Distribution Characteristics Of Fractures Research Articles

Combined effects of the roughness, aperture, and fractal features on the equivalent permeability and nonlinear flow behavior of rock fracture networks

The hydraulic properties of a fractured rock mass are largely controlled by connected fracture networks. A thorough understanding of the physical flow processes in fracture networks is essential for assessing the transport capacity of the rock mass. However, the fracture surface roughness morphology, fracture distribution characteristics, and fluid flow regimes strongly influence the flow capacity of a fracture network. To this end, the rough topographic characteristics of fracture surfaces were quantified using fractal theory, and then the effective permeability model and nonlinear seepage effect assessment model of the rough fracture network for different flow regimes were developed based on the possible occurrence of laminar and turbulent flows in a single fracture. Finally, the influences of the geometric parameters of the fracture network on the effective permeability and nonlinear flow characteristics were analyzed. The results show that the prediction results of the proposed models are in good agreement with the field test data and can effectively reveal the seepage influence mechanisms under different flow regimes. Additionally, the results show that the effective permeability is closely related to the fractal dimension, relative roughness, aperture scale, distribution characteristics, and hydraulic gradient of the fractures. The nonlinear behavior of fluid flow significantly reduces the effective permeability of the rock mass. The proposed models can provide a reference for evaluating the transport capacity of rock masses under different fracture distributions and flow regimes.

Fracture and porosity evolution of coal under uniaxial compression: An in-situ X-ray tomography study

To investigate the meso-structure evolution and fracture mechanism of coal under uniaxial compression, an X-ray three-dimensional scanning microscopy in-situ loading test bench was used to conduct a uniaxial compression test of coal. CT data were obtained under different strain conditions and combined using 3D visualization software. According to the surface porosity under different axial forces shows stages in the Z axis, the 3D reconstruction of coal was divided into three regions to compare its structural evolution law. The results show that the uniaxial compression of coal presents staged fractures, and the distribution characteristics of fractures and pores are closely related to internal stress propagation. With the axial force loading, the internal fractures continued to expand, accompanied by the generation of micro-fractures. The development degree of penetrating fracture and lateral strain in region 1 were always higher than in region 2 and region 3, which is more obvious after the scan D; During the whole process of uniaxial compression, the three regions interacted with each other, and the energy transferred between regions has a “hysteresis”. The failure response of region 1 to axial force was earlier than that in region 2, and region 2 was earlier than region 3. However, the fracture evolution behavior of the same region, the three regions showed consistency; After scan D, the meso-structure changes of region 1 were more significant than the other two regions; The coal was locally deformed and destroyed under the action of axial force, resulting in isolated pores and micro-fractures. The spatial distribution of pores and fractures, the existence of micro-fractures and the interaction among different regions aggravated the uneven distribution of axial force in coal, which has a great influence on the fracture process of coal, so that the failure of coal present stages.

A new rock fracture reconstruction method under the constraints of microseismic location and focal mechanism

Under mining conditions, rock masses can experience progressive damage that leads to fracture initiation, propagation and coalescence and thus trigger fracture-controlled disasters, which are dynamic and complex. Therefore, the dynamic characterization of three-dimensional (3D) fractures is critical for revealing disaster-causing mechanisms of rock masses and preventing disasters and has become one of the important problems in the engineering rock mass. This paper proposes a new 3D rock discrete fractures reconstruction method that incorporates microseismic (MS) event location and focal mechanism constraints. The proposed method incorporates a statistical outlier removal (SOR) algorithm, a Gaussian mixed model with expectation maximization (GMM-EM) algorithm for MS events clustering, an intensity-weighted total least square (IWTLS) algorithm for fracture fitting, and moment tensor inversion (MTI) method for fracture orientation optimization. In addition, laboratory uniaxial compression tests with acoustic emission (AE) monitoring were conducted to verify the applicability of the proposed method. Finally, the proposed method was applied to an iron mine with water inrush disasters. The formation process and distribution characteristics of fractures that control water inrush channels were analyzed, and formation mechanisms of water-conducting fractures induced by the mining were determined. The proposed method helps to characterize the dynamic evolution of fractures during rock mass failure under mining disturbance and provides a new idea for recognizing the failure mechanism of rock masses and calibrating water inrush channels.

