Fracture Process Research Articles

Coupling of discrete crack and continuous damage model to describe the complete process of concrete fracture

Coupling of discrete crack and continuous damage model to describe the complete process of concrete fracture

Structural Integrity Evaluation Of 3D Printed Graphene-Reinforced Pla Notched Plates Using Failure Assessment Diagrams

Abstract Failure Assessment Diagrams (FADs) constitute a well-known structural integrity evaluation tool that allows structural components containing crack-like defects to be assessed through a simultaneous analysis of fracture and plastic-collapse processes. FADs are included in the most recognized structural integrity assessment procedures/standards, such as BS7910 and API 579/ASME FFS-1, and their use is generally limited to metallic components containing crack-like defects. On the other hand, structural responsibilities are being assumed by 3D printed composites, and particularly by those obtained through FFF (Fused Filament Fabrication), beyond their most extended use as prototyping materials. The resulting structural components may contain notch-type defects (e.g., grooves, corners, holes, etc.) that determine their corresponding structural integrity. Thus, it is necessary to define structural integrity assessment criteria for this kind of materials when containing any kind of stress risers, beyond crack-like defects. This work justifies the use of BS7910 Level 1 FAD, coupled with a notch correction derived from the Theory of Critical Distances (TCD), to analyze graphene-reinforced PLA plates subjected to pure tensile loading conditions and containing U- and V-notches. The results reveal that, for U- and V-notches, the assessment points representing the plates at failure are located within the FAD area corresponding to unsafe conditions, providing conservative evaluations with moderate safety margins. For plates containing circular holes, the proposed approach provides unsafe predictions.

Predicting Fatigue Damage in Hydrogels Through Force‐Induced Luminescence Enhancement

AbstractFatigue damage of polymers occurs under long‐term load cycling, resulting in irreversible fracture failure, which is difficult to predict. The real‐time monitoring of material fatigue damage is of great significance. Here, tough hydrogels are prepared with force‐induced confined luminescence enhancement of carbonated polymer quantum dot (CPD) clusters to realize the visualization of fracture process and the monitoring of fatigue damage. The enhanced interactions induced by force between the clusters and the polymer in the confined space inhibit the non‐radiative leaps and promote the radiative leaps to quantify the fatigue damage into optical signals. Rigid CPDs with abundant active sites on the surface can form dynamic reversible bonds with polymer and dissipate stress concentration, which significantly enhances the crack propagation strain (8000%) and fracture energy (26.4 kJ m−2) of hydrogels. CPD hydrogels have a wide range of applications in novel information encryption and luminescent robotics.

A Novel Hydro‐Grain‐Texture Model to Unveil the Impact of Mineral Grain Anisotropy on Fluid‐Driven Cracking Processes in Crystalline Rock

ABSTRACTThe anisotropy at the grain scale significantly impacts cracking behavior of crystalline rocks. However, the anisotropy of mineral structure, especially the grain shape and orientation has been inadequately addressed in studies on hydraulic fracturing. To bridge this gap, this paper introduces a coupled hydro‐grain‐texture model (HGTM) based on discrete element model (DEM) that investigates the influence of grain shape and orientation on fluid‐driven cracking processes in crystalline rock. The HGTM can consider the different mineral grain shapes and orientations by changing the aspect ratio and rotating coordinate axes. Our studies covered six distinct in‐situ stresses, three grain shapes, and five grain orientations. Initially, we present a comprehensive examination of the microcracking processes of hydraulic fracturing. Then the influences of in‐situ stress, grain shape, and grain orientation on cracking processes were studied. The results underscore that both mineral grain and in‐situ stress interplay to influence the hydraulic fracturing of the crystalline rocks. The proposed HGTM can well mimic the propagation process of hydraulic fracturing by comparing with the experimental results and the results reveal that hydraulic fracturing in crystalline rocks is a highly complex process. This research clarifies the complex interplay between grain texture and hydraulic fracturing, offering invaluable insights for optimizing stimulation practices.

