Perforation Length Research Articles

<p><strong>Seed micromorphology of representatives of holoparasitic Orobanchaceae genera from the Caucasus region and its taxonomic significance</strong></p>

Obligate parasitic plant species from the Orobanchaceae family belong to the most critical genera of world flora. Due to their strongly reduced vegetative organ architecture, there arise many difficulties and mistakes in species identification, and extra characteristics of systematic importance are required. Seed micromorphology is a highly informative taxonomic criterion that helps to resolve ambiguities in plant taxonomy and evolution, and has proved to be a valuable complementary tool for Orobanchaceae species identification. In this study, seeds of 43 holoparasitic species from the Cistanche, Diphelypaea, Orobanche and Phelipanche genera collected in the Caucasus were subjected to micromorphological analysis. The Caucasus is one of the most important centres of world biodiversity, with many endangered and endemic parasitic plants. Twenty two quantitative/qualitative micromorphological seed parameters were analysed using stereo ZOOM, confocal scanning laser (CLSM) and scanning electron (SEM) microscopy. Three types of seed were established based on periclinal wall ornamentation: 1) clearly pitted sculpturing in all Cistanche, Diphelypaea, and most Orobanche seeds; 2) fibrillar and veined sculpturing in Phelipanche seeds; and 3) smooth, granular or rugged (very rarely visibly pitted) outer periclinal wall in O. coerulescens and O. colorata seeds. However, CLSM, used in present studies for Orobanchaceae seeds for the first time, revealed more details of wall lignification and ornamentation invisible in SEM images. The best micromorphological characteristics for species identification are the type of ornamentation of the periclinal wall, the width of anticlinal wall, the character of perforation, perforation length and width, the fibrillar character, and fibrillar and vein width. A comparison of the main characteristics distinguishing the seeds of Orobanchaceae is also presented and discussed.

Comparative evaluation of the effect of various irrigants and dry canal on electronic apex locators in locating simulated root perforations: an in vitro study

Objective: this study aimed to evaluate the effects of irrigants and dry canal on the accuracy of electronic apex locator (EAL) in locating simulated root perforations. Material and methods: twenty singlerooted, mandibular premolars were decoronated at CEJ, and the contents were removed with a barbed broach. The canals were instrumented up to a size of 15 K-file. The roots were artificially perforated at 4 mm from the anatomic apex. The actual length (AL) up to the perforation site was determined. The electronic length (EL) of perforations was obtained by Root ZX mini and iRoot in the dry canal and in the presence of 5.2% NaOCl, SmearOff, and 0.9% sodium chloride using a size 20 K-file. The differences between the EL and AL of the perforations were calculated. Statistical analyses using Friedman and Wilcoxon signed-rank tests were used to analyse the data with the level of significance set at p < 0.05. Results: there were significant differences in different canal conditions with both Root ZX mini and i Root. Measurements in dry canals were significantly longer for both apex locators (p < 0.05). Measurements with NaOCl were significantly shorter for both apex locators (p < 0.05). Both apex locators produced significantly accurate values for Saline and Smear OFF (p < 0.05). Conclusions: in this study, both Root ZX mini and i Root were affected by different canal conditions. The most accurate measurements were seen in the presence of saline and SmearOFF.KEYWORDS Electronic apex locator; I Root; Perforation; Root ZX mini; SmearOFF; Sodium hypochlorite; Saline.Keywords: Electronic apex locator, i Root, perforation, Root ZX mini, SmearOFF, sodium hypochlorite, saline

Optimisation of hydraulic fracturing parameters based on cohesive zone method in oil shale reservoir with random distribution of weak planes

Hydraulic fracturing technology plays a key role in the in-situ exploitation of oil shale. A mechanism for generating complex fracture networks in oil shale reservoirs with randomly distribution weak planes is of vital importance to hydraulic fracturing design. In this study, the cohesive zone method (CZM) was adopted to establish a reservoir model with randomly distributed weak planes. Furthermore, the concept of “reservoir reconstruction efficiency (RRE)” was proposed as an index to evaluate the results of hydraulic fracturing. Using the proposed model and orthogonal test, we found that the flow rate has the most significant influence on the RRE, followed by the perforation direction and perforation length. For the simulated reservoir, a flow rate of 0.008 m³/s and perforation direction consistent with the maximum principal stress were the optimal fracturing parameters. Moreover, numerous radial branch fractures were generated under extremely high flow rate. The findings of this study are expected to provide significant help in predicting the fracture propagation and optimising the fracture parameters in oil shale exploitation.