Study on Calculation Method of Heat Exchange Capacity and Thermal Properties of Buried Pipes in the Fractured Rock Mass-Taking a Project in Carbonate Rock Area as an Example

Fractures are developed in carbonate rock areas, and the fracture water flow significantly influences the heat exchange between buried pipes and the rock mass by induing heat convection, providing the carbonate rock area a strong heat exchange capacity and preferable conditions for shallow geothermal development and utilization. In this paper, the calculation method of heat exchange capacity of buried pipes based on fracture distribution characteristics is proposed and deduced, featuring such advantages as quick speed and low cost. Taking an actual project in carbonate rock area as an example, the heat exchange capacity of buried pipes was obtained by the following two methods: in-situ thermal response test and calculation based on fracture distribution characteristics. In the thermal response test, the initial ground temperatures of the two test holes were 15.18 °C and 12.72 °C. By fitting the linear equation of time and average temperature with a linear thermal source model, the heat exchange capacities were 57.21 W/m and 58.22 W/m, the thermal conductivities were 3.56 W/(m·K) and 2.32 W/(m·K), the thermal diffusivities were 1.71 × 10−6 m2/s and 1.12 × 10−6 m2/s, and the volume specific heat capacity was 2.08 × 106 J (m3·K). The test results indicated that the thermal property parameters of rock and soil mass were higher than those of other areas, with obvious wide-range distribution characteristics. Through the statistical analysis of outcrop fracture characteristics, combined with the cube law to calculate the fracture water flow and convective heat transfer, an alternative method for the calculation and optimization of buried pipe heat transfer in fractured rock mass area is also proposed in this paper. According to the measured fracture distribution characteristics of the field outcrop, the heat exchange capacities of the two holes were 57.26 W/m and 58.56 W/m, which were basically consistent with the thermal response test values and verified the reliability of the calculation method of heat exchange capacity of buried pipes based on fracture distribution characteristics.

Shallow Failure of Weak Slopes in Bayan Obo West Mine.

The slope stability of large open-pit mines has always been a concern and the analysis of large-scale slope landslides is a focus. However, shallow failure in soft rock slopes also has a serious impact on safe production. The northern slope of Baiyunebo West Mine has many shallow landslides in the final slope, resulting in damage of the maintenance channel of the belt transportation system, which has a serious impact on the safety of production. In order to reduce the shallow failure in weak rock slope, it is necessary to analyze the behavior and characteristics of shallow failure in weak rock. Firstly, the mechanical parameters of the intact rock were obtained by using the exploration data; secondly, through the analysis of blasting-damage range, the distribution characteristics of fractures after the failure of weak rock were obtained. Finally, through theoretical analysis, numerical simulation, surface displacement monitoring and on-site shallow-failure case analysis, the deformation and characteristics of shallow failure of weak rock slope in West Mine were obtained. It was found that the mechanical parameters of rock mass strength on the surface of weak rock slope and the original rock were quite different after mining disturbance. The mode of failure of shallow weak rock slope in the West Mine was creep-cracking; the numerical modelling analysis was carried out by using the assignment method of shallow lithology weakening and gradual change, which is more in line with the deformation characteristics of weak rock slope in West Mine. The lower deformation of the soft rock slope in West Mine is 3–5 times that of the upper deformation. The research results are helpful to understand the influence of blasting on the stability of soft rock slope. At present, West Mine has started to adjust blasting parameters according to the research results, so as to reduce the excessive damage of blasting to rock mass, so the stability of the slope is improved.

