Search Results (115)

Wellbore strengthening is a widely applied technique to mitigate wellbore leakage during drilling operations in complex formations characterized by narrow mud weight windows. This method enhances the wellbore’s pressure-bearing capacity by using lost circulation materials (LCMs) to bridge natural or induced fractures. In recent years, advanced sealing technologies such as wellbore reinforcement have gradually been applied and developed, but their related influencing factors and mechanisms have not been deeply revealed. This article uses the Cohesive module of ABAQUS to establish a wellbore fracture sealing model. By establishing a porous elastic finite element model, the elastic mechanics theory of porous media is combined with finite element theory. Under the influence of factors such as anisotropy of geostress, reservoir elastic modulus, Poisson’s ratio, and fracturing fluid viscosity, the circumferential stress distribution of the wellbore after fracture sealing is simulated. The simulation results show that stress anisotropy has a significant impact on Mises stress. The greater the stress anisotropy, the more likely the wellbore sealing is to cause wellbore rupture or instability. Therefore, it is necessary to choose a suitable wellbore direction to avoid high stress concentration areas. The elastic modulus of the reservoir is an important parameter that affects wellbore stability and fracturing response, especially in high modulus reservoirs where the effect is more pronounced. Poisson’s ratio has a relatively minor impact. In fracturing and plugging design, the viscosity of fracturing fluid should be reasonably selected to balance the relationship between plugging efficiency and wellbore mechanical stability. In the actual drilling process, priority should be given to choosing the wellbore direction that avoids high stress concentration areas to reduce the risk of wellbore rupture or instability induced by plugging, specify targeted wellbore reinforcement strategies for high elastic modulus reservoirs; using models to predict fracture response characteristics can guide the use of sealing materials, achieve efficient bridging and stable sealing, and enhance the maximum pressure bearing capacity of the wellbore. By simulating the changes in circumferential stress distribution of the wellbore after fracture sealing, the mechanism of wellbore reinforcement was explored to provide guidance for mechanism analysis and on-site application. Full article

The nonlocal macro–meso-scale damage (NMMD) model, implemented in the framework of the finite element method, has been demonstrated to be a promising numerical approach in simulating crack initiation and propagation with reliable efficacy and high accuracy. In this study, the NMMD model was further enhanced by employing an identical degradation mechanism for both the tensile and shear components of shear stiffness, thereby overcoming the limitation of equal degradation in shear and tensile stiffness inherent in the original model. Additionally, a more refined and physically sound seepage evolution function was introduced to characterize the variation in permeability in porous media with geometric damage, leading to the development of an improved NMMD model suitable for simulating coupled seepage–stress problems. The reliability of the enhanced NMMD model was verified by the semi-analytical solutions of the classical KGD problem. Finally, based on the modified NMMD model, the effects of preset fracture spacing and natural voids on hydraulic fracture propagation were investigated. Full article

Efficient and accurate modeling of rock deformation and well production in weakly consolidated reservoirs requires reliable and accurate reservoir modeling techniques. During hydrocarbon production, the reservoir pressure is dropped, and rock compaction is induced. In such depletion-induced reservoir rock deformation, both elastic and plastic deformation can be generated. The numerical investigation of depletion-induced plasticity in shale oil reservoirs and its impact on coupled reservoir modeling helps provide insights into the optimization of horizontal well productivity. This study introduces a coupled flow and geomechanical model that considers porous media flow, elastoplastic deformation, horizontal well production, and the coupling between the flow and geomechanical processes. Simulation results are then provided along with numerical modeling parameters. Effects of relevant parameters, including depletion magnitude, rock mechanical properties, and hydraulic fracture parameters, jointly affect rock deformation, rock skeleton damage, and horizontal well productivity. Depletion-induced plasticity, stress, pressure, and subsidence are all characterized by the solution strategy. In addition, the implementation of direct and iterative solvers and the usage of full coupling and sequential coupling strategies are investigated, and the associated solver performance is quantified. It helps evaluate the numerical efficiency in the highly nonlinear numerical system. This study provides an efficient coupled flow and elastoplastic model for the simulation of depletion in weakly consolidated reservoirs. Full article

