Search

El uso de la Tomografía Computarizada de Haz Cónico (CBCT) ha sido ampliamente relevante en el campo de la Endodoncia, pues además de que permite la visualización en los diferentes cortes (axial, coronal y sagital), facilita la emisión de diagnósticos más precisos como fracturas radiculares y/o coronales, reabsorciones radiculares, periodontitis apical en estadios iniciales, perforaciones, planificación de cirugías endodónticas, entre otros. Objetivo: Determinar la sensibilidad y especificidad de la CBCT en la detección de fractura vertical mediante la revisión sistemática. Métodos: Se realizó una revisión sistemática, en la cual se tuvieron en cuenta estudios realizados entre los años 2012 a 2022. Se utilizaron las bases de datos Pubmed y Springer, incluyendo artículos en inglés y español disponibles en forma completa. Se utilizaron artículos relacionados con Efectividad y sensibilidad de la CBCT en los hallazgos de fractura vertical. Resultados: En esta revisión se identificaron 176 documentos. Luego de revisar los títulos, resúmenes y palabras clave, se descartaron 78, pues no trataban sobre Efectividad y Sensibilidad de la CBCT o estaban duplicados. De estos se descargaron 108 artículos para ser examinados con mayor profundidad por medio de la lectura del texto completo, de los cuales se descartaron 87 debido a que no eran estudios in vivo, in vitro o por no estar dentro del rango de año de publicación establecido. Finalmente, el número de artículos de texto completo evaluados para su elegibilidad fueron 21. Conclusiones: El uso de CBCT en el diagnóstico de fractura vertical es una herramienta útil, pero se debe tener conocimiento de la configuración del equipo para poder ser lo más preciso posible, utilizar tamaños de voxel menores a 2 micras, para evitar la pérdida de sensibilidad y especificidad. The use of Cone Beam Computed Tomography (CBCT) has been very relevant in the field of Endodontics, since in addition to allowing visualization in different cuts (axial, coronal and sagittal), it facilitates the issuance of more precise diagnoses such as root and/or crown fractures, root resorptions, apical periodontitis in early stages, perforations, endodontic surgery planning, among others. Objective: To determine the sensitivity and specificity of CBCT in the detection of vertical fracture through systematic review. Methods: A systematic review was carried out, in which studies carried out between the years 2012 and 2022 were taken into account. The Pubmed and Springer databases were used, including articles in English and Spanish available in full. Articles related to the Effectiveness and Sensitivity of CBCT in the findings of vertical fracture were used. Results: In this review, 176 documents were identified. After reviewing the titles, abstracts and keywords, 78 were discarded, since they were not analyzed on the Effectiveness and Sensitivity of the CBCT or they were duplicated. Of these articles, 108 were downloaded to be examined in greater depth by reading the full text, of which 87 were discarded because they were not in vivo or in vitro studies or because they were not within the established publication year range. . Finally, the number of full-text articles evaluated for eligibility was 21. Conclusions: The use of CBCT in the diagnosis of vertical fracture is a useful tool, but knowledge of the equipment configuration must be known in order to be as accurate as possible. , use a voxel size smaller than 2 microns, to avoid loss of sensitivity and specificity. Especialista en Endodoncia http://www.ustabuca.edu.co/ustabmanga/presentacion Especialización

Summary Proppant placement plays a crucial role in maintaining the conductivity of fractures after a hydraulic fracturing treatment. The process involves the transport of particles by fluid flow in complex fractures. Many studies have focused on proppant transport and distribution in the fracture with a constant aperture, but relatively few studies have investigated the proppant-fluid flow in a vertical fracture with a contracted aperture. In this work, we examine experimentally proppant transport in a fracture with a contracted aperture. The objective is to evaluate the distribution of particle beds in the contracted fracture at different flow conditions. In this paper, particle-fluid flow in the contracted fracture is studied experimentally by a laboratory size slot. A planar slot with a constant width is used to benchmark the experimental results, and a published correlation validates the bed equilibrium heights in the planar slot. Six types of particles are chosen to simulate the effects of particle density and size. The proppant distribution is evaluated by the bed height when the bed reaches the equilibrium states. The effects of fluid velocity, fluid viscosity, particle density, particle size, and particle volume fraction on particle distribution are investigated. The results confirm that the proppant particle-fluid flow in the contracted slot is more complicated than that in the planar slot. The phenomena of particle vortices and resuspension were observed at the contraction of the cross-section. The shape on the top of the bed is like a descending stair in which the height gradually decreases in the length direction. The bed height in the contracted slot is lower and more irregular than that in the planar slot at the same flow conditions. Smaller sands injected at a high flow rate and fluid viscosity can form a lower bed. The trend would be reversed by using denser particles and high particle volume fraction. A reliable model expressed by four dimensionless numbers is developed by the linear regression method for predicting the bed equilibrium height. The model and experimental results provide directions to quantitatively evaluate the particle transport and distribution in a fracture with a contracted aperture.