Epidemiological characteristics of fractures of spine, hip, proximal humerus and forearm during the haze epidemic period

BackgroundAir pollutants have an impact on the occurrence of spine fractures, hip fractures, proximal humerus fractures and forearm fractures. This study aimed at evaluating the short-term impact of particulate matter with aerodynamic diameters of less than 2.5 µm (PM2.5) on the occurrence of those fractures in Shijiazhuang, Hebei, China. MethodsThe daily meteorological, pollution, and fracture data of Shijiazhuang from 2014 to 2019 were collected. Distribution characteristics of fractures were described using descriptive epidemiological methods. The distributed lag nonlinear model (DLNM) was used to reveal the description of those fractures in the exposed and lag dimensions at the same time. Based on gender and age (<18 years old, 18–69 years old and >69 years old), stratified analysis was performed. Sensitivity analysis was performed to ascertain the robustness of the results. ResultsBetween 2014 and 2019, fracture incidences in Shijiazhuang exhibited an overall increasing trend, with an obvious seasonality. PM2.5 was positively related to daily fracture cases and the effects were more obvious in women, adolescents and people of working age. When PM2.5 concentrations increased by one interquartile range (IQR) (70 μg/m3), RR exhibited a unimodal distribution. Its peak appeared on the 16th day of lag (RR=1.005987, 95% CI:1.002472,1.009652), and the RRs were also statistically significant from the 10th to 22nd day of lag. Similarly, cumulative effects of each increase in the concentration of PM2.5 IQR also showed a unimodal distribution. The largest cumulative effect occurred on the 28th day of lag (RR=1.084457, 95% CI:1.012207,1.161864), and the cumulative RRs were also statistically significant from the 19th day to 30nd days. In the dose-response relationship, as PM2.5 concentrations increased, RR increased. ConclusionYear by year, fractures in Shijiazhuang City exhibited an increasing trend. PM2.5 can affect the occurrence of those fractures. The impact on women, adolescents and people of working age is even greater. The supervision of PM2.5 should be strengthened while large-scale emissions should be limited.

Study on the damage characteristics of overburden of mining roof in deeply buried coal seam

The study of water-conducting fracture zone development height is key to the scientific prevention and control of water damage in mines. Based on the geological conditions of the Wenjiapo coal mine in Binchang, China, this paper investigates the development of water-conducting fracture zone in overlying bedrock during mining under large buried depth and huge thick aquifer by combining on-site well-location microseismic monitoring and laboratory similar material simulation. To overcome the limitation of the " limited outlook " of water-conducting fracture zone investigation, the spatial development characteristics of roof fissures in coal seam mining were determined by on-site " the underground - ground" combined microseismic monitoring and follow-up monitoring, and the development of overlying rock fracture under the large depth of burial was concluded. The fractures were mainly distributed in the upper part of the protective coal pillar on both sides of the working face, but less in the upper part of the working face, and primarily distributed in the protective coal pillar on the side of the working face and the adjacent mining area. To verify the accuracy of the conclusion, the overlying bedrock movement and deformation characteristics and the development process of the hydraulic fracture zone during coal seam mining were analyzed by simulating similar materials in the laboratory, using the monitored area as a prototype. The results show that the development height of the mining fracture zone obtained from microseismic monitoring is basically consistent with the simulation results of similar materials. The research finding have significant implications for the study of fracture distribution characteristics and the evolution law of mining overburden, and provide a foundation for scientific prevention and control of water damage on the roof.

Fracture Distribution Characteristics in Goaf and Prevention and Control of Spontaneous Combustion of Remained Coal under the Influence of Gob-Side Entry Retaining Roadway