Dynamic fracture propagation model for oriented perforation steering fracturing in low permeability reservoir based on microelement method

Oriented perforation steering fracturing technology with the purpose of enlarging fracture extension scale and increasing reservoir reconstruction volume is a common method for stimulating and reforming low permeability oil and gas reservoirs. Accurate prediction of the fracture deflection trajectory is the key to successful implementation of this technology. Based on the relevant theories of elastic fracture mechanics and the microelement method, a prediction model for the fracture deflection trajectory of steering fracturing is established by comprehensively considering the influences of horizontal in situ stress difference, perforation parameters, injection parameters and formation mechanics parameters. The model completes the cyclic iteration calculation between the minor increment and the propagation direction angle of the crack tip using the calculation program compiled by Visual Basic and realizes the simulation of the dynamic propagation of steering fractures. Taking the tight sandstone reservoir of the Shihezi Formation in Linxing block as an example, the differences between the hydraulic fracture trajectory calculated by this model and the extended finite element model and the micro-seismic monitoring values in the fracturing field were compared, and the influence of various factors on the deflection distance of the hydraulic fracture trajectory were studied. The results show that, compared with the XFEM model, the hydraulic fracture trajectory simulated by this model has better matching with the micro-seismic monitoring results. The deflection distance decreases negatively logarithmically with increasing horizontal in situ stress difference and increases linearly with increasing fracturing fluid displacement and viscosity. The larger the perforated angle, the longer the deflection distance, and the length of perforation has little effect on the deflection distance. The model and conclusions are significant to further understand oriented perforation steering fracturing.

Experimental study of premixed hydrogen-air flame quenching in a channel with the perforated plate

The effect of the perforated plate on the premixed hydrogen-air flame quenching was experimentally investigated with various perforated plate lengths and initial pressures in a channel. The perforated plate has the same cross-sectional area and five lengths in the range of 20 mm, 40 mm, 60 mm, 80 mm and 100 mm. High-speed Schlieren photography was used to track the flame evolution, and correspondingly the flame front speed was calculated. Two piezoelectric pressure sensors were mounted upstream and downstream of the perforated plate to detect the local pressure. The results show that three kinds of flame phenomena were observed: “Pass”, “Quench” and “Near limit”. The “Pass” mode is characterized by successful flame propagation, and involving laminar flame, jet flame, and turbulent flame. Three pressure peaks can be observed on the pressure curve of the sensor in the upstream region. The first peak pressure is equal to two times the initial pressure. The flame tip speed in the downstream region decreases with the increase of the perforated plate length, and two pressure peaks were observed. In the “Quench” model, the flame does not successfully pass through the perforated plate. Furthermore, there are only two pressure peaks on the pressure curve in the upstream region and one in the downstream region. With the increase in the perforated plate length, the critical initial pressure for flame quenching also increases.

Surgical Management of Non-Malignant Esophageal Perforations: A Single-Center Analysis Over a 15-Year Period

Purpose: Esophageal perforations are associated with high morbidity and mortality. Different nonoperative and operative treatment options have been proposed. This study focuses on the impact of different surgical treatments in nonmalignant esophageal perforations and tries to identify predictors of mortality in a single tertiary center over a 15-year period. Methods: From 2002 to 2017, patients with surgically managed esophageal perforation were identified from our database. Patients with esophageal malignancies were excluded. Etiology, clinical data, treatment, and outcome were analyzed. A multivariate logistic regression analysis was performed to investigate the impact on mortality. Results: A total of 72 patients were identified. The majority of perforations were iatrogenic (54.2%) followed by Boerhaave’s syndrome (23.6%). Most ruptures were found in the distal third of the esophagus (59.7%) measuring <3 cm (61.1%). Patients were treated with exploration and drainage (8.3%), primary suture and patch reinforcement (36.1%), resection and restoration of continuity (25.0%), or resection without restoration of continuity (30.6%). Delayed therapy significantly correlated with sepsis (p < 0.0001) and mortality (p = 0.032). A correlation between an increasing perforation length with sepsis (p = 0.012) was observed. A higher Perforation Severity Score (PSS; OR 4.430; 95% CI 1.143–17.174; p = 0.031) and a higher American Society of Anesthesiologists (ASA) score (OR 2.923; 95% CI 1.011–8.448; p = 0.048) were associated with mortality in multivariate analysis. Conclusion: Esophageal perforations are associated with high mortality, and larger ruptures are associated with worse outcome. Rapid diagnosis and treatment are crucial for patient survival. Hence, PSS and ASA score help to identify high-risk patients. The advantage of surgical management lies in the rapid control of the septic focus in an already critically ill patient. Though, the kind of surgical technique needs to be adjusted to the individual situation.