We have studied by classic anatomical methods the presumed cranium of Sampiero Corso (1498-1567), who was the first Corsican nationalist. This cranium corresponds to that of a male individual, aged at least of 50 years ; there are many similarities between the cranium face and the one that corresponds to his portrait. The vertical fracture, observed on the cranium left side of the forehead, corresponds probably to the stab sword that caused Sampiero Corso’s death. The 14C radiodating of a bone fragment located at the cranium basis gives a calendar 1450-1510 years interval (at 95% of probability) of age.

Hydraulic fracturing, as a key technology of deep energy exploitation, accelerates the rapid development of the modern petroleum industry. To study the mechanisms of hydraulic fracture propagation and rock failure mode of the vertical well hydraulic fracturing, the true triaxial hydraulic fracturing test and numerical simulation are carried out, and the influence of the principal stress difference, water injection displacement, perforation angle and natural fracture on fracture propagation is analyzed. The results show that the fracture propagation mode of limestone is mainly divided into two types: the single vertical fracture and the transverse-longitudinal crossed complex fracture. Under high displacement, the fracturing pressure is larger, and the secondary fracture is more likely to occur, while variable displacement loading is more likely to induce fracture network. Meanwhile, the amplitude of acoustic emission (AE) waveform of limestone during fracturing is between 0.01 and 0.02 mV, and the main frequency is maintained in the range of 230–300 kHz. When perforation angle θ=45°, it is easy to produce the T-type fracture that connects with the natural fracture, while X-type cracks are generated when 0=30°. The results can be used as a reference for further study on the mechanism of limestone hydraulic fracturing.

The purpose of this study was to characterize the patterns of lingual split and lateral bone cut end (LBCE) after bilateral sagittal split osteotomy (BSSO) in patients and identify their associations with postoperative neurosensory disturbance. This retrospective cohort study recruited 273 patients with skeletal malocclusion who received BSSO. The postoperative cone beam computed tomography data were reconstructed to three-dimensionally view the patterns of lingual split and LBCE. Associations between lingual split and LBCE and their effects on neurosensory disturbance in the lower lip and chin were determined. Six types of lingual split and three types of LBCE were defined based on three-dimensional images. Type I lingual split as a vertical fracture line to the inferior mandibular border was the most common (40.29%). Inferior LBCE was the most prevalent, followed by lingual and buccal types. Significant associations among lingual split, LBCE and skeletal deformities were found (P 0.05). However, patterns of lingual split and LBCE were not associated with the incidence of neurosensory disturbance. Patterns of lingual split after BSSO significantly associated with types of LBCE and dentomaxillofacial deformities, but not with postoperative neurosensory disturbance.