Based on the ventilation characteristics of the gob-side entry retaining face, a mathematical model of spontaneous combustion in the gob-side entry retaining face is established. From the overburden caving of the goaf along the goaf retaining roadway, the development characteristics of rock strata and residual coal fissures in the goaf are summarized and analyzed. In addition, by using numerical simulation software, the effects of normal mining period, goaf retaining roadway as return air roadway, air leakage prevention, and nitrogen injection measures in goaf on spontaneous combustion in goaf are studied, and the distribution characteristics of flow field, oxygen concentration field and temperature field in goaf are obtained. The results show that the mining of the Geng 20 working face has a significant impact on the Geng 19 coal seam. The Geng 19 coal seam is in the range of fracture zone, and the fracture is well developed. Furthermore, the permeability coefficient of the Geng 19 coal seam increases sharply, air leakage in the goaf is increased along the goaf retaining roadway, and the range of oxygen concentration is enlarged, which results in a temperature rise in the goaf. Therefore, air leakage measures are proposed along the goaf to inject 900 m3/h of nitrogen into the goaf, which can prevent the spontaneous combustion of coal left over in the goaf. In addition, according to the characteristics of fracture development and numerical simulation of spontaneous combustion in goaf under the goaf retaining roadway, the hierarchical prevention, control, and fire extinguishing technology system of the goaf retaining roadway is constructed.

Image-processing-based model for the characterization of surface roughness and subsurface damage of silicon wafer in diamond wire sawing

The damages of silicon wafer in diamond wire sawing have a significant impact on its mechanics, economy, and use properties, which should be evaluated accurately and quickly. A theoretical model is developed to determine the surface roughness Rz (ten-point mean height) and subsurface damage (SSD) depth by the fracture width of silicon wafer. The model takes into account the scratch groove direction and material pile-up effect of silicon wafer. A digital image processing method is integrated into the model to extract the fracture parameters of silicon wafer. Many silicon wafers are processed under different slicing parameters, for which the fracture parameters and surface roughness Rz are measured by confocal microscopy, and the SSD depth is measured with the method of cross-section scanning microscopy. The scratch-induced material pile-up height is evaluated by nanoscratching. The calculated and measured fracture parameters, surface roughness Rz, and SSD depth are analyzed by contrast. The result shows that the model can accurately and quickly determine the surface roughness Rz and SSD depth with an average relative error of less than 12.0% in 20 s. The distribution characteristics of fractures, surface roughness, and SSD are analyzed. The result shows that more fractures have relatively smaller fracture width, depth, length, or related SSD depth. The image-processing-based model would be a reasonable approach for estimating the damages in silicon wafers during wire sawing.

Study on Stability of Stope Surrounding Rock under Repeated Mining in Close-Distance Coal Seams

In order to study the influence of roof stress and fracture distribution characteristics on the stability of stope surrounding rock under repeated mining in close-distance coal seams, the research background of this paper is the close-distance coal seam mining of a mine in Guizhou province, China. The dynamic evolution characteristics of stope roof caving and the stress environment change law under repeated mining are studied by using the method of similar simulation experiment, numerical simulation, and field verification. The results show that the roof stage under repeated mining can be divided into four stages: normal mining, roof deterioration, end face roof leaks, and support crushing. The tip-to-face distance, support height, and support working condition are the main influencing factors in end face roof control. The main reason for the support crushing is that the roof above the support is broken, the main roof cannot form the self-stable structure, and the support force is insufficient. The roof dynamic load is high, and the subsidence of the end face roof is large, which is prone to roof caving during the stope roof weighting. Moreover, the roof weighting is frequent under repeated mining, which leads to the broken roof and the support cannot be supported, resulting in the occurrence of the support crushing accident. The control strategies for stope roof under repeated mining are provided based on the thorough study findings. The working face 17101 roof is successfully controlled by the aforesaid procedures, which provides the foundation for the management of stope surrounding rock under repeated loading.