With the accelerating global transition to clean energy, underground hydrogen storage (UHS) has gained significant attention as a flexible and renewable energy storage technology. Ontario, Canada, as a pioneer in energy transition, offers substantial underground storage potential, with its geological conditions of salt, limestone, and sandstone providing diverse options for hydrogen storage. However, the hydrogen transport characteristics of different rock media significantly affect the feasibility and safety of energy storage projects, warranting in-depth research. This study simulates the hydrogen flow and transport characteristics in typical energy storage digital rock core models (salt rock, limestone, and sandstone) from Ontario using the improved quartet structure generation set (I-QSGS) and the lattice Boltzmann method (LBM). The study systematically investigates the distribution of flow velocity fields, directional characteristics, and permeability differences, covering the impact of hydraulic changes on storage capacity and the mesoscopic flow behavior of hydrogen in porous media. The results show that salt rock, due to its dense structure, has the lowest permeability and airtightness, with extremely low hydrogen transport velocity that is minimally affected by pressure differences. The microfracture structure of limestone provides uneven transport pathways, exhibiting moderate permeability and fracture-dominated transport characteristics. Sandstone, with its higher porosity and good connectivity, has a significantly higher transport rate compared to the other two media, showing local high-velocity preferential flow paths. Directional analysis reveals that salt rock and sandstone exhibit significant anisotropy, while limestone’s transport characteristics are more uniform. Based on these findings, salt rock, with its superior sealing ability, demonstrates the best hydrogen storage performance, while limestone and sandstone also exhibit potential for storage under specific conditions, though further optimization and validation are required. This study provides a theoretical basis for site selection and operational parameter optimization for underground hydrogen storage in Ontario and offers valuable insights for energy storage projects in similar geological settings globally. Full article

To study the effects of liquid properties and interface parameters on gas–liquid two-phase flow in porous media. The volume flow model of gas–liquid two-phase flow in porous media was established, and the interface of the two-phase flow was reconstructed by tracing the phase fraction. The microscopic imbibition flow model was established, and the accuracy of the model was verified by comparing the simulation results with the classical capillary imbibition model. The flow characteristics in the fracturing process and backflow process were analyzed. The influence of flow parameters and interface parameters on gas flow was studied using the single-factor variable method. The results show that more than 90% of the flowing channels are invaded by fracturing fluid, and only about 50% of the fluid is displaced in the flowback process. Changes in flow velocity and wetting angle significantly affect Newtonian flow behavior, while variations in surface tension have a pronounced effect on non-Newtonian fluid flow. The relative position of gas breakthrough in porous media is an inherent property of porous media, which does not change with fluid properties and flow parameters. Full article

The characteristics of CO₂ seepage in reservoirs have important research significance in the field of CCS technology application. However, the characteristics of macro-scale seepage are affected by the geometrical characteristics of micro-scale media, such as pore size and particle shape. Therefore, in this work, a series of numerical simulations were carried out using the phase field method to study the effect of pore structure simplification on micro-scale displacement process. The influences of capillary number, wettability, viscosity ratio, interfacial tension, and fracture development are discussed. The results show that the overall displacement patterns of the real pore model and the simplified particle model are almost similar, but the oil trapping mechanisms were totally different. There are differences in flow pattern, number of dominant flow channels, sensitivity to influencing factors and final recovery efficiency. The real pore model shows higher displacement efficiency. The decrease in oil wet strength of rock will change the CO₂ displacement mode from pointing to piston displacement. At the same time, the frequency of breakage will be reduced, thus improving the continuity of CO₂. When both pores and fractures are developed in the porous media, CO₂ preferentially diffuses along the fractures and has an obvious front and finger phenomenon. When CO₂ diffuses, it converges from the pore medium to the fracture and diverges from the fracture to the pore medium. The shape of fracture development in the dual medium will largely determine the CO₂ diffusion pattern. Full article

Hydrocarbon production in the reservoir depends on fluid flow through its porous media, such as fractures and their physical parameters, which affect the analysis of the reservoir’s physical properties. The fracture’s physical parameters can be measured conventionally by laboratory analysis or using numerical approaches such as simulations with the Lattice Boltzmann method. However, these methods are time-consuming and resource-intensive; therefore, this research explores the application of machine learning as an alternative method to predict the physical parameters of fractures such as permeability, surface roughness, and mean aperture. Synthetic three-dimensional digital fracture data that resemble real rock fractures were used to train the machine learning models. These included two convolutional neural networks (CNNs) designed and implemented in this research—which are referred to as CNN-1 and CNN-2—as well as three pre-trained models—including DenseNet201, VGG16, and Xception. The models were then evaluated using the ${\mathrm{R}}^2$ and mean absolute percentage error (MAPE). CNN-2 was the best model for accurately predicting the three fracture physical parameters but experienced a drop in performance when tested on real rock fractures. Full article

In recent years, fracturing-flooding technology has achieved a series of successful practices in the development of low-permeability oil reservoirs. However, research on the dynamic behavior of fracturing-flooding remains limited. In this paper, a dual medium model considering anisotropic characteristics is established for the target blocks. Multiple sets of conventional water injection transitions and multi-cycle fracturing-flooding operations are designed for simulation to explore the subsequent optimal operational schemes. Simulations are conducted on the optimal transitions between conventional water injection and multi-cycle fracturing-flooding schemes for different reservoir models with varying physical properties to study the dynamic behavior of fracturing-flooding in oil reservoirs with different properties. The results indicate that, for conventional water injection schemes, the optimal transition time for both the target well group and other reservoirs with different properties corresponds to a formation pressure coefficient between 1.2 and 1.3, with the optimal injection–production ratio being 1:1. From the perspective of water cut, the accumulated oil production of multi-cycle fracturing-flooding is higher than that of conventional water injection. The optimal multi-cycle fracturing-flooding schemes for both the target well group and other reservoirs with different properties are to start fracturing-flooding when the formation pressure coefficient is around 0.8 and to begin production when it reaches 1.4. Full article