Coal seam penetration enhancement technology integrating hydraulic fracturing fracture development theory

The development process of fractures in coal beds is influenced by many factors, and its development mechanism is complicated and difficult to be predicted accurately. The research addresses the problem of penetration enhancement technology in the process of coal bed methane mining, and designs a method that incorporates the theory of hydraulic fracturing fracture development. In the process, the coal seam structure was studied, the coal rock was cracked using water injection, the fracture development process during hydraulic fracturing was analysed, the numerical simulation model was constructed using the expanded finite element method, and the fluid flow process in the unit was designed. The experimental results show that when the research method is tested for the time-consuming generation of numerical simulation results, the maximum time-consuming generation of is only 92 ms when the fracture length is 10 m, which is shorter than that of other methods; when analysing the results of fracture initiation pressure calculations, the error between the calculation results generated by the research method and the actual measured results in a total of 14 sample points of the two mines is maintained at less than 0.5 MPa; in the analysis of the relationship between the fluid flow rate and the fluid flow rate, the error is kept at less than 0.5 MPa in the case of fluid flow rate exceeding 0.5 ms; the fracture length and the longest fracture radius decreased significantly with the increase of the injection flow rate after the injection flow rate exceeded 0.005 m3/s. It shows that the research method can effectively carry out coal seam penetration enhancement with good computational efficiency and higher accuracy.

Micromechanics and microstructure based machine learning approach: Unveiling the role of porosity and hydrated phases on the tensile behaviour of cement pastes

The fracture process and the mechanical performance of the cement paste rely significantly on its tensile behaviour. Machine learning methods have been recently developed to predict this behaviour based on numerous experimental measurements. Due to multi-phase heterogeneous nature of cement paste microstructure, evaluation of the role of each chemical phase on the cracking of cement paste is necessary to develop optimized binder systems. Numerous experimental tests would be necessary to determine the best cement pastes in a considered environment. Therefore, in this study, a hybrid approach based on an ensemble machine learning model and a microstructure informed micromechanical model is proposed for predicting the tensile behaviour of hydrated cement pastes. The model can be used as a quick prediction tool for tensile strength of a given microstructure or for deep analysis on the optimization of binder system. A Deep Neural Networks (DNN) model was developed by training and validating a large dataset detailing the chemical phase composition, phase volume fractions and the tensile strength of the cement pastes. This dataset covers an extensive range of Portland cements, hydration ages and water-to-cement ratios. It was developed by simulating cement thermodynamics and tensile behaviour using a damage micromechanical model; which is otherwise almost impossible to obtain through experimental means. Additionally, two generative algorithms, tabular generative adversial networks (TGAN) and conditional generative adversial networks (CTGAN), were employed for dataset augmentation as a sampling method for the sensitivity analysis. This machine learning study provides an in-depth investigation to identify the role of volume fraction of solid phases (C-S-H, ettringite, portlandite and hydrogarnet) and micro porosity (dry and filled) in affecting the tensile behaviour of hydrated cement paste. Optimization assessment of the microstructure was then performed using micromechanical analysis and damage propagation in hydrated cement paste phases and porous network.

Influence of Solid Solution Time on Microstructure and Precipitation Strengthening of Novel Maraging Steels

