Search Results (21)

Chinese coalbed methane (CBM) reservoirs exhibit characteristically low recovery rates due to adsorbed gas dominance and “three-low” properties (low permeability, low pressure, and low saturation). CO₂ thermal drive (CTD) technology addresses this challenge by leveraging dual mechanisms—thermal desorption and displacement to enhance production; however, its effectiveness necessitates uniform fracture networks for temperature field homogeneity—a requirement unmet by conventional long-fracture fracturing. To bridge this gap, a coupled seepage–heat–stress–fracture model was developed, and the temperature field evolution during CTD in coal under non-uniform fracture networks was determined. Integrating multi-cluster fracture propagation with stress barrier and intra-stage stress differential characteristics, a stress-barrier-responsive diverting fracturing technology meeting CTD requirements was established. Results demonstrate that high in situ stress and significant stress differentials induce asymmetric fracture propagation, generating detrimental CO₂ channeling pathways and localized temperature cold islands that drastically reduce CTD efficiency. Further examination of multi-cluster fracture dynamics identifies stress shadow effects and intra-stage stress differentials as primary controlling factors. To overcome these constraints, an innovative fracture network uniformity control technique is proposed, leveraging synergistic interactions between diverting parameters and stress barriers through precise particle size gradation (16–18 mm targeting toe obstruction versus 19–21 mm sealing heel), optimized pumping displacements modulation (6 m³/min enhancing heel efficiency contrasted with 10 m³/min improving toe coverage), and calibrated diverting concentrations (34.6–46.2% ensuring uniform cluster intake). This methodology incorporates dynamic intra-stage adjustments where large-particle/low-rate combinations suppress toe flow in heel-dominant high-stress zones, small-particle/high-rate approaches control heel migration in toe-dominant high-stress zones, and elevated concentrations (57.7–69.2%) activate mid-cluster fractures in central high-stress zones—collectively establishing a tailored framework that facilitates precise flow regulation, enhances thermal conformance, and achieves dual thermal conduction and adsorption displacement objectives for CTD applications. Full article

The dynamic process of water depletion plays a critical role in both surface coalbed methane (CBM) development and underground gas extraction, reshaping water–rock interactions and inducing complex permeability responses. Addressing the limited understanding of the coupling mechanism between heterogeneous pore water evolution and permeability during dynamic processes, this study simulates reservoir transitions across four zones (prospective planning, production preparation, active production, and mining-affected zones) via centrifugal experiments. The results reveal a pronounced scale dependence in pore water distribution. During low-pressure stages (0–0.54 MPa), rapid drainage from fractures and seepage pores leads to a ~12% reduction in total water content. In contrast, high-pressure stages (0.54–3.83 MPa) promote water retention in adsorption pores, with their relative contribution rising to 95.8%, forming a dual-structure of macropore drainage and micropore retention. Multifractal analysis indicates a dual-mode evolution of movable pore space. Under low centrifugal pressure, D₋₁₀ and Δα decrease by approximately 34% and 36%, respectively, reflecting improved connectivity within large-pore networks. At high centrifugal pressure, an ~8% increase in D₀−D₂ suggests that pore-scale heterogeneity in adsorption pores inhibits further seepage. A quantitative coupling model establishes a quadratic relationship between fractal parameters and permeability, illustrating that permeability enhancement results from the combined effects of pore volume expansion and structural homogenization. As water saturation decreases from 1.0 to 0.64, permeability increases by more than 3.5 times. These findings offer theoretical insights into optimizing seepage pathways and improving gas recovery efficiency in dynamically evolving reservoirs. Full article

Coal seam floor water inrush is one of the most significant hazards affecting the safety of coal mine operations. To prevent water inrush incidents, it is critical to investigate the evolution of fault characteristics during the mining of working faces. This study takes the 4104 working face of the Heshan mine in China as the engineering case, and a fluid–solid–damage coupling numerical model of the mining process is established. COMSOL multiphysics software is employed to analyze the evolution of fault characteristics in the coal seam floor under mining-induced disturbances. The results show that under mining disturbances, the stress on the fault plane decreases initially and then increases, with higher stress at the sides and lower stress in the center. These stress variations induce alternating states of sliding and stability on the fault plane, indicating that fault reactivation manifests as a dynamic, non-equilibrium process. As the rock mass gradually deteriorates, the stress field at the fault zone undergoes redistribution, leading to fault reactivation. This process further exacerbates damage to the rock mass, resulting in a continuous increase in the permeability coefficient within the fault zone, thereby elevating the probability of water inrush hazards. Areas with more severe damage typically exhibit higher permeability, forming high-risk zones for water inrush. This study explores the characteristics of fault reactivation and its relationship with the seepage field, providing a theoretical basis for coal mining enterprises to prevent and control fault-induced water inrush. Full article