Background: Pathological bone fracturing is an escalating problem driven by increasing aging and obesity. Bioceramics, particularly tricalcium-phosphate-based materials (TCP), are renowned for their exceptional biocompatibility, osteoconductivity, and ability to promote biomineralization. In the present study, we designed and characterized TCP porous granules doped with strontium (Sr) and copper (Cu) (CuSr TCP). Sr²⁺ ions were selected as Sr plays a crucial role in early bone formation, osteogenesis, and angiogenesis; Cu²⁺ ions possess antibacterial properties. Materials: The synthesized CuSr TCP granules were characterized by X-ray diffraction. Cytotoxicity and cell proliferation analyses’ assays were performed through the lactate dehydrogenase (LDH) activity and CCK-8 viability tests in rat bone marrow-derived mesenchymal stem cells (BM-MSCs). Hemolytic activity was carried out with human red blood cells (RBCs). Early and late osteogenesis were assessed with alkaline phosphatase (ALP) and Alizarin Red S activity in human osteoblast progenitor cells and rat BM-MSCs. The influence of CuSr TCP on angiogenesis was investigated in human umbilical vein endothelial cells (HUVECs). Results: We have demonstrated that media enriched with CuSr TCP in concentrations ranging from 0.1 mg/mL to 1 mg/mL were not cytotoxic and did not significantly affect cell proliferation rate motility. Moreover, a concentration of 0.5 mg/mL showed a 2.5-fold increase in the migration potential of BM-MSCs. We also found that CuSr TCP-enriched media slightly increased early osteogenesis. We also found that Sr and Cu substitutions in TCP particles significantly enhanced the measured angiogenic parameters compared to control and unsubstituted TCP granules. Conclusion: Our results demonstrate that TCP porous granules doped with Sr and Cu are biocompatible, promote osteodifferentiation and angiogenesis, and could be recommended for further in vivo studies. Full article

Polymer gels are one of the most common plugging agents used for controlling CO₂ channeling and improving sweep efficiency and oil recovery in tight fractured reservoirs. However, the in situ gelation behavior and enhanced oil recovery ability of polymer gel in fractured porous media is still unclear. Thus, in this study, the bulk and in situ gelation behavior of crosslinked phenolic resin gel in a long stainless microtube as the fractured porous media was investigated. The enhanced oil recovery ability of phenolic resin gel used for CO₂ channeling was investigated by means of a fractured core model. Results show that, with the increase of polymer and crosslinker concentrations, the bulk gelation time shortens and gel strength improves during the static gelation process. With the increase of polymer concentration and temperature, the in situ static gelation time and dynamic gelation time of the gel system in the microtube are shortened, and the breakthrough pressure gradient increases after gelation. Compared with the in situ static gelation behavior, the in situ dynamic gelation time is prolonged and the breakthrough pressure gradient decreases after gelation. The in situ static gelation time in the microtube is 1.2 times that of bulk gelation time in an ampoule bottle, and the in situ dynamic gelation time is nearly 3 times that of ampoule bottles. When the injected slug volume was 1.0 FV (fracture volume), as the polymer concentration increased from 3000 mg·L⁻¹ to 4000 mg·L⁻¹, the incremental oil recovery increased from 3.53% to 4.73%. Full article

This paper presents a study of the application of the finite element method for solving a fractional differential filtration problem in heterogeneous fractured porous media with variable orders of fractional derivatives. A numerical method for the initial-boundary value problem was constructed, and a theoretical study of the stability and convergence of the method was carried out using the method of a priori estimates. The results were confirmed through a comparative analysis of the empirical and theoretical orders of convergence based on computational experiments. Furthermore, we analyzed the effect of variable-order functions of fractional derivatives on the process of fluid flow in a heterogeneous medium, presenting new practical results in the field of modeling the fluid flow in complex media. This work is an important contribution to the numerical modeling of filtration in porous media with variable orders of fractional derivatives and may be useful for specialists in the field of hydrogeology, the oil and gas industry, and other related fields. Full article