Effective subsequent heat treatment is crucial for achieving the desired microstructure and excellent mechanical properties in laser-deposited high-performance maraging steel. In this paper, we systematically investigate the synergistic relationship and tuning mechanism of different solution treatment times on the microstructure-property synergy of new maraging steels fabricated using laser direct energy deposition (LDED). To determine the optimal heat treatment process, solution treatment was conducted at 840°C for varying durations, followed by aging at 530°C for 2 hours to induce precipitation strengthening. The results indicate that after 2 hours of solution treatment, the alloy exhibits optimal ductility with an elongation of 7.90% ± 0.15%, attributed to the refinement of the martensitic matrix and precipitated phases, along with the formation of a small amount of residual austenite. When the solution treatment time is extended to 4 hours, the alloy achieves its highest tensile strength, reaching 1958 ± 24 MPa. However, the elongation decreases to 7.31% ± 0.12% due to the coarsening of the martensite and secondary phase particles. After 6 hours of solution treatment, significant coarsening and aggregation of the martensite and Fe2Mo intermetallic compounds markedly reduce the hardness, strength, and toughness of the alloy. By adjusting the solution treatment time, the size, morphology, and distribution of the martensitic matrix, Fe2Mo, and nanoscale precipitated phases play a critical role in the strengthening and fracture processes. Therefore, optimizing the precipitation behavior of the martensitic matrix and Fe2Mo intermetallic compounds through rational solution heat treatment is key to enhancing the mechanical properties of laser-deposited new maraging steels.

Numerical investigation on hydraulic fracture propagation mechanism in fault-karst carbonate reservoir

The fault-karst reservoir takes the fault-controlled fracture-cavity system as storage space, which is surrounded by a large number of high permeability zones. The distribution of reservoir seepage field has an important influence on fracture propagation behavior during the hydraulic fracturing process. Based on statistical damage mechanics theory and finite element method, this paper established a seepage-stress coupling numerical model of fracture propagation under the complex medium condition of matrix-cave-natural fracture in fault-karst carbonate reservoir. This new model innovatively considers the effects of matrix seepage, which is generally ignored by the traditional numerical models, for simulating the fluid–solid coupled fracture propagation behavior. The communication mechanism between fracture and cave is first revealed. The influence of geologic and engineering factors, e.g., permeability in high permeability zone around cave and injection rate etc., on hydraulic fracture propagation in fault-karst reservoir is studied. The results show that the high permeability zone around cave can provide sufficient infiltration capacity to communicate fracture with cave in the form of fluid pressure through fluid flow and fluid pressure conduction, even if hydraulic fracture does not directly communicate the cave. Hydraulic fracture is deflected to the direction of cave under the influence of seepage field, but the deflection angle is mostly within 10°. The high permeability of high permeability zone around cave and the short cave offset distance are conducive to the virtual communication between fracture and cave. Communicating fracture with cave in the non-principal stress direction can be accomplished by fluid flow and fluid pressure conduction, optimizing hydraulic fracturing treatment parameters should be performed by choosing lower injection rates and lower fracturing fluid viscosities. This study can provide key technical support and theoretical guidance for oil and gas development in fault-karst reservoir.

Workflow Helps Predict Casing Deformation During Hydraulic Fracturing in Shale Gas

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 4043054, “Casing-Deformation-Risk Prediction With Numerical Simulation During Hydraulic Fracturing in Deep Shale Gas Reservoirs,” by Jianfa Wu, Xuewen Shi, and Qiyong Gou, PetroChina, et al. The paper has not been peer reviewed. _ In this study, a numerical simulation workflow was established based on comprehensive modeling of a time-lapse stress field, hydraulic fracturing simulation, natural fractures, and other weak interfaces to analyze casing-deformation mechanisms of shale gas horizontal wells during the multistage hydraulic fracturing process. The authors write that they aim to guide the prediction of, and provide mitigating solutions for, casing-deformation risks while improving stimulation efficiency. Introduction The burial depth of deep shale gas reservoirs in the southern Sichuan Basin is approximately 3500 to 4500 m. These have complex geological conditions with developed faults and fractures and high in-situ horizontal stresses. During multistage hydraulic fracturing operations in horizontal wells, establishing an effective prediction method for casing-deformation risks in these reservoirs is a challenge. An integrated workflow is proposed to evaluate and predict casing-deformation risks, effectively support hydraulic fracturing operations, and reduce and mitigate casing failure in these reservoirs. Modeling Methodology It is essential to consider the effects of multiscale natural fractures when constructing a 3D stress model. Natural-fracture stability can be evaluated and used to identify unstable fractures that may cause casing failures. The fundamental workflow of predicting and preventing the casing failure is as follows: 1. Build a 3D geological model characterizing the spatial distribution and geometry of faults and natural fractures 2. Construct a 3D stress model to characterize the in-situ stress state 3. Perform numerical simulations of hydraulic fracturing and 4D coupled stress simulation to obtain the stress field during and after hydraulic fracturing 4. Quantitatively analyze the shear slip risks of natural fractures by calculating slip tolerance as an indicator to determine risk levels of casing deformation 5. Optimize and adjust engineering parameters for hydraulic fracturing to reduce and mitigate casing deformation Natural-Fracture Distribution and Model Construction. In this study, natural fractures parameters such as density, strike, inclination, length of extension, and height were obtained. The natural fractures were calibrated and verified with cores and wellbore images. Natural-fracture distribution was then validated with the expected tectonic history and present-day stress regime. In Fig. 1, the left-hand plot depicts the ant-tracking results by seismic attribute, the central plot portrays natural fractures validated by microseismic events, and the right-hand plot illustrates the 3D natural-fracture model. Results showed two major fracture strikes, one in the northeast and the other in the northwest, forming a mesh network distribution that will be used in the stress model, fracturing simulation, and slip analysis.