Understanding the coupled evolution mechanisms of stress, fracture, and seepage fields in overburden strata is critical for preventing water inrush disasters during fully mechanized mining in deep coal seams, particularly under complex hydrogeological conditions. To address this challenge, this study integrates laboratory experiments with FLAC3D numerical simulations to systematically investigate the multi-field coupling behavior in the Luotuoshan coal mine. Three types of coal rock samples—raw coal/rock (bending subsidence zone), fractured coal/rock (fracture zone), and broken rock (caved zone)—were subjected to triaxial permeability tests under varying stress conditions. The experimental results quantitatively revealed distinct permeability evolution patterns: the fractured samples exhibited a 23–48 × higher initial permeability (28.03 mD for coal, 13.54 mD for rock) than the intact samples (0.50 mD for coal, 0.21 mD for rock), while the broken rock showed exponential permeability decay (120.32 mD to 23.72 mD) under compaction. A dynamic permeability updating algorithm was developed using FISH scripting language, embedding stress-dependent permeability models (R² > 0.99) into FLAC3D to enable real-time coupling of stress–fracture–seepage fields during face advancement simulations. The key findings demonstrate four distinct evolutionary stages of pore water pressure: (1) static equilibrium (0–100 m advance), (2) fracture expansion (120–200 m, 484% permeability surge), (3) seepage channel formation (200–300 m, 81.67 mD peak permeability), and (4) high-risk water inrush (300–400 m, 23.72 mD stabilized permeability). The simulated fracture zone height reached 55 m, directly connecting with the overlying sandstone aquifer (9 m thick, 1 MPa pressure), validating field-observed water inrush thresholds. This methodology provides a quantitative framework for predicting water-conducting fracture zone development and optimizing real-time water hazard prevention strategies in similar deep mining conditions. Full article

As the development of oilfields in China enters its middle-to-late stage, the old oilfields still occupy a dominant position in the production structure. The seepage process of reservoirs in the high Water Content Period (WCP) presents significant nonlinear and non-homogeneous evolution characteristics, and the traditional seepage-modeling methods are facing the double challenges of accuracy and adaptability when dealing with complex dynamic scenarios. In recent years, Deep Learning technology has gradually become an important tool for reservoir seepage field prediction by virtue of its powerful feature extraction and nonlinear modeling capabilities. This paper systematically reviews the development history of seepage field prediction methods and focuses on the typical models and application paths of Deep Learning in this field, including FeedForward Neural networks, Convolutional Neural Networks, temporal networks, Graphical Neural Networks, and Physical Information Neural Networks (PINNs). Key processes based on Deep Learning, such as feature engineering, network structure design, and physical constraint integration mechanisms, are further explored. Based on the summary of the existing results, this paper proposes future development directions including real-time prediction and closed-loop optimization, multi-source data fusion, physical consistency modeling and interpretability enhancement, model migration, and online updating capability. The research aims to provide theoretical support and technical reference for the intelligent development of old oilfields, the construction of digital twin reservoirs, and the prediction of seepage behavior in complex reservoirs. Full article

With economic growth, constructing photovoltaic power plants on gangue mountains holds significant potential for the development of renewable energy and the effective utilization of gangue mountains. However, it is crucial to account for the impact of the spontaneous combustion of coal gangue on surface structures and the mechanical performance of pile foundations. This study uses COMSOL Multiphysics software (version 6.2) to conduct a simulation by establishing a multiphysical coupling model of the temperature field, oxygen concentration field, and seepage velocity field, simulating the dynamic evolution of spontaneous combustion in gangue mountains. The reasonableness of the model was verified by comparison, and a mechanics module was added to explore the effects of pile foundations and ground surfaces at high temperatures. The results indicate that the spontaneous combustion of coal gangue initially generates high-temperature regions beneath the slope of the pile, which gradually expand outward. Due to thermal expansion, thermal stress and displacement occur in both the gangue mountain and pile foundations, potentially compromising the stability of the foundations and increasing the risk of structural failure. These findings can serve as valuable references for the construction of photovoltaic power plants and the effective utilization of gangue mountains. Full article