Hydraulic fracturing has been demonstrated to be a cost-effective method of developing low-permeability heterogeneous clastic reservoirs with vertical wells. In the presence of a thin shale layer as a seal, monitoring effective fracture height becomes extremely important. The conventional approach of a single-regime production logging may be ineffective due to the complex geometry of fluid flow in the near-wellbore zone around the well. The paper describes the experience of the multi-rate through barrier diagnostics as a method of improving hydraulic fracturing evaluation. The standard way to diagnose the effectiveness of hydraulic fracturing is to log a survey under current operating conditions. In general, temperature and passive spectral acoustic measurements provide useful information on identifying the boundaries of fluid movement behind production casing; however, it is difficult to determine if flow occurs in the vertical hydraulic fracture or channeling through damaged cement in a single-regime survey. The multi-rate through-barrier diagnostics allow analyzing the flow dynamics of the wellbore-fracture-formation system under different flowing regimes, enabling a more accurate assessment of fluid movement in the near-wellbore environment within several meters. The paper includes the results of the multi-rate logging survey campaign in vertical water injection wells drilled in a low-permeability clastic reservoir. A proppant-based hydraulic fracturing of the target formation was carried out in the wells. The geological structure of the developed reservoir includes a thin shale layer (break) that separates the target oil-saturated interval from the overlying water bearing reservoir. In order for the operator to optimize future stimulation programs identification of effective hydraulic fracture height in reservoir regions with different shale thicknesses is crucial. The upper boundaries of the injected fluid movement behind the casing were determined based on the survey results. Analysis of the acoustic and temperature field dynamics helped more reliably evaluate the nature of the fluid movement behind the casing, whether flow happens in vertical fracture or cement channeling. This results in a more precise quantitative assessment of the injection profile in the targeted and untargeted reservoir units.

Gravity displacement often occurs when drilling a vertical fractured formation, causing a downhole complexity with risk of blowout and reservoir damage, well control difficulty, drilling cycle prolongation, and increased costs. Based on an experimental device created for simulating the gravity displacement, various factors affecting the displacement quantity were quantitatively evaluated by simulating the fracture width, asphalt viscosity, drilling fluid density, and viscosity under different working conditions, and a liquid–liquid displacement law was obtained. Using the theories of rock mechanics, fluid mechanics, and seepage mechanics, based on conformal mapping, as well as a fracture-pore double substrate fluid flow model, we established a steady-state mathematical model of fractured formation liquid–liquid gravity displacement by optimizing the shape factors and using a combination of gravity displacement experiments to verify the feasibility of the mathematical model. We analyzed the influence of drilling fluid density, fracture height and length, and asphalt viscosity on displacement rate, and obtained the corresponding laws. The results show that when the oil–fluid interface is stable, the fracture width is the most important factor affecting the gravity displacement, and plugging is the most effective means of managing gravity displacement.

At present, the hydraulic fracture technologies are widely used for intensification of oil and gas recovery from reservoirs with hard-to-recover reserves. The simulation of the processes of flow through porous reservoirs with hydraulic fractures is fairly completely developed in the steady-state flow approximation. Unsteady processes of pressure distribution are considered with reference to the theory of hydrodynamic methods of investigations of wells in which asymptotically limited intervals of variations in the coordinates and time, i.e., the distances of the order of the well radius and time much smaller than the characteristic time of the process of flow through the porous medium, are considered. At the same time, in the reservoirs with hard-to-recover reserves (low-permeability reservoirs and high-viscosity oils) the duration of the unsteady processes of pressure redistribution can be of the same order as the characteristic time of flow through the reservoir. In the present study new analytical solutions of the problem of unsteady pressure redistribution in the neighborhood of a well penetrated by a vertical fracture are given. The scientific novelty of the study consists in the fact that, firstly, the fluid compressibility in the fracture and, secondly, the fluid flow not only through the fracture but also through the porous reservoir are taken into account in the model used. The solutions of the problems are constructed using the Laplace transform technique. In particular cases, the expressions well-known in literature follow from the solutions obtained. The analytical solutions obtained which makes it possible to determine the main characteristic features of the processes of flow through a porous medium are analyzed.