Case Study: Innovative Approach To Increase Well Productivity by Adapting Drilling Targets and Completion Methodology

_ The discourse regarding US land exploration and production has tended to primarily focus on shale development. While this has pushed the industry to adopt many technologies or applications, the general recipe has been to be faster and cheaper with hopefully more predictable BOE/ft production. However, there are limitations with this approach as it tends to boil down to a choice of substitution rather than true engineering to improve return on investment or improved net present value. The relationship of parent and child well production has introduced a variable that does not necessarily respond to faster and cheaper. In fact, operators may agree that a dissolvable frac plug has application to reduce completion costs while completely disagreeing on the methodology to manage field development and the parent-child interaction. Extensive field study and calibration can determine an optimal solution with varying degrees of predictability (SPE 211899). For example, reservoir depletion and fracture communication can be difficult to accurately plan for in advance. These and several additional parameters are specific to a section, field, or bench and the design and planning process begins anew when drilling locations move a sufficient distance away from the asset in question. The best outcome during the drilling and completion of a child well is to limit the negative impact on parent well production while delivering an economically viable addition to existing production. Acceptable ranges of underperformance with the child well vary, but can be summarized as 20 to 30% less than the parent well (SPE 209171). Additionally, contact from an offset child well fracturing operation can detrimentally affect parent well production temporarily or permanently by increasing water production and decreasing hydrocarbon production. Introduction This case study presents the development of a methodology for optimizing and controlling the hydraulic fracturing process’s parameters by increasing cluster efficiency to 100% and overcoming formation leakoff with eight to 10 times rate per cluster when compared with industry standards. The developed framework is validated through field completion and production data taken from wells located on the Northwest Shelf, within the San Andres formation, specifically straddling the state line of New Mexico and Texas with operations primarily in northeast Lea County, New Mexico, and Yoakum County, Texas. For the purposes of this study, parent wells are wells drilled during Segment 1 (2013 to 2016) and/or the first wells drilled in a section. Child wells are defined as any subsequent wellbore placed in a section amongst current producers Segment 2 (2017 to 2020) and Segment 3 (2022 to 2023). The offset true vertical depth (TVD) of the child wells relative to the parent wells is less than 100 ft and no geologic barrier exists, thus the contribution to production is from the same rock matrix regardless of well vintage.