The phenomenon of tunnel erosion is quite common in the Loess Plateau. Tunnel erosion can cause disasters such as landslides, mudslides, and ground collapses, resulting in significant economic losses and posing a threat to people’s safety. Therefore, understanding the evolution mechanism of tunnel erosion not only helps to analyze and predict the development law of erosion but also has a certain guiding role in engineering activities. Many scholars (including our team) have conducted field investigations and statistical analysis on the phenomenon of tunnel erosion in loess; however, these studies still have shortcomings in visual quantitative analysis. The combination of the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) has significant advantages in studying soil seepage and erosion. Based on existing experimental research, this article combines the Discrete Element Method (DEM) with Computational Fluid Dynamics (CFD) to establish a CFD-DEM coupled model that can simulate tunnel erosion processes. In this model, by changing the working conditions (vertical cracks, horizontal cracks, and circular holes) and erosion water pressure conditions (200 Pa, 400 Pa, 600 Pa), the development process of tunnel erosion and changes in erosion rate are explored. The results indicate that during the process of fluid erosion, the original vertical crack, horizontal crack, and circular hole-shaped tunnels all become a circular cave. The increase in erosion water pressure accelerates the erosion rate of the model, and the attenuation rate of the particle contact force chain also increases, resulting in a decrease in the total erosion time. During the erosion process, the curve of the calculated erosion rate shows a pattern of slow growth at first, then rapid growth, before finally stabilizing. The variation law of the erosion rate curve combined with the process of tunnel erosion can roughly divide the process of tunnel erosion into three stages: the slow erosion stage, the rapid erosion stage, and the uniform erosion stage. Full article

In China, most medium- and shallow-depth coalbed methane (CBM) reservoirs are in the middle to late stages of development. Exploiting CBM in unsaturated low-permeability reservoirs remains particularly challenging. This study investigates the evolution of reservoir pressure in rock strata during CBM extraction from a low-permeability coal seam in the Ordos Basin. By integrating the seepage equation, material balance equation, and fluid pressure theory, we establish a theoretical and numerical model of reservoir pressure dynamics under varying bottom-hole flowing pressures. The three-dimensional surface of reservoir pressure is characterized by the formation of a stable pressure drop funnel. The results show that gas–liquid flow capacity is significantly constrained in low-permeability reservoirs. A slower drainage control rate facilitates the formation of stable seepage channels and promotes the expansion of the seepage radius. Under ultra-low permeability (0.5 mD) to low permeability (2.5 mD) conditions, controlling the bottom-hole flowing pressure below the average value aids the effective expansion of the pressure drop funnel. Numerical simulations indicate that the seepage and desorption radii expand more effectively under low decline rates in low-permeability zones. Calculations based on production data reveal that, under ultra-low permeability conditions, Well V₁ exhibits a narrower and more elongated pressure drop funnel than Well V₂, which operates in a low permeability zone. Furthermore, well interference has a lesser effect on the expansion of the pressure drop funnel under ultra-low permeability conditions. These differences in the steady-state morphology of the pressure drop funnel ultimately lead to variations in production capacity. These findings provide a theoretical foundation and practical guidance for the rational development of low-permeability CBM reservoirs. Full article

In the process of reservoir water flooding development, the characteristics of underground seepage field have changed, resulting in increasingly complex oil–water distribution. The original understanding of reservoir physical property parameters based on the initial stage of development is insufficient to guide reservoir development efforts in the extra-high water cut stage. To deeply investigate the spatio-temporal evolution of heterogeneity in the internal seepage field of layered reservoirs during water flooding development, water–oil displacement experimental simulations were conducted based on layered, normally graded models. By combining CT scanning technology and two-phase seepage theory, the variation patterns of heterogeneity in the seepage field of medium-to-high permeability, normally graded reservoirs were analyzed. The results indicate that the effectiveness of water flooding development is doubly constrained by differences in oil–water seepage capacities and the heterogeneity of the seepage field. During the development process, both the reservoir’s flow capacity and the heterogeneity of the seepage field are in a state of continuous change. Influenced by the extra resistance brought about by multiphase flow, the reservoir’s flow capacity drops to 41.6% of the absolute permeability in the extra-high water cut stage. Based on differences in the variation amplitudes of oil–water-phase permeabilities, changes in the heterogeneity of the internal seepage field of the reservoir can be broadly divided into periods of drastic change and relative stability. During the drastic change stage, the fluctuation amplitude of the water-phase permeability variation coefficient is 114.5 times that of the relative stable phase, while the fluctuation amplitude of the oil-phase permeability variation coefficient is 5.2 times that of the stable stage. This study reveals the dynamic changes in reservoir seepage characteristics during the water injection process, providing guidance for water injection development in layered reservoirs. Full article