Numerical Simulation of Gas-Water Two-Phase Flow in Deep Shale Gas Reservoir Development Based on Mixed Fracture Modeling

Abstract In this paper, the development of a three-dimensional, two-phase fluid flow model (Modified Embedded Discrete Fracture Model) to study flow performances of a fractured horizontal well in deep-marine shale gas is presented. Deep-marine shale gas resources account for nearly 80% in China, which is the decisive resource basis for large-scale shale gas production. The dynamic characteristics of deep shale gas reservoirs are quite different and more complex. This paper uses the embedded discrete fracture model to simulate artificial fractures (main fractures and secondary fractures) and the dual-media model to simulate the mixed fractured media of natural fractures and considers the flow characteristics of partitions (artificial fractures, natural fractures, and matrix). Gas desorption is considered in the matrix. Different degrees of stress sensitivity are considered for natural and artificial fractures. Aiming at accurately simulating the whole production history of horizontal well fracturing, especially the dynamic changes of postfracturing flowback, a postfracturing fluid initialization method based on fracturing construction parameters (fracturing fluid volume and pump stop pressure) is established. The flow of gas and water in the early stage after fracturing is simulated, and the regional phase permeability and capillary force curves are introduced to simulate the process of flowback and production of horizontal wells after fracturing. The influence of early fracture closure on the gas-water flow is characterized by stress sensitivity. A deep shale gas reservoir of Sinopec was selected for the case study. The simulation results show it necessary to consider the effects of fractures and stress sensitivity in the matrix when considering the dynamic change of production during the flowback and production stages. The findings of this study can help for better understanding of the fracture distribution characteristics of shale gas, shale gas production principle, and well EUR prediction, which provide a theoretical basis for the effective development of shale gas horizontal well groups.

Macro and micro grouting process and the influence mechanism of cracks in soft coal seam

Grouting is an important method to reinforce soft coal roadway, and the presence of primary cracks in the coal body has an important influence on the grouting effect. With the discrete element simulation method, the grouting process of the soft coal seam was simulated. The mechanism of primary cracks on grouting was revealed, while the influence of fracture characteristics and grouting pressure on the grouting effect was analyzed. The results demonstrated that grouting in the soft coal seam involves the stages of seepage, rapid splitting, slow splitting, and stability. Due to the presence of primary cracks, the grouting diffusion radius increased significantly. Under the slurry pressure, the tensile stress concentration was formed at the crack tip, and the slurry split the coal once the splitting pressure was reached. In addition, the distribution characteristics of fractures are found to have a great influence on the grouting effect. It is observed that smaller fracture spacing is associated with a larger slurry diffusion radius and thus easier penetration of the primary crack tips. The fracture angle affects the direction of fracture propagation. The secondary fracture formed by splitting is a tensile fracture, which is more likely to extend along the direction parallel to the maximum principal stress. Overall, these simulation results have guiding significance for the setting of reasonable spacing of grouting holes in the practice of grouting engineering.

Physical Simulation of Strata Failure and Its Impact on Overlying Unconsolidated Aquifer at Various Mining Depths

Underground mining severely lowers the water table and worsens the ecological environment. To determine the mechanism influencing drawdown in unconsolidated aquifers induced by deep mining combined with overburden movement, with a view to environmental protection, physical simulations for three different depths were designed to investigate and contrast deformation and fracture distribution characteristics at diverse depths after mining. The impacts on overlying unconsolidated aquifers were then analyzed by monitoring overburden movement and ground water level data, and the deformation limit was estimated. Modeling results indicated that coal mining had different impacts on the overlying unconsolidated aquifer via various mechanisms of groundwater level reduction. The aquifer outside the fractured water-conducting zone could be affected by coal mining, and the water tables dropped rapidly. The failure and the deformation features of the aquitard floor were the key to revealing the mechanism of groundwater depletion in deep mining. The effects on aquitard decreased as the distance from the working face increased. A relationship between the strata deformation and the drawdown rate was established; that is, the rate of decline of the groundwater level did not accelerate until the maximum subsidence of the aquitard floor exceeded approximately 0.9 m, or the subsidence-bending area of the aquitard floor exceeded approximately 156 m2.