Effect of pre-shock on the expanding fracture behavior of 1045 steel cylindrical shell under internal explosive loading

Explosively driven expansion fractures in metallic shells will be preceded by a compression shock wave, which inevitably changes the mechanical and microstructural state of the shell materials and thus affects their subsequent dynamic deformation and expansion fracture processes. To understand the influence of pre-shock pressure on the dynamic expansion fracture behavior of metallic shells, the incident shock waves with varying peak pressure were generated in a 1045 steel cylindrical shell by sweeping detonation wave loading. The pre-shock and subsequent expansion fracture processes were continuously diagnosed by combining a high-speed framing camera and the arrayed Photon Doppler Velocimetry (PDV) measurements to obtain the fracture strains at different axial positions (corresponding to different pre-shock pressures). The results clearly show that the pre-shock pressure during detonation loading has a significant effect on the expansion fracture properties of the 1045 steel cylinder; the fracture strain remarkably decreases with the increase of pre-shock pressure from ∼19 GPa to ∼20 GPa and then changes gently in the range of ∼20 GPa to ∼22 GPa. Metallurgical analyses reveal increased densities of microstructural defects, including dislocations and deformation twins, when a shock wave passes through, resulting in a reduced capacity for further defect storage in the shocked metals, ultimately leading to a decrease in the fracture strain during the subsequent expansion deformation process.

A rate-dependent crack bridging model for dynamic fracture of CNT-reinforced polymers

Carbon nanotubes (CNTs) improve the fracture toughness of polymer-based matrix composites by bridging the crack growth path. This research presents a finite element (FE) rate-dependent crack bridging model of Mode-I dynamic crack growth in CNT-reinforced polymers accounting for rate of loading and rapid crack growth. Two distinct CNT bridging and matrix cracking damage mechanisms are taken into account in the fracture process zone (FPZ) accounting for the dissipation of fracture energy. A viscoelastic-viscoplastic material model is adapted for the matrix phase to capture the strain rate effects. The crack in the matrix phase is modeled using cohesive zone elements characterized by experimental data. A rate-dependent traction-separation law obtained from CNT pull-out simulation at relevant crack opening speeds is used to simulate the CNT bridging in the FPZ. Considering the given traction-separation law as a constitutive equation, the CNTs are replaced with non-linear spring elements to facilitate the FE simulation of crack bridging with numerous CNTs in the FPZ. The proposed rate-dependent FE model for crack bridging enables the study of the effect of key CNT factors such as length, orientation, waviness, volume fraction, and agglomeration on fracture energy dissipation at various crack speeds. The developed model can simultaneously consider the interactive effects of all CNT parameters which is useful for considering all processing-induced uncertainties in analyzing the effects of CNTs on the dynamic fracture toughness of nanocomposites.

Experimental study on the Mode l fracture toughness of frozen silty clay incorporating Digital image correlation

To investigate the effects of initial moisture content and temperature on the Mode I fracture toughness (KIc) of frozen silty clay, a series of three-point bending tests were conducted. Rectangular specimens with prefabricated cracks were tested, and digital image correlation (DIC) technology was employed to analyze the microscopic characteristics at the crack tip. The results indicate that the Mode I fracture toughness of frozen silty clay increases with decreasing temperature and increasing initial moisture content. Temperature governs the failure mode, with plastic failure predominantly occurring at high temperatures and brittle failure at low temperatures. Based on the load–displacement curves and DIC recordings, the macroscopic fracture process of the specimens can be categorized into three stages: elastic deformation, formation of the failure surface, and specimen failure. Additionally, the crack propagation process can be further divided into three stages: initiation and development of microcracks, transition from microcracks to macroscopic cracks, and rapid development of macroscopic cracks. These findings provide critical insights for slope stability research in cold regions and offer new perspectives for engineering design and construction in similar environments.