The linear slip theory is gradually being used to characterize seismic anisotropy. If the transversely isotropic medium embeds vertical fractures (VFTI medium, according to Schoenberg and Helbig, 1997), the effective medium becomes orthorhombic. The vertical fractures may exist in any azimuth angle which leads the effective medium to be monoclinic. We apply the linear slip theory to create a monoclinic medium by only introducing three more physical meaning parameters: the fracture preferred azimuth angle, the fracture azimuth angle and the angular standard deviation. First, we summarize the effective compliance of a rock as the sum of the background matrix compliance and the fracture excess compliance. Then, we apply the Bond transformation to rotate the fractures to be azimuth dependent, introduce a Gaussian function to describe the fractures’ azimuth distribution assuming that the fractures are statistically distributed around the preferred azimuth angle, and average each fracture excess compliance over azimuth. The numerical examples investigate the influence of the fracture azimuth distribution domain and angular standard deviation on the effective stiffness coefficients, elastic wave velocities, and anisotropy parameters. Our results show that the fracture cluster parameters have a significant influence on the elastic wave velocities. The fracture azimuth distribution domain and angular standard deviation have a bigger influence on the orthorhombic anisotropy parameters in the (x2; x3) plane than that in the (x1; x3) plane. The fracture azimuth distribution domain and angular standard deviation have little influence on the monoclinic anisotropy parameters responsible for the P-wave NMO ellipse and have a significant influence on the monoclinic anisotropy parameters responsible for the S1- and S2-wave NMO ellipse. The effective monoclinic can be degenerated into the VFTI medium. Assuming that the fracture cluster has a preferred azimuth angle and other fractures are statistically distributed around it, we define the effective compliance matrix by a Gaussian function, the Bond transformation matrix and the excess compliance matrix of the vertical fractures in the eigen-coordinate system. The resulting effective medium possess the monoclinic symmetry. The monoclinic anisotropy parameters (Stovas, 2021) can easily be defined from the effective stiffness coefficients. Schoenberg, M. and Helbig K., 1997, Orthorhombic media: Modeling elastic wave behavior in a vertically fractured earth, Geophysics, 62(6), 1954-1974.Stovas, A., 2021, On parameterization in monoclinic media with a horizontal symmetry plane, Geophysics (early online).

Objectives: Condyle fractures constitute 17.5–52% of all mandibular fractures. Our first aim was to investigate whether panoramic radiography or LSP images with lower radiation dose can be used instead of CBCT in the diagnosis of vertical condylar fractures. The second aim of the study was to compare observers' capabilities in diagnosing these fractures. Materials and Methods: A sample consisting of 15 fresh cadaver mandibles with 30 condyles frozen within 24 hours post-mortem was randomly selected. Vertical fractures from the lateral 2/3 of the condyle head with 0.5 (10 condyles) and 1mm (10 condyles) thickness were created using a fret saw. After creating condyle fractures, digital panoramic, LSP, and CBCT images were acquired. Two dentomaxillofacial radiologists with 15 years of experience, two dentomaxillofacial radiologists with five and seven years of experience, and two newly graduated dentists have evaluated the images. The success of the observers in diagnosing the vertical condyle fracture in each imaging method, intra-observer and inter-observer agreement was evaluated. Results: The success of all dentists in determining the condyle fractures using LSP images was higher than the success they achieved using panoramic images, but it was not sufficient. Using different imaging options with CBCT, all diagnoses made by new graduates and dentomaxillofacial radiologists with five and 15 years’ experience were 100% compatible with the gold standard (AC1: 1 (1–1)). Conclusions: For the diagnosis of vertical condyle fractures, conventional techniques (panoramic and lateral jaw imaging methods) were found to be insufficient.

The purpose of this paper is to provide scientific basis for the stability evaluation of overburden rock of repeated mining goaf under the expressway. The objectives of the present study are to reveal the development of overburden rock fractures under repeated mining and to identify the fractal characteristics of the overburden rock fractures. The results show that (1) the separation fracture and vertical fracture fissure are developed in the overburden rock under repeated mining; (2) after the mining of the lower coal seam, the fractures developed in the overburden rock of the goaf are obviously retained in general. The number of fractures on both sides of the goaf is relatively large, while in the central part, it is relatively small and the fractures in most areas are basically closed; (3) under the same advancing length of working face in the lower coal seam, the fractal dimension in the caving zone is larger than that of the fractured zone; (4) with the increase of the advancing length of working face in the lower coal seam, the variation trend of the fractal dimension appears from small to large and then to small and stable; (5) when the repeated mining is over and the overburden rock movement is basically stable, the ratio of the fractal dimension in the caving zone and the fractured zone is 1.067:1. The results have an important reference value for ensuring the safety of the expressways above the repeated mining goaf in Shanxi region and similar areas.

