Fracture System Research Articles

The importance of the thickness of femoral lateral wall for treating intertrochanteric fractures: a finite elements analysis

To explore how the thickness of the femoral lateral wall influences the effectiveness of internal fixation systems used to treat intertrochanteric fractures. CT images of the pelvis and femur of a male adult were used to construct an intertrochanteric fracture model (AO/OTA 31-A2) with various thicknesses of the femoral lateral wall (FLW). Four finite element (FE) models were created with the lateral femoral walls being 10 mm, 20 mm, 30 mm, and 40 mm thick. The fracture models were fixed with a dynamic hip screw (DHS), a proximal femoral nail anti-rotation (PFNA), and a proximal femoral locking compression plate (P-FLCP). A simulated vertical load was applied to the femoral head. The stress and displacement of the implant and femur in each model were recorded for comparison. The FE analysis of the intertrochanteric fracture models showed that the PFNA system could provide better stability than the DHS and P-FLCP with the same thickness of FLW. The FLW provided buttress support to the femoral head and neck when using a DHS and PFNA, and the buttress strength was proportional to the thickness of FLW. The maximum stress in the DHS model was recorded on the DHS plate which accommodated the lag screw. For the PFNA model, the maximum stress appeared at the connection between the nail and blade. In the P-FLCP model, the maximum stresses were highly concentrated at the connection between the cephalic nails and the proximal plate. The thickness of the femoral lateral wall should be considered an important factor when selecting a suitable internal fixation system for intertrochanteric fractures. Based on the FE analysis, intramedullary fixation, such as PFNA, experiences lower stress levels and a moderate displacement in comparison to DHS and P-FCLP when used to treat intertrochanteric fractures.

Multidisciplinary Integrated Approach Unlocks Fracture-Characterization Ambiguity

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 213771, “Unlocking Fracture-Characterization Ambiguity: A Multidisciplinary Integrated Approach,” by Ali Abughneej, Mohamed Al-Naqeeb, and Mohammed Al-Ostath, SPE, Kuwait Oil Company, et al. The paper has not been peer reviewed. _ Fracture systems play a significant role in production in the case of tight, low-porosity complex reservoirs. An exploration well in North Kuwait that targeted the Middle Marrat formation encountered uncertainty regarding reservoir compartments in an underexplored field, with minimal offset wells to properly evaluate its potential. A multidomain approach is proposed leveraging different types of expertise to tackle the petrophysical and geomechanical aspects of the fracture system governing the carbonate layer and assess its producibility and qualification for stimulation through hydraulic fracturing. Introduction A comprehensive study was performed on Well A targeting the Marrat formation, a tight, low-permeability carbonate Jurassic reservoir. During the last two decades, the operator has drilled many vertical and deviated wells through this formation. Hydrocarbon production from the closely spaced wells shows a major variation in flow rates, which has been attributed to the presence of uncharacterized fracture clusters as well as the limited understanding of reservoir compartmentalization. To address the challenges of production discrepancy, an innovative multidomain approach was proposed as an integrated solution in an attempt to understand the fracture systems governing the reservoir setting and its compartments and further assess their connectivity and extent to form a perspective on their possible contribution or hindrance to flow. An end-to-end comprehensive work flow was created combining the results of advanced formation evaluation, high-resolution borehole imaging, and state-of-the-art sonic imaging [the 3D far-field sonic (3DFFS) approach], followed by a fracture-stability analysis for the purposes of completion optimization and potential future hydraulic fracture design. Geological Setting Middle Marrat is targeted as the hydrocarbon-bearing zone, consisting of dolomitized oolitic grainstone to packstone facies, reflecting the high-energy inner-midramp shoal depositional environment.

