, the initiation stage exhibited more microcracks, and the cracks opening in the rupture stage became larger. The 3D coupling numerical model can satisfy stress effectiveness during the dynamic impact process. During the impact process, microcracks increased sharply before the peak stress, and there was a strain lag between the maximum point of crack increment and the peak point of stress. A large number of internal microcracks developed during the postpeak stage, and the cumulative crack increment exhibited a reverse “Z” shape.

Taking the Guodishan Fault as an example, the regional geological evolution background and measured gas parameters were analyzed, and the gas occurrence characteristics in the region and the control effect of synsedimentary faults on regional gas were studied. Research has shown that the gas occurrence in the control area of the Guodishan Fault is complex and has obvious zoning characteristics, and its syndepositional characteristics and geological movements have a significant impact on the generation and preservation of coal gas. The gas content and pressure in the area controlled by the fault gradually weaken from the severely affected areas of the hanging wall to the footwall, then to the moderately and weakly affected areas of the hanging wall. Warning values for coal and gas outburst are reached at the burial depths of 285, 420, 577, and 1717 m, respectively. It is worth noting that gas anomalies frequently occur in the moderately affected areas, so coal and gas outburst may occur above the warning burial depth.

It is one of the important disasters faced by coal mine that roof energy accumulation leads to its advance failure and roadway failure. Identifying the position of roof energy accumulation can predict the position of roof advance failure and roadway deformation, so as to take preventive measures. Based on two generalized displacement beams, the accumulation law of the bending moment and energy density of the top coal wall under different loads, different thicknesses, and different cantilever lengths is investigated. The following conclusions are drawn: (1) Under different load conditions, the peak of the bending moment and energy density both appear at 10 m in front of the coal wall and rapidly decrease to 0 after reaching the peak and no longer change. The peak value of the bending moment increases linearly with the increase of the load, and the relation is M = −143.32q − 286.63. The peak value of bending moment changes exponentially with the increase of load, and the relation is U^e = 200.46e^0.42q. (2) Under different thicknesses, the bending moment of the thickness to the rock layer has an irregular distribution at the peak value. When the thickness is 12.5 and 15 m, the change tends to be consistent, and when the thickness is 7.5 and 10 m, the bending moment of the roof is small when the thickness is 17.5 m. When the thickness is less than 17.5 m, the smaller the thickness is, the larger the peak value is, and the more advanced the peak value is. The smaller the thickness of the roof, the smaller the range of energy density accumulation. (3) Under different cantilever lengths, with the increase of cantilever length, the peak bending moment presents a linear increase, and the relationship is M^e = −158.22 L + 137.4, and the range of bending moment accumulation increases with the increase of the roof cantilever length. With the increase of the cantilever length, the peak energy density of the roof increases exponentially, and the relationship is U^e = 3.5536e^1.1067L, and the lead energy accumulation distance of the roof increases. (4) When the thickness of the roof is 10 m, the stress peak occurs more frequently within 5–15 m in front of the working face, which well confirms the correctness of the theoretical analysis.