Fracturing is the dominant stimulation technology for low-permeability reservoirs. In recent years, thin and poor reservoir has gradually become the main potential exploration object.And thin and poor reservoirs are often accompanied by thin interlayer. For the thin and low strength interbedded reservoirs, it is difficult for commingled fracturing to ensure each layer is improved and thus subdivided layer fracturing is needed. However, this kind of subdivided layer fracturing also has to face the problem of cross-flow which may result in failed fracturing or even serious water out. A large of statistics show that cross-flow often takes place on the contact surface of cement ring and formation as well as in the interlayer.In this paper, the minimum horizontal geostress profile of reservoir is calculated by rock mechanics theory under the condition of fracturing vertical fracture. And the distribution of minimum horizontal stress is approximately proportional to the distribution of natural gamma. Based on this, field test is carried out. So the fracturing boundary relationship of thin interlayer Wells in Y oilfield is given under the existing fracturing technology. According to this condition, we can decrease the probability of interlayer cross-flow by fracturing control. Moreover, cross-flow on the contact surface can be avoided to the most extent by estimating the quality of well cementation using Ciflog-geospace software. Finally, these optimization methods are proved effective and correct by field trial and thus greatly boost the success rate of subdivided layer fracturing.

The depletion of producing layers leads to significant stress changes in adjacent targets, especially when complex natural fractures are present. Due to weak bedding interfaces or small stress barriers, hydraulic fractures can easily penetrate neighboring layers, and this further increases the chance of multilayer stress disturbance. In this work, we investigate the effects of vertical fracture complexity, i.e., hydraulic fracture penetration and interlayer natural fracture existence, on stress interference between different layers using a data set from a typical shale gas well in the Sichuan Basin. Two geological contexts, i.e., without interlayer natural fractures (w/o INF) and with interlayer natural fractures (w/ INF), are considered under different degrees of fracture penetration and interlayer connectivity. An in-house iteratively coupled geomechanics and compositional reservoir simulator is used to model the three-dimensional pressure and stress changes. The non-uniform hydraulic fractures and stochastic natural fractures are incorporated in our coupled simulation with an embedded discrete fracture model (EDFM). Comprehensive spatial-temporal stress analysis quantifies the approximate range of orientation change of SHmax and magnitude change of Shmin under various reservoir conditions. Numerical results indicate that the presence of natural fractures in the interlayer upgrades the risk of stress interference between different pay zones. A larger hydraulic fracture penetration increases gas production, but also exerts a significant impact on stress reorientation and redistribution in the upper potential layer. The orientation change of SHmax along the prospective infill location is below 10 degrees in the w/o INF cases but up to 30 degrees in the w/ INF cases with a moderate number of interlayer natural fractures. The average magnitude change of Shmin is within 3.5 MPa along the prospective infill location for most w/o INF cases, whereas that in the w/ INF cases is above 10 MPa at most times. Moreover, the existence of natural fractures in the interlayer brings forward the occurrence of maximum orientation change in the upper layer by around one year. While inducing non-negligible stress drop in the upper layer, higher interlayer matrix permeability does not significantly reorient the horizontal principal stresses. Varying the density of interlayer natural fractures not only affects the stress magnitude but also causes considerable orientation change in the upper layer. The findings from this work help understand the extent of stress interference in the upper potential layer of the Sichuan Basin under different vertical fracture complexities. It is of guiding significance for future hydraulic fracture design and child-well operations in similar highly fractured tight formations.

Solute transport in a single vertical fracture (SVF) cannot be reliably described by the classical advection-dispersion equation (ADE) model, due to the heterogeneity nature of fracture. This study conducted a group of experiments to investigate chloride ion transport in the SVFs under different rough-walled conditions, and then applied a time fractional advection-dispersion equation (F-ADE) model to offer an accurate description. A comparison between F-ADE model and a classical ADE model in describing experimental data, was also carried out. Results show that the FADE model is better than the ADE model in describing the breakthrough curve and heavy-tail phenomenon of solute transport in the fracture. Especially in the experiments with lower flow rate and higher roughness fracture, the FADE model can offer a better description for non-Fickian transport, indicating that it is a promising tool for characterizing solute transport heterogeneous vertical fracture.