Early Failure of Locking Compression Plates in Pediatric Proximal Femoral Fracture

Background: Although proximal femoral locking compression plates (PF-LCP) have been used with increasing frequency in the fixation of proximal femoral fractures in the pediatric population, there is a lack of literature regarding their use. The purpose of this study was to examine the failure rates of PF-LCP fixation in comparison to other accepted fixation methods within a pediatric population.Methods: Retrospective review identified consecutive children treated for proximal femoral fractures from September 2008 to February 2019, who had a minimum follow-up of 12 weeks. Patient charts and radiographs were reviewed, and demographic information was compiled. In the case of failures, timing and method of failure were documented.Results: Sixty-four proximal femoral fractures (61 children) were studied. The average age at the time of presentation was 10.4 years. Twenty-six fractures were treated with PF-LCPs and 38 with other fixation methods (compression hip screws, rigid locked intramedullary nailing, cannulated screws, or a combination of hip screw side plate and intramedullary nailing). Failure occurred in four of the 26 fractures treated with locking compression plating (15.4%) compared to none of the 38 treated with other fixation types (p<0.05).Conclusions: This study demonstrates a higher rate of failure in proximal femoral fractures, particularly basicervical and transcervical femoral neck fractures, treated with locking compression plates (12.9%) compared to 0% other fixation methods (no failures). As a result of this study, we no longer use locked plating systems for pediatric femoral neck fractures at our institution.Level of Evidence: Level III Key Concepts•Proximal femoral fractures account for less than 1% of all fractures in children.•Locking compression plates are being more frequently used in pediatric proximal femoral fractures.•Outcome studies are limited because of the low incidence of these fractures and relative recent introduction of this fixation method.•Proximal femoral compression locking plates had a higher rate of early mechanical failure than other fixation modalities in this study.•The increased risk of failure with proximal femoral compression locking plates should be considered before opting for these implants.

Modelling of flow through naturally fractured geothermal reservoirs, Taupō Volcanic Zone, New Zealand

BackgroundNumerous fractures are observed in fractured geothermal reservoirs on borehole images in the Taupō Volcanic Zone (TVZ), Aotearoa New Zealand. These fractures are necessary to explain the sustained reservoir permeabilities despite the low matrix porosity. However, conventional continuum models do not adequately represent fluid flow through these fractured rocks.MethodsWe present new Discrete Fracture Network (DFN) codes that model fractures and associated fluid flow in 2-D at reservoir scales to represent typical rock types found in TVZ reservoirs. Input parameters are derived from interpretations of borehole images at the Rotokawa and Wairakei geothermal fields where fractures have high dip magnitudes (> 60–70°). This paper focuses on the effect of fracture density along virtual boreholes (P10), that is in average 0.6 m−1 in sheet-like andesites; 0.8 m−1 in ignimbrites and 1.7 m−1 in rhyolite lavas.ResultsThe number of fractures in the models scale linearly with the input P10 in virtual boreholes. The percolation threshold, where the backbone of fractures is connected across the entire model domain, is reached for P10 > 0.24 m−1. Above this threshold, mean flow measured along the mean fracture direction scales linearly with P10. For P10 > 0.4 m−1 the permeability anisotropy lies in the interval 13 ± 3, with the scatter decreasing as P10 increases. The pressure distributions in individual DFN realisations are highly variable, but averages of 50 realisations converge towards those given by equivalent continuum models. Probability density functions resulting from DFN realisations can therefore be used to constrain continuum models. Tracing of fluid particles through the DFN shows that particles can take numerous pathways to define a swath of paths. The travel time of particles over 1 km follows a distribution similar to real tracer tests, with arrivals peaking at 1–2 days and a long tail stretching to over 200 days.ConclusionsThe new codes, calibrated to real measurements of fracture geometries in borehole images of the TVZ, reproduce patterns of flows in fractured geothermal systems. Mean flows and permeability anisotropies derived from the DFNs can be used to improve modelling of flows through fractured geothermal reservoirs using continuum models at a limited computational cost.

Scaling Microseismic Cloud Shape During Hydraulic Stimulation Using In Situ Stress and Permeability

AbstractForecasting microseismic cloud shape as a proxy of stimulated rock volume may improve the design of an energy extraction system. The microseismic cloud created during hydraulic stimulation of geothermal reservoirs is known empirically to extend in the general direction of the maximum principal stress. However, this empirical relationship is often inconsistent with reported results, and the cloud growth process remains poorly understood. This study investigates microseismic cloud growth using data obtained from a hydraulic stimulation project in Basel, Switzerland, and explores its correlation with measured in situ stress. We applied principal component analysis to a time series of microseismicity for macroscopic characterization of microseismic cloud growth in two‐ and three‐dimensional space. The microseismic cloud, in addition to extending in the general direction of maximum principal stress, expanded in the direction of intermediate principal stress. The orientation of the least microseismic cloud growth was stable and almost identical to the minimum principal stress direction. Further, microseismic cloud shape ratios showed good agreement when compared with in situ stress magnitude ratios. The permeability tensor estimated from microseismicity also provided a good correlation in terms of direction and magnitude with the microseismic cloud growth. We show that in situ stress plays a dominant role by controlling the permeability of each existing fracture in the reservoir fracture system. Consequently, microseismic cloud growth can be scaled by in situ stress as a first‐order approximation if there is sufficient variation in the orientation of existing faults.

