Geofluids最新文献

Lost circulation is a prominent issue when drilling in fractured formations, posing challenges for management and presenting a high risk of recurrence. Existing studies have primarily focused on predicting lost circulation pressure and location, which limits their effectiveness in guiding prevention and control efforts. Effective prevention and control of lost circulation requires a clear understanding of the underlying mechanisms in multiscale fractured formations and the identification of the dominant lost circulation channels. In this study, a dynamic lost circulation model incorporating multiple fractures was developed using the finite element method to investigate the lost circulation mechanism and dominant channels. Simulation results indicate that fracture length and fracture aperture have a significant influence on lost circulation, whereas fracture orientation and inclination exhibit negligible effects. When fractures in the formation are less than 500 μm in aperture, those greater than 200 μm serve as dominant lost circulation channels. No dominant channels are observed when the fractures in the formation either range from 500 to 1000 μm or exceed 1 mm. When fractures in the formation span from the micrometer to millimeter scale, those greater than 300 μm serve as dominant lost circulation channels. These findings provide valuable guidance for lost circulation prevention and control.

Unconventional tight/shale gas reservoirs have gained significant attention in the energy sector. The importance of temperature and pressure in shale imbibition lies in their profound influence on the kinetics, rate, and ultimate amount of water uptake, which directly impacts the efficiency of gas production. Given the importance of imbibition in influencing initial production, existing studies have primarily focused on shallow and mid-deep shale samples under limited pressure and temperature conditions, while the imbibition characteristics of shale formations deeper than 3500 m have not been thoroughly investigated. To this end, we apply low-field nuclear magnetic resonance (NMR) Carr–Purcell–Meiboom–Gill (CPMG) measurements to investigate the characteristics of water imbibition in shale under various pressure and temperature conditions. Very limited imbibition quantity was observed under spontaneous imbibition, while pressure significantly increased the imbibition amount by approximately eightfold at 30 MPa. Raising the temperature from room condition to 60°C significantly accelerated the imbibition rate, reducing the equilibrium time to 1 h. Samples with higher clay mineral content were found to exhibit greater imbibition amounts and faster imbibition rates.

The equivalent dry rock modulus serves as an important parameter in the construction of equivalent rock physical models. Moreover, it is the key information for accurately predicting the elastic parameters and longitudinal and transverse wave velocities of hydrocarbon reservoirs. The dry rock modulus of a formation is frequently hard to determine. Conventional rock physics modeling approaches are unreliable because of inaccurate input mineral modulus parameters and intricate compositional information. In this paper, a method based on the combination of two types of critical porosity models is proposed to obtain the effective dry rock modulus of rocks by constrained inversion of the critical porosity model. The method constrains the rock physical modeling process from the perspective of geologic diagenesis through the theoretical framework of rock physics, which reduces the unreliability of the required parameter inputs for rock physics and proves the reliability and greater applicability of the method.

To investigate the creep behavior of deep-buried hard rocks under various initial damage conditions, standard dolomite specimens were subjected to conventional triaxial compression and creep tests under a confining pressure of 30 MPa. The study analyzed the axial creep characteristics, total creep duration, deformation modulus, and failure modes of dolomite with different initial damage levels. Subsequently, a novel nonlinear creep constitutive model for hard rocks that incorporates initial damage was developed. The findings are as follows: (1) Under incremental loading, the axial strain of dolomite with varying initial damage exhibited a stepwise increase. The axial instantaneous strain increased nearly linearly with stress levels, and this strain intensified with greater damage at equivalent stress levels. (2) Dolomites with varying degrees of damage all experienced four distinct phases: instantaneous deformation, decelerating creep, steady-state creep, and accelerating creep. Increased damage corresponded to shorter total creep durations and reduced deformation moduli. At a loading stress of 80%, the total creep duration and deformation modulus of the damaged specimens decreased by 50.39% and 24.18%, respectively. (3) The creep failure mode of dolomite shifted from a predominant shear failure to a more complex combination of shear and tensile failure as damage increased. (4) This model accurately captures the three characteristic creep stages and the influence of initial damage on creep failure stress, offering a fresh perspective for the study of triaxial creep mechanical properties of dolomite with different initial damage levels under high-stress conditions.

Underwater implosion is typically accompanied by intense shock wave energy. The investigation of its energy release mechanism is crucial for structural safety protection, marine environmental monitoring, ocean acoustic field analysis, and energy utilization. This study systematically examines the underwater implosion behavior of structures with different shapes and constraint states based on computational fluid dynamics (CFD) simulation. Realistic water conditions such as compressibility, viscosity, and turbulence are considered for simulation reliability guarantee. Various aspects are analyzed including collapse time, shock wave amplitude, and energy radiation directionality. The simulation results indicate that the implosion pulse amplitude increases with the initial size, approximately following a power-law relationship, for spherical and cylindrical structures, either constrained or unconstrained. The implosion shock wave amplitude is sensitively affected by the internal air pressure of the structure. However, the fitting trend between structural size and pulse amplitude is almost comparable. In terms of energy radiation, different from the isotropic radiation pattern of spherical structures, cylindrical structures exhibit distinct directional energy radiation characteristic and vary with size and constraint conditions, attributed to variations in vorticity and pressure gradients, which modulate fluid velocity distribution. This study explores the implosion dynamics under different structural and constraint conditions, providing insights for analyzing implosion origin based on observations and advancing the utilization of implosion energy.