Multi-layer horizontal well development and hydraulic fracturing are key techniques for enhancing production from shale oil reservoirs. During well development, the fracturing performance and well-pad production are affected by depletion-induced stress changes. Previous studies generally focused on the stress and fracturing interference within the horizontal layers, and the infilled multi-layer development was not thoroughly investigated. This study introduces a modeling workflow based on finite element and displacement discontinuity methods that accounts for dynamic porous media flow, geomechanics, and hydraulic fracturing modeling. It quantitatively characterizes the in situ stress alteration in various layers caused by the historical production of parent wells and quantifies the hydraulic fracturing interference in infill wells. In situ stress changes and reorientation and the non-planar propagation of hydraulic fractures were simulated. Thus, the workflow characterizes infill-well fracturing interferences in shale oil reservoirs developed by multi-layer horizontal wells. Non-planar fracturing in infill wells is affected by the parent-well history production, infilling layers, and cluster number. They also affect principal stress reorientations and reversal of the fracturing paths. Interwell interference can be decreased by optimizing the infilling layer, infill-well fracturing timing, and cluster numbers. This study extends the numerical investigation of interwell fracturing interference to multi-layer development. Full article

Numerical simulations play a key role in the optimization of fracturing operation designs for unconventional reservoirs. Because of the presence of numerous natural discontinuities and pores, the rock masses of reservoirs can be regarded as fractured porous media. In this paper, a fully coupled discontinuous deformation analysis model is newly developed to simulate the hydromechanical processes in fractured and porous media. The coupling of fracture seepage, pore seepage, and fracture network propagation is realized under the framework of DDA. The developed model is verified with several examples. Then, the developed DDA model is applied to simulate the hydraulic fracturing processes in fractured porous rock masses, and the effects of rock mass permeability on fracturing are investigated. Our findings suggest that high rock permeability may inhibit the stimulation of fracture networks, while increasing the viscosity of fracturing fluids can enhance the fracturing efficiency. This study provides a valuable numerical tool for simulating hydromechanical processes in fractured and porous media and can be used to analyze various geo-mechanical problems related to fluid interactions. Full article

An in-depth understanding of gas (oxygen and methane) seepage characteristics in coal mine goafs is essential for the safe production of mines and for advancing sustainable development practices within the mining industry. However, the gas distribution and its flow processes still remain ambiguous. In this article, we developed a three-dimensional porous media mining goaf mathematical model (considering the heterogeneity) to analyze the methane and oxygen flow features. Firstly, based on the variation laws of the “three zones”—the free caving zone, fracture zone, and subsidence zone—porosity changes in the vertical direction were set. A three-dimensional physical model of a fully mechanized caving mining area with a “U”-shaped ventilation system was established as the basis, and a COMSOL Multiphysics multi-field coupled model was built. Secondly, based on the established model, the characteristics of porosity distribution, mixed gas pressure changes, and the volume fraction of oxygen in the goaf were analyzed. The results show that as the distance from the working face increases, the compaction intensity in the mined-out area gradually rises, resulting in a decreasing porosity trend. The porosity distribution characteristics significantly impact the mechanical behavior and gas flow. The gas pressure inside the mined-out area is much higher than the surroundings, decreasing with depth. The upper and middle parts have the highest-pressure concentrations, requiring focused assessment and targeted monitoring measures based on the pressure characteristics of different regions. The oxygen concentration gradually decreases with depth due to poor ventilation, leading to potential explosive gas mixtures, necessitating ventilation system optimization, enhanced monitoring, and emergency preparedness. The gas exhibits vertical stratification, with higher concentrations in the upper and deep regions. Targeted drainage and ventilation methods can effectively control the gas concentration and ensure production safety. Full article

A large number of experimental studies have demonstrated that the permeability and damage of rock are not constant but rather functionally dependent on stresses or stress-induced deformation. Neglecting the influence of damage and permeability evolution on rock mechanics and sealing properties can result in an overestimation of the safety and stability of underground engineering, leading to an incomplete assessment of the risks associated with surrounding rock failure. To address this, the damage and permeability evolution functions of rock under compression were derived through a combination of experimental results and theoretical analysis, unifying the relationship between porosity and permeability in both porous media flow and fractured flow. Based on this, a fluid–solid coupled seepage model considering rock damage and permeability evolution was proposed. More importantly, this model was utilized to investigate the behavior of deformation, damage, and permeability, as well as their coupled effects. The model’s validity was verified by comparing its numerical results with experimental data. The analysis results show that the evolution of permeability and porosity resulted from a competitive interaction between effective mean stress and stress-induced damage. When the effective mean stress was dominant, the permeability tended to decrease; otherwise, it followed an increasing trend. The damage evolution was primarily related to stress- and pressure-induced crack growth and irreversible deformation. Additionally, the influence of the seepage pressure on the strength, damage, and permeability of the investigated rock was evaluated. The model results reveal the damage and permeability evolution of the rock under compression, which has a certain guiding significance for the stability and safety analysis of rock in underground engineering. Full article