Pore structure characteristics and impact factors of laminated shale oil reservoir in Chang 73 sub-member of Ordos Basin, China

This research paper focuses on the laminated shale oil reservoir in the third sub-member of the seventh member of Yanchang Formation (Chang 73 sub-member) in the Ordos Basin. The study aims to comprehensively analyze the lithofacies type, micro qualitative and quantitative pore structure parameters, and the main controlling factors of the pore structure in laminated shale. The analysis involves various techniques, including a comprehensive analysis of TOC, rock-eval, X-ray diffraction, polarized light and fluorescence microscope observation, field emission scanning electron microscope observation, and low-pressure N2 adsorption analysis. Based on the sedimentation characteristics, geochemistry, and mineral composition differences, the Chang 73 laminated shale can be classified into three lithofacies types: tuffaceous-organic matter binary laminated shale, clayey-organic matter binary laminated shale, and felsic-clayey binary laminated shale. The pore network consists primarily of organic hydrocarbon generation pressurization fractures, clay mineral felsic intergranular composite pores, and felsic plasmid intergranular pore fracture systems. Mesopores are the most developed pore type. The pore volume and specific surface area increase in the order of “tuffaceous-organic matter”, “clayey-organic matter”, and “felsic-clay”, while the heterogeneity of the pore network gradually weakens, and the roughness of the pore surface enhances. The overall development of organic matter pores is limited, with organic matter-pyrite-clay mineral composite pores being the main components of micropores. The primary intergranular pore system, associated with rigid quartz particles, dominates the mesopores and macropores, and acts as the main framework of the entire pore network. The development of feldspar dissolution pores is limited and contributes minimally to the pore network.

Multi-Fracture Growth Law for Temporary Plugging and Diversion Fracturing of Horizontal Well with Multiple Clusters in Shale Reservoir

Temporary plugging and diversion fracturing (TPDF) is a common method to increase production and efficiency in shale gas reservoirs, but the growth law of diversion fractures and the temporary plugging mechanism are still unclear, which restricts the further optimization of temporary plugging fracturing schemes. Therefore, in this study, a series of simulation experiments of TPDF in a horizontal well with multi-clusters were carried out for the Longmaxi Shale outcrop by using a large true triaxial fracturing system. The laboratory method of “inner-fracture + inner-segment” TPDF with multiple clusters of perforation in horizontal wells was proposed, and the fracture initiation law and control factors, including the number of clusters and the method of perforating, were investigated. The experimental results show that the peak pressures of inner-fracture temporary plugging (IFTP) and inner-segment temporary plugging (ISTP) stages are higher, and the number of diversion fractures and the overall complexity of hydraulic fractures (HFs) are higher when the number of perforation clusters is five. The peak pressures of IFTP and ISTP do not increase significantly under the fixed-face perforating condition compared with the helical perforating, but the pressure profile fluctuates more frequently, the overall HF morphology is more complex, and the number of diversion fractures and transverse hydraulic fractures (THFs) is higher. In addition, the diversion of multi-fractures corresponds to a stage of frequent fluctuations in the wellhead pressure, during which the pressure reaches the peak and drops sharply, indicating the generation of diversion fractures with larger fracture widths that grow toward the surface of the rock sample. The results of the study provide a theoretical basis for the design of TPDF schemes in the laminar-rich Longmaxi Formation shale reservoir.

Investigating Risk Factors and Magnetic Resonance Imaging (MRI)-Based Grading of Subchondral Incomplete Fracture (SIF) of Medial Femoral Condyle.