Numerical study on micro-fracture mechanism of rock dynamic failure induced by abrupt unloading under high in-situ stresses

Rock burst is a kind of severe engineering disaster resulted from dynamic fracture process of rocks. The macro failure behaviors of rocks are primarily formed after experiencing the initiation, propagation, and coalescence of micro-cracks. In this paper, the grain-based discretized virtual internal bond model is employed to investigate the fracturing process of unloaded rock under high in-situ stresses from the micro-fracture perspective. The simulated micro-fracturing process reveals that the longitudinal stress waves induced by unloading lead to the visible unloading effect. The influences of in-situ stresses, mineral grain sizes, and grain heterogeneity on rock macro and micro fracture are investigated. Micro-crack areas of tensile and shear cracks and micro-crack angles are statistically analyzed to reveal the rock micro-fracture characteristics. The simulated results indicate that the combined effect of the stress state transition and the unloading effect dominates the rock unloading failure. The vertical and horizontal in-situ stresses determine the stress state of surrounding rock after unloading and the unloading effect, respectively. As the vertical stress increases, the stress level after unloading is higher, and the shear failure characteristics become more obvious. As the horizontal stress increases, the unloading effect increases, leading to the intensification of tensile failure. The mineral grain size and grain heterogeneity also have nonnegligible influences on rock unloading failure. The micro-fracture perspective provides further insight into the unloading failure mechanism of deep rock excavation.

Modeling interactions between hydraulic fracture and pre-existing microcracks in crystalline rocks using hydro-grain-texture model

The heterogeneity of the mineral grains and pre-existing microcracks significantly impacts the cracking behavior of crystalline rocks. However, these characteristics have not been adequately addressed in the existing hydraulic fracturing studies. To bridge this gap, this study introduces a fluid-solid coupling method enhanced by a microcrack simulation component, called Hydro-Grain-Texture Model (HGTM), to investigate the influence of mineral structures and pre-existing microcracks on hydraulic fracturing processes in granite. Compared with existing methods, the HGTM incorporates a “grain growth” algorithm that can more accurately represent the characteristics of mineral grains. This study investigates the base case of intact rock, and four additional cases featuring microcracks oriented in various directions, i.e., horizontal, diagonal, vertical and complex microcracks, under both hydrostatic and non-hydrostatic in-situ stress conditions. The HGTM effectively captures a range of microscopic behaviors during the hydraulic fracturing of granite, including the formation of rock fragments, fracture branches, and dry fractures, among others. Furthermore, by comparing numerical results for breakdown pressure with analytical results, the accuracy of the HGTM in predicting breakdown pressure is substantiated. The findings indicate that mineral structures (grain boundaries) and microcracks contribute to a more intricate pattern of hydraulic fractures propagation. The pre-existing microcracks significantly influence the propagation path of primary hydraulic fractures. Under fluid-driven pressures, these pre-existing microcracks experience shear failure distinct from tensile failure observed in the surrounding rock matrix.

Anisotropic Fracture Evolution and Size Effect of the Fracture Process Zone in Laminated Shales Derived from Digital Image Correlation

Anisotropic Fracture Evolution and Size Effect of the Fracture Process Zone in Laminated Shales Derived from Digital Image Correlation

Investigation of Tensile Properties and In Situ Analysis of Fracture Behavior in High-Porosity Open-Cell Nickel Foam

Nickel foam offers excellent conductivity, a high surface area, and lightweight structure, making it ideal for applications, like battery electrodes, catalysts, and filtration systems. Its durability and corrosion resistance further enhance its performance in various industries. However, few studies focus on the tensile anisotropy of nickel foam and its tensile fracture process. In this study, the anisotropic tensile behavior of nickel foam with varying relative densities has been investigated, along with its tensile fracture behavior using in situ techniques. The tensile properties of nickel foams show strong anisotropy due to the flattening process in the production process. The results show that the tensile properties, including the yield strength, tensile strength, and elastic modulus, increase with the increasing relative density, while the elongation percentage has no relationship with the relative density. The experiment data on tensile strength are in agreement with Gibson’s formula and Liu’s formula. In situ tensile tests are conducted to explore the microscopic fracture mechanism of nickel foam. The results show that the struts of nickel foam are tensile fractures or shear fractures near the joints, and the fracture process of struts is clearly recorded and analyzed. This study is significant as it provides critical insights into the anisotropic tensile behavior of nickel foam and fracture mechanism, enabling the optimization of production processes and broadening its potential applications.