Hydraulic fracturing is an important technology to improve oil and gas production. In recent years, rod-shaped proppant has received increasing attention for its advantages in avoiding fracture closure and enhancing conductivity. Due to its special shape, the settling process in the fracture is more complicated than that of a spherical proppant. Accurate description of the wall factor of fracture on the settling rod-shaped proppant is pivotal in predicting the transport distance of rod-shaped proppant and improving the effect of fracturing. However, few researches have been reported about the fracture wall factor on the settling rod-shaped proppant. In this study, the transparent fracture model with different width and a high-speed camera were used to record the settling process of the rod-shaped proppant in the fracture. A total of 215 tests were carried out to analyze the effects of fluid properties, the equivalent dimensionless diameter, sphericity, and Reynolds number on the wall factor, involving the ranges of the equivalent dimensionless diameter and the particle Reynolds number are 0.03 to 1.47 and 0.03–1354.14, respectively. The settling processes of rod-shaped proppant under horizontal and vertical states were studied, and two wall factor models for the two states were established, respectively. The results show that the wall factor is a function of both the equivalent dimensionless diameter and Reynolds number. Finally, the prediction models of wall factor with the prediction error of 1.70 and 4.44% are established for these two Reynolds number regions, respectively. The results of this study can further improve the performance of rod-shaped proppant in hydraulic fracturing.

This paper evaluates the axial compressive behaviour of concrete stub columns confined by steel tubes (CSC-CSTs) at low temperatures of 30 ~ −80 °C relevant to cold regions. Experiments including ten circular and ten square CSC-CSTs subjected to axial compression at four low temperatures were carried out. The studied parameters included low temperature (T), different grades of NWC (fc), wall-thickness of the steel tube (t), and height of the CSC-CSTs (L). The test results revealed that bulge of steel tubes, concrete crushing, and vertical fracture in steel tube (only in square CSC-CSTs) occurred to CSC-CSTs. The load-shortening (P S) behaviour of CSC-CSTs exhibits similar manner in the first elastic and nonlinear working stage, but varies at their recession stages due to different confinement ratio by steel tube. Low temperatures improved axial compressive behaviours of CSC-CSTs. Increasing concrete strength improved the compressive strength of CSC-CSTs at low temperatures, but reduced their ductility. Thicker steel tube improved the P S behaviour of CSCCSTs at low temperatures whilst the height of CSC-CSTs exhibited marginal influences on their low-temperature compressive behaviours. Theoretical models were developed to estimate P S behaviours of CSC-CSTs, and validations against 20 test results confirmed their accuracy.

The instability of polymeric membranes with nano- and micro-sized apertures has been regarded as one of the main reasons behind realizing ultra-thin membranes with apertures. As is well known, when the thickness of the membrane gets thinner or the aperture size gets smaller, the possibility of geometrical deformation or structural damage by collapse or fracture increases. Herein, we suggest the design rules for the stability of polymeric membranes possessing 1D nano-line patterns monolithically constructed on micro-aperture supporting layers. The proposed theoretical model, which has been thoroughly demonstrated and analyzed based on both theoretical and experimental approaches, provides stability criteria for lateral collapse and vertical fracture of ultra-thin membranes with apertures.

The aim of this study was to establish an effective method of locating and negotiating the lingual canal in mandibular first premolars with two canals during root canal preparation. A total of 125 mandibular first premolars with radicular grooves were collected, and after micro-computed tomography scanning, 50 mandibular first premolars with a Vertucci V/III canal form were selected based on the inclusion criteria. Access cavities were prepared, and the lingual canals (LCs) were searched in four following steps: step 1 direct vision and a straight K-file; step 2 stereomicroscopy and a straight K-file; step 3 stereomicroscopy and a pre-curved K-file; and step 4 a long-neck bur. After localization, the LCs were instrumented. In most cases, access to the LC was achieved by step 2 (19/50, 38%) or step 3 (22/50, 44%). In three cases (6%), step 1 alone was enough to achieve access to the orifice, and in six cases (12%), access to the lingual canal was not achieved until step 4. Overall, 43 of the 50 mandibular first premolars (86%) were successfully instrumented, and the remaining seven failed. Two cases failed in the process of negotiating the canal to full length and five cases failed due to procedural errors (ledge formation, canal perforation, vertical fracture, or instrument separation). The LC in mandibular first premolars is a major endodontic challenge. A stereomicroscope and a pre-curved K file are suggested to be valuable tools for detecting and accessing the extra LC.