Subchondral insufficiency fractures (SIF) of the knee joint are prevalent in osteoporosis patients over the age of 55. Early diagnosis of SIF fracture of the medial femoral condyle is crucial for delaying disease progression, early therapy, and potential disease reversal. Magnetic resonance imaging (MRI) is useful in detecting SIF, which is often undetectable on initial radiographs. This study aimed at developing a grading system for subchondral insufficiency fractures (SIF) based on MRI to predict outcomes and evaluate risk factors. In this study, MRI was used to examine SIF risk variables in the medial condyle of the femur to help clinicians diagnose, treat, and delay the condition. A total of 386 patients with SIF from 2019 to 2021 were retrospectively analyzed and divided into 106 patients in the disease group and 280 patients in the control group according to whether they had SIF. The lesion site, meniscus, ligament, and other parameters were evaluated and compared. At the same time, a grading system was introduced to stratify and statistically analyze the size of the lesion area, the degree of bone marrow edema (BME), meniscus tears, and other parameters in the patients. Most SIF were low-grade (LG) fractures, and the predictors of LG and high-grade (HG) fractures included heel tear (P =0.031), degree of medial malleolus degeneration (P < 0.001), advanced age (P < 0.001), and lesion size (P < 0.001). The prognostic factors that showed significant differences between the two groups included age (P =0.027), gender (P =0.005), side (P =0.005), medial tibial plateau injury (P < 0.0001), femoral medullary bone marrow edema (P < 0.0001), medial tibial plateau bone marrow edema (P < 0.0001), meniscus body partial injury (P =0.016), heel tear (P =0.001), anterior cruciate ligament injury (P =0.002), and medial collateral ligament injury (P < 0.0001). This current study proposed an MRI-based grading system for inferior condylar fractures of the femur, in which HG inferior condylar fractures are associated with severe medial malleolus degeneration, advanced age, lesion size (correlation), and meniscus heel tears.

Experimental Investigation of the Fractal-Permeability Properties of Locally Fractured Coal Bodies around Gas Extraction Boreholes

To investigate the permeability characteristics in the in-situ fractured coal body around the perimeter of gas extraction boreholes, the steady-state permeability of fractured coal bodies with different gradations was tested using the fractured rock permeability test system. By controlling the axial displacement and permeability pressure, the permeability parameters were obtained under different porosities. The interactions between the permeability parameters and the process of permeability destabilisation are discussed. The results show that the permeability characteristics of the broken coal body obey the Forchheimer relationship: As the axial displacement increases, the permeability resistance of the fluid increases and the non-Darcy property of the sample becomes more significant. With the decrease in the porosity of the sample and the increase in the power index n, the permeability k decreases and the non-Darcy factor β increases. The final fractal structure of the sample will be changed by particle fragmentation and migration during the loading process of the sample with different levels, and the internal pore structure of the sample will further affect the penetration of the penetration channel. A critical characteristic value for the seepage instability in broken coal bodies is given, and an expression for determining the seepage instability by permeability and non-Darcy factors is proposed. The results indicate that a negative non-Darcy factor is not a necessary condition for permeability instability, and the critical Reynolds number for the permeability instability in broken coal bodies was determined from the perspective of the Reynolds number. The conclusions of this study can provide theoretical support for the theoretical study of permeability and the permeability of pre-smoking coal seams.

Three-Dimensional Simulation of the Fracture System Distribution in Formation Rock Based on Fractal Method

Three-Dimensional Simulation of the Fracture System Distribution in Formation Rock Based on Fractal Method

The geochronology of pegmatites in the Jiajika lithium deposit, western Sichuan, China: Implications for multi-stage magmatic-hydrothermal events in the Songpan-Ganze rare metal metallogenic belt