Inter-well frac-hit has become an important challenge in the development of unconventional oil and gas resources such as fractured tight sandstone. Due to the presence of hydraulic fracturing fractures, secondary induced fractures, natural fractures, and other seepage media in real formations, the acquisition of stress fields requires the coupling effect of seepage and stress. In this process, there is also stress sensitivity, which leads to unclear dynamic evolution laws of stress fields and increases the difficulty of the staged multi-cluster fracturing of horizontal wells. The use of a multi-stage stress-sensitive horizontal well production stress field prediction model is an effective means of analyzing the influence of natural fracture parameters, main fracture parameters, and multi-stage stress sensitivity coefficients on the stress field. This article considers multi-stage stress sensitivity and, based on fractured sandstone reservoir parameters, establishes a numerical model for the dynamic evolution of the production stress field in horizontal wells with matrix self-supporting fracture-supported fracture–seepage–stress coupling. The influence of various factors on the production stress field is analyzed. The results show that under constant pressure production, for low-permeability reservoirs, multi-stage stress sensitivity has a relatively low impact on reservoir stress, and the amplitude of principal stress change in the entire fracture length direction is only within the range of 0.27%, with no significant change in stress distribution; The parameters of the main fracture have a significant impact on the stress field, with a variation amplitude of within 2.85%. The ability of stress to diffuse from the fracture tip to the surrounding areas is stronger, and the stress concentration area spreads from an elliptical distribution to a semi-circular distribution. The random natural fracture parameters have a significant impact on pore pressure. As the density and angle of the fractures increase, the pore pressure changes within the range of 3.32%, and the diffusion area of pore pressure significantly increases, making it easy to communicate with the reservoir on both sides of the fractures. Full article

By using the principles of porous media seepage mechanics and solute transport theories, a seepage–erosion theory model was developed to uncover the dynamics of mud and water inrush in fault rupture zones during the construction of tunnels. This model consists of a mass conservation equation, a flow transformation equation, a porosity evolution equation, and a permeability evolution equation. These components illustrate the interaction between seepage–erosion particle loss and the transformation of seepage flow patterns throughout the mud and water inrush evolution in the fault fracture zone. This model proves to be effective in illustrating the catastrophic process of mud and water inrushes within tunnels located in fault rupture zones. To address the spatial and temporal variations, the implicit difference and Galerkin finite element schemes were utilized, and the Newton–Raphson iteration method was applied to handle the nonlinear attributes of the equations. The theoretical model underwent further development and numerical simulations were performed using COMSOL multi-field coupling software. A comparison with existing indoor water inrush mud model test results validated the effectiveness of our model. The theoretical model was then applied to the Yong Lian tunnel scenario within the fault rupture zone. This computational analysis exposed the sequence of flow pattern transformations and the instability in seepage–erosion evolution within the fault rupture zone, ultimately leading to the emergence of mud and water inrush disasters. The findings of this study offer valuable insights for addressing tunnel engineering challenges related to underwater inrush disasters. Full article

Previous studies indicate that mass transport deposits are related to the dynamic accumulation of natural gas hydrates and gas leakage. This research aims to elucidate the causal mechanism of seabed seepage in the western region of the southeastern Qiongdongnan Basin through the application of seismic interpretation and attribute fusion techniques. The mass transport deposits, bottom simulating reflector, submarine mounds, and other phenomena were identified through seismic interpretation techniques. Faults and fractures were identified by utilizing variance attribute analysis. Gas chimneys were identified using instantaneous frequency attribute analysis. Free gas and paleo-seepage points were identified using sweetness attributes, enabling the analysis of fluid seepage pathways and the establishment of a seepage evolution model. Research has shown that in areas where the mass transport deposits develop thicker layers, there is a greater uplift of the bottom boundary of the gas hydrate stability zone, which can significantly alter the seafloor topography. Conversely, the opposite is true. The research indicates that the upward migration of the gas hydrate stability zone, induced by the mass transport deposits in the study area, can result in the rapid decomposition of gas hydrates. The gas generated from the decomposition of gas hydrates is identified as the principal factor responsible for inducing seabed seepage. Moderate- and low-speed natural gas seepage can create spiny seamounts and domed seamounts, respectively. Full article