The insertion ratio of the diaphragm wall is crucial for the deformation control of the deep excavation of a subway station in water-rich soft soils. Taking the deep excavation project of a subway station in water-rich soft soils as the background, a flow–stress coupling finite element analysis model is established to describe the combined effect of deep excavation and dewatering based on the Biot consolidation theory. The general characteristics of the coupling deformation of dewatering and excavation are studied, and the influence of the insertion ratio of the diaphragm wall on the ground deformation is analyzed. The results show that (1) both dewatering and deep excavation can cause lateral displacement of the diaphragm wall toward the pit, and the dewatering-induced settlement dominates the total settlement, as compared with that induced by excavation. (2) With the increase of the insertion ratio of the diaphragm wall, the maximum lateral displacement of the diaphragm wall under excavation gradually decreases until it converges to a constant, while the maximum lateral displacement under dewatering and excavation decreases first and then increases. (3) The relationship between the maximum ground settlement and the insertion ratio of the diaphragm wall shows a similar development trend to that between the lowest dewatering head and the insertion ratio of the diaphragm wall, which is approximately linear when the insertion ratio of the diaphragm wall is between 1.1 and 2.3. The control of hydraulic head outside the pit by the diaphragm wall is an effective way to reduce the ground settlement, which has a positive effect on reducing the construction risk and cost in water-rich soft soils.

A novel method of groundwater immersion evaluation was proposed to better evaluate the range of groundwater immersion caused by the change of reservoir level, addressing the challenges of complex groundwater flow conditions in interfluvial areas and the low prediction accuracy of groundwater immersion. Through field investigation and theoretical analysis, we integrated crop root depth, building foundation depth, and capillary rise into the groundwater modeling, thereby establishing a conceptual model of groundwater flow for the study area. A detailed numerical simulation based on GMS was carried out to analyze the critical depth of groundwater in crops and building foundations and to evaluate the influence range and severity of groundwater immersion under three different water level conditions. Based on the classification of surface water in the interfluvial areas, along with computational results of groundwater levels and inundation area, a multivariate regression analysis was conducted to establish the relationship between different surface water levels and the degree of inundation. The results show that under flood water level conditions, the contour values of groundwater immersion are significantly higher than those under normal water levels. When the surface water level rises to the flood level, the proportion of severe immersion area reached 87% of the total study area. Due to high hydraulic head pressure and strong seepage capacity, crops in low-lying areas with developed root systems are more susceptible to groundwater immersion. Furthermore, the severity of immersion in severely affected areas exhibited a positive correlation with water levels. When the surface water level rose to 15.79 m, the severity of farmland disasters in the study area escalated significantly. The affected farmland accounted for 53.8% of the total study area, with lightly affected immersion zones comprising 17.3%. The research results can provide an important basis for the design, application, and follow-up research of water conservancy and hydropower projects.

Vulnerability is a key concept in flood hazard studies, especially concerning the damage to people, infrastructure, and housing. This article focuses on reducing housing vulnerability not only by managing floods at their source but also by introducing flood-adaptive housing design, such as flood chambers and spatial planning that avoids high-risk zones. Global challenges in housing stability during floods reveal shortcomings in flood management planning, particularly in the mountainous regions of the Danube basin (Austria) and the Karun and Karkheh basins (Iran). These areas demonstrate the need for improved integration of meteorological, hydrological, ecological, and geomorphological knowledge in planning, alongside better use of floodwaters in water-scarce regions. This study uses observational and case study methods, supported by over 20 years of empirical research and comparative data from the 2019–2022 floods in Iran and Austria. The research draws on six fields—meteorology, hydrology, ecology, geomorphology, hazard studies, and housing design—to propose a more integrated, process-based flood management model. The paper addresses three main aspects: (1) evaluating current scientific methods for reducing flood risk, (2) introducing geomorphic indicators to enhance flood data used in housing design, and (3) proposing housing concepts that absorb and utilize floods rather than resist them. A brief comparative validation highlights housing performance before and after adaptive measures were implemented. The result is a scientific guide map: a cross-disciplinary framework for sustainable housing design that incorporates flood chambers and better floodplain use. It offers a complementary strategy to traditional hydrological approaches, aimed at reducing flood damage and strengthen local freshwater resources.

Carbonate rocks exhibit complex pore structures composed of matrix pores, vugs, and fractures, which result in non-Archie behavior in resistivity measurements and present significant challenges for reservoir evaluation. The rapid advancement of digital rock physics offers new approaches to address the complexities in saturation assessment of carbonate reservoirs. In this study, digital rock models of matrix pores, vugs, and fractures were constructed using computed tomography scans and stochastic functions. Finite element simulations were performed to visualize current flow within the pore structures and to quantify the respective contributions of conductive structures to overall resistivity. The results show that matrix pores generally conform to Archie’s law, fractures act as efficient parallel channels, and vugs behave as series-connected elements with surrounding pores. Based on these findings, a new conductivity and saturation model for fractured-vuggy carbonates was established by representing the conductive structures with a mixed series–parallel configuration. Compared to the conventional Archie equation, the new model improved saturation prediction accuracy by 8.50% and demonstrated strong applicability in field applications. This study provides direct visualization of the current flow and quantitative evaluation of conductive contributions from distinct pore structures and establishes relationships between saturation and petrophysical parameters, offering valuable guidance for the exploration of carbonate reservoirs.

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.