Distribution Characteristics of Fractures in the Volcanic Reservoirs of Songliao Basin, China

In order to clarify the relationship between fractures and gas accumulation, using data of cores, image logs and experimental analysis, we analyzed the fracture genetic types, development characteristics, controlling factors, distribution rules and formation periods. And then, by combining the evolution of source rock, activity periods of gas source faults and the evolution of cap rock sealing ability in the study area, we discussed the relationship between tectonic fractures and gas accumulation. The results show that there exist primary fracture and secondary fracture in the volcanic rocks of Yingcheng Formation in Songliao Basin. Between the two types, the secondary facture is dominant. Tectonic fractures are controlled by lithology, lithofacies and faults in the plane, and by unconformities vertically, with the characteristics of distribution of cycles. The tectonic fractures formed in three phases, wherein the second period coincides with the hydrocarbon generation peak period. During the second period, gas source faults are active and cap rock had a better sealing ability. This period is the main hydrocarbon accumulation stage in the study area.

Distribution Characteristics of Fractures in the Ultra-Low Permeability Reservoirs of Anpeng Oilfield, China

Using the data of cores, outcrops, thin sections and image logs, we analyzed the fracture distribution characteristics in the ultra-low permeability reservoirs of Anpeng oilfield. Then, we analyzed the main factors controlling the development of fractures. There are tectonic fractures and diagenetic fractures in the ultra-low permeability reservoirs. Tectonic fractures with high dip-angle are the main fracture type. Under the stresses resulting from horizontal tectonic compressions in the Early and Late Himalayan movements, three sets of tectonic fractures formed in the study area, i.e. E-W, NE-SW and NW-SE orientations. The E-W oriented fractures are developed better, then the NE-SW and NW-SE oriented fractures. The formation and distribution of these tectonic fractures are controlled by the tectonic stress field, lithology, porosity, permeability, layer thickness and structures. Under the same controlling factors, the origin types, occurrences and development characteristics of fractures in shallow-to mid-depth reservoirs are similar to that in the deep reservoirs. But fractures developed better in the deep reservoirs than that in the shallow-to mid-depth reservoirs.

Analysis on Earth Stress and Fracture Distribution Characteristics with Image Logging

The generation of Damintun Depression base-rock reservoirs are mainly controlled by fracture development. Currently, for the fracture-system space distribution characters, we haven’t understood clearly. Therefore, we must find fracture developing zones and learn their development state in order to study the planar distribution law of factures. The principal stress was calculated and fractures were identified using sonic and electrical image logging data. Combined with the relationship in borehole breakout method that borehole collapse direction was substantially perpendicular to principal stress direction, the modern horizontal principal stress was determined. Then the base-rock fractures were extracted manually in imaging interactive interpretation graphic. Thus the relation is obtained that the maximum horizontal Earth stress direction is vertical to fracture distribution, and the structural-zone faults are consistent with the fracture distribution law.

On the Forward Simulation of the Geophysical Characteristics in Fractured Reservoirs

Anisotropic information of pre-stack 3D azimuth P wave from seismic data is already one of the most efficient and economic methods from reservoir fracture examination, which requires a wide azimuth for seismic data gathering. By forward simulation of the geophysical characteristics in fractured reservoirs, the relationship between azimuth distribution areas of seismic data gathering and fracture direction is studied. Narrow azimuth for seismic data gathering is also somewhat effective to describe fracture distribution characteristics. In addition, significant seismic property difference (amplitude, damping and frequency) can be made in fractured reservoirs, thus, fracture can be effectively examined by the seismic information of different offsets. All the results in the paper get excellent practical application.

Research on Distribution and Evolution Law of the Damage-Fracture Field in Mining Process

The distribution and spatiotemporal evolution law of the mining-induced fracture field was studied by means of damage mechanics. The damage variable correlated with the excavation process was introduced, which was used to describe the distribution characteristics of fractures in rock mass. In accordance with the damaged theory, the elastic finite element program was developed, by which the analysis of mining process of one coal seam was made of. The material damage accumulation taken into consideration, the distribution and evolution law of the volumetric strain, stress and damage field was obtained, which provided a theoretic reference for the design of gas drainage and improving the efficiency of gas extraction.