The Songpan-Ganze orogenic belt is a large-scale rare metal metallogenic belt in western China. Several large-scale granitic pegmatite-type lithium deposits are located in the Songpan-Ganze orogenic belt, which include the Jiajika Li deposit, one of the largest pegmatite-type Li deposits in China. The geochronological constraints of pegmatites and granite in Jiajika are still inadequate for revealing the relationships between mineralization and tectonothermal events. In this study, we performed columbite-group minerals (CGM) and cassiterite U–Pb dating on seven different pegmatite veins with different occurrences and deformation styles in the Jiajika deposit. These pegmatites yield CGM U–Pb ages of 213 to 208 Ma and cassiterite U–Pb ages of 199 to 192 Ma, regardless of their occurrences and deformation. Columbite-group minerals exhibit low Ta# (=Ta/(Ta + Nb)) cores and high Ta# rims, which were formed during the magmatic stage and the hydrothermal stage, respectively. The appearance of cassitertite is closely related with greisenization. Therefore, the CGM U–Pb ages, which were obtained from the low Ta# cores of CGM, are interpreted as magmatic crystallization age, while the cassiterite ages reflect another younger stage of magmatic-hydrothermal event. According to field observation, we consider that the occurrences and deformation of pegmatite veins are controlled by the development of various fracture systems formed during the ascent of the granitic pluton. Our results suggest long-lasting multi-stage magmatic-hydrothermal events in the Jiajika region. Geochronological data of other rare metal deposits located in the Songpan-Ganze orogenic belt and the Western Kunlun orogenic belt are comparable with those of the Jiajika Li ore deposit, indicating that the entire Songpan-Ganze rare metal metallogenic belt experienced long-lasting and multiple magmatic and fluid activities. The overlaps of the geochronological results of granites and pegmatites in the Songpan-Ganze rare metal metallogenic belt suggest that regional magmatism is closely related to Li mineralization. The enrichment of Li in the Songpan-Ganze rare metal metallogenic belt is possibly related to its unique geodynamic setting and the long duration of magmatic-hydrothermal activities.

Determination of heat transfer representative element volume and three-dimensional thermal conductivity tensor of fractured rock masses

The natural fracture system exerts a significant influence on the physical and mechanical properties of rock masses. The heat transfer in fractured rock masses is much more complicated than that of intact rock due to the thermal contact resistance induced by natural fractures with varying size, aperture, roughness, and orientation. This work describes a method for determining the representative element volume (REV) of heat transfer and the 3D thermal conductivity tensor of fractured rock masses. The method is based on the element-wise averaging of temperature and heat flux, which can be obtained from a finite element solution to a steady state heat transfer problem with specific boundary conditions. A case study was conducted based on the geological data of a potential area for high level radioactive waste disposal in China. The results indicate that the size of heat transfer REV of the rock masses in the study area is approximately 18 m × 18 m × 18 m. 3D thermal conductivity tensor, the magnitudes and directions of the three principal thermal conductivities, and anisotropy of the fractured rock masses were obtained. Influences of main fracture parameters including density, disc diameter, and thermal contact resistance on the heat transfer characteristics were investigated. The research results in this work can provide a better understanding of the discontinuous heat transfer processes in fractured rock masses and their homogenization methods.

Regional stratigraphically discordant dolomite mapping based on a dolomitization mechanism on the Arabian carbonate shelf

Dolomite mapping, as a first step of carbonate diagenetic modeling, is critical to understanding dolomitization mechanisms and predicting reservoir quality. Stratigraphically discordant dolomite bodies within the Upper Jurassic intervals have long been studied on the Arabian shelf. Our dolomitization mechanisms find that faults/fractures serve as migration conduits and determine dolomite distribution by controlling fluid flow. We establish an innovative approach based on the diagenetic mechanisms and comprehensive characterization of fracture systems at multiple scales to delineate dolomite in the study area. The complex fracture networks in the subsurface are categorized into macroscale, mesoscale, and microscale fractures. Macroscale fractures, i.e., faults, are much greater than the seismic wavelength and are easily observed in seismic sections due to their obvious seismic discontinuities. Mesoscale fractures are slightly greater than or equal to the seismic wavelength and are recognized using seismic attributes. Microscale fractures are significantly smaller than the seismic wavelength and are observed mainly on core samples and thin sections. The dolomite mapping workflow includes three steps: (1) calibrate the seismic response of multiscale fractures with borehole image logs and core interpretations, (2) implement multiscale fracture characterization using multiple seismic attributes, and (3) interpret dolomite bodies based on fracture characterization and log identification. The mapping results show that massive dolomite bodies are heterogeneously developed and distributed mainly in the northeastern part of the study area, with a southward decrease in dolomite content. The application demonstrates that multiscale fracture systems play critical roles in massive dolomitization, and multiscale fracture prediction provides an innovative solution to delineate complex dolomitization systems and the combination of reservoir and seal in diagenetic traps.