Preferential flow is widely developed in varieties of voids (such as macropores and fissures) in loess areas, affecting slope hydrology and stability and even leading to geological disasters. However, the model of seepage evolution with dynamic preferential flow is not clear, which obstructs the disclosure of the mechanism of landslides induced by the preferential flow. This study aimed to capture the seepage and occurrence status of water in loess voids, explain the variability characteristics of the loess pore structure, and reveal the seepage evolution model of dynamic preferential flow. Preferential infiltration experiments were conducted by combining X-ray computed tomography (X-ray CT) nondestructive detection with contrast techniques under dynamic seepage conditions. Three-dimensional (3D) visualized reconstruction, digital image correlation (DIC), image processing, and quantitative analyses were performed in AVIZO 2019.1, including two-dimensional (2D) and 3D characteristics of preferential flow distribution and macropore changing, dynamic variation of the porosity, pore number, volume, dip angle, and connectivity. Results showed that (1) preferential flow exists under saturated and unsaturated conditions in loess with strong uniformity and anisotropy; (2) preferential flow not only migrates into existing connected macropores, but also connects the original isolated pores into channels and forms larger percolation groups of contrast medium under the gradually increased high pressure; (3) the seepage develops with the evolution model of ‘preferential flow–piston flow–preferential piston mixture flow–piston flow’ in the dynamic process. The new insights into the characteristics of the seepage evolution in undisturbed loess under dynamic preferential flow will enrich the understanding of loess seepage and provided an important reference for future research on the slope instability of the loess induced by preferential flow. Full article

To study the evolution of geological hazard sources of waste dump slopes under rainfall conditions, a physical model of a rainfall-affected slope was designed. The apparent resistivity of the slope rock and soil mass at different rainfall times was measured via the high-density resistivity method, and the formation process of internal disaster sources of the rainfall-affected slope was obtained. The variation characteristics of the resistivity of the rain-affected slope were analyzed when it had a weak surface and crack development. Based on the three-water model and Maxwell conductivity formula, the evolution process of geological hazard sources of the rainfall-affected slope was summarized. A resistivity response mechanism equation for rainfall-induced slope hazard sources was derived and compared to the Archie formula, verifying the model rationality. The test results showed that the behavior of the rainfall-affected slope conforms to the saturated–unsaturated dynamic cycle process. The apparent resistivity was positively correlated with the development of slope pores and cracks and negatively correlated with the water content in the slope. The apparent resistivity increased during fracture development and decreased during water seepage. In the slope failure and disaster process, the apparent resistivity varies under the coupling effect of crack development and water seepage. During the formation of geological hazard sources, the apparent resistivity abruptly changes and fluctuates. Therefore, according to the abrupt changes and abnormal fluctuations in the apparent resistivity detected, the development of geological hazard sources of slopes can be determined. Full article

Long-term development of fluvial reservoirs causes regular changes in the microscopic pore-throat structure, physical properties and phase permeability curves of the reservoirs, and the evolution history of different oil layer varies. These effects can be explored using a four-dimensional (4D) model of the maturing field. The logging curves of 89 sand bodies of the Nanpu No. 2 structure in the Bohai Bay Basin were restored to the non-water flooded state based on the changing status of water flooding layers at different stages and levels, and an original geological model was established by combining data for the old wells. The time-varying relationship was incorporated in the dynamic model with surface flux as the variable, and the numerical simulation analysis was conducted based on the reservoir time-varying characteristics. The results showed that ① the logging data of the water-flooded layer significantly affected the simulation results of the geological model and can only be used for the establishment of the initial geological model after repositioning of time and space; ② the time variation of reservoir properties and relative permeability markedly affected the simulation results of the remaining oil. Reservoir parameters and fluid properties simulated by the 4D model were consistent with the data of water flooded layers in new wells during different periods; ③ the novel method significantly improved the fitting rate of the dynamic model, and the model was used to quantitatively describe the morphology of dominant seepage channels and reservoir variation parameters. The novel idea of ‘retreat as progress’ and ‘bring in to solve’ achieved the solution of the dynamic and static parameters of the 4D model according to each time step of space-time evolution. The results provide a guide for comprehensive adjustment and evaluation of Nanpu Oilfield for 52 well-times with an oil increase of 1.68 × 10⁴ tons for the different stages. Full article