Exceptional strength-toughness-hardness integrated B4C ceramics with synergistic reinforcement of nano-BN and in-situ ceramic phases

Boron carbide (B4C) ceramics with enhanced mechanical properties were fabricated by incorporating nano boron nitride (nano-BN), obtained through high-energy ball milling (HEBM) using ZrO2 balls as the medium, and utilizing the spark plasma sintering (SPS) technique. During the densification process of B4C/nano-BN composite powders, an in-situ reaction between the B4C matrix and ZrO2 resulted in the formation of ZrB2 ceramic phases at 1200–1300 °C. Additionally, the rapid sintering densification temperature of composites is reduced to 1500–1700 °C, approximately 80 °C lower than that required for pure B4C ceramics. Notably, while maintaining a high relative density (99.5 %), the Vickers hardness, flexural strength, and fracture toughness of B4C ceramics reinforced with synergistic effects of nano-BN and ZrB2 fabricated at 1750 °C are significantly improved to reach values of 36.8 ± 0.15 GPa, 701 ± 12 MPa, and 5.01 ± 0.13 MPa m1/2 respectively; representing an increase of 3.5 GPa (10.5 %), 225 MPa (47.3 %), and 1.72 MPa m1/2 (52.3 %) compared to pure B4C ceramics alone. The multiple reinforcement mechanisms including pinning effects provided by nano-BN and in-situ formed ZrB2 ceramic phases, B4C/ZrB2 grain boundary pressure and intracrystalline pressure within B4C, interlayer dislocations of nano-BN and turbulent layer of B4C/BN boundaries contribute to energy dissipation during fracture processes, such as crack deflection, bridging, propagation hindrance and branching effect; ultimately resulting in exceptional strength-toughness-hardness integrated B4C-based ceramics.

Field experiments and main understanding of shale oil hydraulic fracturing

To understand the key processes of hydraulic fracturing in shale oil reservoirs, such as artificial fracture initiation and extension, proppant transportation and settlement, and the influencing factors of post-fracture production, many hydraulic fracturing field tests have been conducted in the United States. Examples include the ConocoPhillips tests and the National Hydraulic Fracturing Experiment. The results have promoted the innovation and development of fracturing technology. A good correlation exists between lithological changes and the roughness of artificial fractures. Although numerous artificial cracks are created, the number that can provide oil and gas seepage is relatively small, determined by the effectiveness of these cracks. The settlement of proppants in actual geological formations involves factors such as geology, lithology, fractures, and stress. The pressure data indicate that when the reservoir pressure drops below the bubble point pressure, the decline in production sharply increases. The key variables affecting shale oil well production include the horizontal well position, well spacing, horizontal section length, and sand addition intensity. These technologies are suitable for the adaptive process of China’s terrestrial shale oil fracturing, promoting the development and rapid increase of shale oil production.

Longitudinal weight and plantar pressure distribution while standing after tibial or malleolar fractures in patients with or without fracture union

Fracture healing is usually monitored by clinical impressions and radiographs. Objective and easy methods for assessing fracture healing without radiation would be beneficial. The aim of this study was to analyse whether weight and plantar pressure while standing can be used to monitor healing of tibial or malleolar fractures and whether these parameters can discriminate between patients with and without union. Thirteen patients were longitudinally assessed during each postoperative clinical visit, of whom two developed a nonunion. Eleven matched healthy controls were assessed once. Additionally, five patients already experiencing nonunion were assessed once at the time of their nonunion diagnosis. All participants performed a standing task for ten seconds with pressure-sensing insoles. Greatest improvements were detected throughout the first three months in patients with union. However, six months after surgery, more than half of the parameters were still significantly different from those of the controls. The weight and pressure distributions did not differ between patients with or without union six months after surgery. A standing task can be used to monitor improvements in weight and pressure distribution throughout the healing process of tibial or malleolar fractures, but lacks potential to discriminate between patients with or without fracture union.