Hydrogeochemical modelling of groundwater in a fractured Carboniferous sandstone aquifer

Deep groundwater monitoring in tight bedrock is not commonly performed and rarely documented. For a case study in Bochum, NRW, deep monitoring wells allow groundwater investigation in the outcropping Carboniferous down to a depth of 186 m. Groundwater monitoring was carried out by combining sampling of the monitoring wells and local springs at the site. Inverse models were developed using the hydrogeochemical code PHREEQC to understand the natural geochemical processes of deep groundwater in the coal-bearing sandstone. The identified hydrogeochemical processes are pyrite oxidation in shallow fracture systems and Na-Ca/Mg cation exchange in deep fracture systems. Core samples reveal fractures containing Fe-dolomite and calcite cements. A freshening process dominates the deep fractured rocks, where fresh water is flushing a saline aquifer. The data presented here support the planning of further monitoring wells and help to improve future modelling approaches.

Poroelastic response of inclined wellbore geometry in anisotropic dual-medium/media

Shale gas formations are typically characterized by anisotropic and fracture properties. Existing shale wellbore stability models have only considered the anisotropy of shale rocks and have ignored the effect of fractures. However, the mechanism of wellbore instability under the combined effects of shale anisotropy and dual-media (DM) remains unknown. Therefore, based on anisotropic poroelasticity, the DM theory, and the assumption of generalized plane strain, this study established a pseudo-3D hydraulic-mechanical coupling finite element model considering the DM and anisotropy of shale in wellbores. The effects of elastic anisotropy, fracture volume fraction, fracture permeability, mass transfer coefficient, and fluid pressure on wellbore stress were analyzed parametrically. The results showed that an anisotropic single-medium predicts that the wellbore will fail when the formation is drilled, whereas an anisotropic DM predicts periodic wellbore instability. The poroelastic effect of the matrix pore pressure is much greater than that of the fracture pore pressure. The matrix elastic anisotropy parameters control the distribution of mechanical parameters throughout the DM, further affecting the poroelastic response of the entire DM. When the drilling direction was mostly parallel to the bedding plane, the anisotropy of the matrix and fracture system of the elastic parameters were larger, and the wellbore was more stable. A larger fracture permeability leads to a larger fracture volume fraction and mass transfer coefficient, the matrix pore pressure and fracture pore pressure increase, and the instability of the wellbore also increases.

Open fractures of the hand: a new classification based on risk score to predict infection requiring re-debridement.

We developed a classification for open hand fractures based on risk score to predict the risk of infection requiring re-debridement. A total of 846 retrospectively included patients underwent multivariable analysis with backward elimination to derive the predictive risk score from independent predictors. The incidence of infection requiring re-debridement was 4%. Independent predictors include diabetes mellitus or immunocompromised condition, injuries from a bite, fractures with comminution/bone loss, neurovascular injuries and inadequate soft tissue coverage. The area under the receiver operating characteristic curve of the prediction score was 0.79. The new classification system for open hand fractures divides patients into three groups: low-risk open fractures (Type I, score <1); moderate-risk open fractures (Type II, score 1 to 2.5); and high-risk open fractures (Type III, score >2.5), based on the risk of infection requiring re-debridement. Re-debridement and delayed primary closure are suggested for type III open fractures.Level of evidence: III.

Multiscale Fine Characterization of a Coal Pore–Fracture System Based on SEM, CT, and NMR in the Jingbian Block, Ordos Basin

To achieve an accurate and comprehensive characterization of the multiscale pore–fracture characteristics of Permian coal in the Jingbian Block, Ordos Basin, a combination of scanning electron microscopy (SEM), X-ray computed tomography (CT), and nuclear magnetic resonance (NMR) techniques was utilized. With these experiments, the mineral composition, pore size distribution (PSD), porosity, and connectivity of pores in coal samples were characterized through qualitative and quantitative methods. The results show that the SEM experiments enabled qualitative identification of pores and mineral types. The coal samples primarily contained gas pores, cell pores, intercrystalline pores, and moldic pores, and clay minerals were the predominant fracture fillings. The 3D reconstruction of the CT experiments shows that the pores and fractures generally expand horizontally, while the minerals show obvious bedding expansion characteristics. Moreover, the estimation of full-size porosity in coal samples can be achieved by combining CT and NMR experiments. The full-size porosity of samples G11-5-1, G11-5-6, G11-5-9, and G11-5-11 was 8.93%, 9.11%, 10.45%, and 11.63%, respectively. The connectivity differences are primarily determined by the throat development degree and the connected pore–fracture count. Samples with more connected pores and larger throat radii exhibit excellent connectivity.

Cutting Performance and Wear Mechanism of Multilayer Diamond‐Coated Tools

Monolayer and multilayer diamond films are deposited on WC‐Co cemented carbide by hot‐filament chemical vapor deposition. The growth characteristics of diamond coatings are analyzed. Cutting performance characteristics such as tool life and the stability of machining process in the machining of presintered ZrO2 are compared based on the variation of cutting speed and resultant cutting force, and workpiece surface roughness. For the monolayer diamond coatings, as the concentration of CH4 increases from 1% to 5%, the diamond crystal is transformed from micron columnar crystal to nanocluster crystal. The multilayer diamond coatings combine the advantages of micron‐ and nanocrystalline structures. The multilayer diamond‐coated tool exhibits longer service life and better machining quality. Because of the appearance of the brittle–plastic conversion mechanism, the surface integrity of ZrO2 processed by multilayer diamond‐coated tool is relatively high. As for the uncoated tool, the workpiece is mainly machined by brittle spalling. The interfacial stratified fracture system between the interlayers is proposed to be the toughening mechanism of the multilayer structure.

Characteristics and Geological Impact Factors of Coalbed Methane Production in the Taiyuan Formation of the Gujiao Block

The coalbed methane resources of the Gujiao Block are abundant, and the exploration degree is high. The gas production and water production of different CBM (coalbed methane) wells vary greatly. The average gas production of CBM wells in the study area is mostly less than 1000 m3/d, while the average water production is mostly less than 5 m3/d. The gas production of CBM wells near the core of the Malan syncline is relatively high. A series of large faults exist in the central and eastern parts of the study area, and CBM wells nearby produce more water but less gas. The salinity of water discharged from CBM wells ranges from 810.34 to 3115.48 mg/L, which is consistent with the trend of a gradual increase from north to south. The gas content distribution follows this same gradually increasing north to south trend. Coal thickness and buried depth have little effect on gas production, but have some effects on water production. The endogenous fracture system in the coal reservoir is extremely developed and the porosity and permeability of the reservoirs are low, which is not conducive to the migration and recovery of coalbed methane. The adsorption capacity of the coal sample is strong. However, the continuous uplift and denudation of the stratum from the middle Yanshanian to the Himalayan region are not conducive to the preservation and enrichment of coalbed methane. In addition, a series of large faults exist in this area, and the coal structures are broken. A large amount of coalbed methane is continually being released. Generally, structural and hydrological conditions affect the porosity, permeability, and gas content of coal reservoirs, thereby affecting the productivity of coalbed methane wells. The comprehensive analysis shows that the Xingjiashe well field in the southern part of the study area is a favorable area for CBM exploration and development.

Numerical Investigation of the Structure of Fracture Network Impact on the Fluid Flow through a Poroelastic Medium

Two-dimensional single-phase flow of a weakly compressible fluid through a deformable fractured-porous medium is considered. A poroelastic model is used for coupled simulation of the fluid flow and the related changes in the stress state of the medium. Fracture network is simulated using the discrete fracture model. The fractures in the region under consideration have random location and orientations, and the fracture length distribution follows a power law. The dependence of the hydraulic properties of fractured porous media on its stress-strain state and the structure of the fracture network is studied. Numerical study was performed for various realizations of fracture network obtained using multiple random generation. It is found that the permeability of the fractured porous medium is determined mainly by the structure of the fracture system characterized by the percolation parameter. According to the simulations results, hydraulic properties are significantly affected by the stress-strain state only for connected fracture systems. An approximation is proposed to define the dependence of the equivalent permeability of a fractured-porous medium on the following parameters: the connectivity of the fracture system, the stress-strain state of the medium, and fracture properties such as stiffness and aperture.