Transient deliverability evaluation for a slanted well in a slab gas reservoir

ABSTRACT The present work provides an algorithm to calculate transient deliverability of a slanted well in a slab gas reservoir. Firstly, transient pressure response of a slanted well has been analyzed and the solutions in Laplace space under three boundary conditions have been derived by point source function and Green function. The solutions in real space can be obtained through the Stehfest inversion by using the superposition principle. Based on the transient pressure analysis, a transient productivity analysis method has been presented in this paper. The influence factors of productivity such as the deviation angle of a slanted well, perforation length, permeability anisotropy ratio, and horizontal permeability to the IPR curve and open-potential rate have been discussed.

Numerical study of near-wellbore hydraulic fracture propagation

Hydraulic fracturing is a major technique used to stimulate shale gas development. In this paper, the fracture propagation path, critical water pressure and deflection angle during the hydraulic fracturing process are analyzed using the maximum tangential strain and incremental crack growth method. After verifying the present numerical method by using published experimental results, this method applied to study the effects of the stress anisotropy coefficient, the perforation length and angle, the water injection pressure and Poisson’s ratio on both the fracture propagation path and the critical water pressure. Furthermore, the effect of T-stress on the crack extension trajectories under different loading conditions is analyzed. The parameter analysis indicates the following: the greater the stress anisotropy coefficient and perforation length, the sooner the fracture reorients to the direction of horizontal stress. A perforation angle that approximately aligns the perforation with the direction of the horizontal stress is recommended to decrease the near-wellbore tortuosity and critical water pressure. The critical water pressure increases with the stress anisotropy coefficient and perforation angle, whereas the perforation length exhibits the opposite trend. The grey relative analysis indicates that the perforation angle is the most important controlling factors in complicating the hydraulic fracture propagation path near-the wellbore. The fracture propagation path is not significantly affected by Poisson’s ratio under high-pressure water injection. In addition, T-stress can significantly affect the fracture propagation path of closed fractures; however, its effect can be ignored for open fractures. The conclusions obtained from this research are important to gain a better understanding of the near-wellbore hydraulic fracture growth process under various conditions.

Acoustic characterization of additive manufactured perforated panel backed by honeycomb structure with circular and non-circular perforations

This paper studies the acoustic properties of an additive manufactured micro-perforated panel backed by a periodic honeycomb structure. Extrusion-based Fused Filament Fabrication (FFF) technique of Additive Manufacturing (AM) is used to fabricate the integrated honeycomb structures with a perforated face sheet. Normal absorption coefficient of the fabricated structure is measured in impedance tube using two microphone transfer function method. A generalized analytical formulation based on unit section analysis applicable to various cross sections of perforations has been proposed to predict the absorption coefficient, where shape dependent viscous effects in the perforation are incorporated by deriving effective complex density of the medium. To study the effect of perforation shape, three geometries viz., circular, triangular and square perforations are considered for analysis where triangular shape found to have more absorption coefficient and lower frequency of peak absorption. In addition, broadband absorption coefficient of proposed structure has been demonstrated by deploying hexagonal cells of different lengths in a unit section. The analytical results are compared with experimental results and a good agreement is observed between them. A parametric study is conducted to understand effect of perforated hole size and cell length on the absorption coefficient and peak frequency. Results show that the proposed structures can be tuned to desired frequency range by altering geometric parameters like cell length, shape and size of perforation hole. Technique and methodology presented in the current study gives an alternative way to design and fabricate honeycomb structures with perforations for acoustic applications such as aircraft cabins, ship structures and building acoustics.

A Theoretical Model for Hydraulic Fracturing through Two Symmetric Radial Perforations Emanating from A Borehole

The production enhancement of oil, gas, or geothermal reservoirs through hydraulic fracturing requires an in-depth study on the fracture initiation and propagation from the borehole. According to the linear elastic fracture mechanics, a theoretical model is developed to calculate the stress intensity factors of two symmetric radial cracks emanating from a pressurized borehole. The maximum tangential stress criterion under the mix-mode condition is developed to investigate the hydraulic fracture initiation. The critical water pressure and critical initiation angle predicted by the theoretical model match closely the experimental results reported in the literature. The influence of the stress anisotropy coefficient, the perforation angle and length, the borehole radius, the ratio between the water pressures in the fracture and the borehole, and Biot’s coefficient are investigated. Moreover, the effects of the injected high water pressure (i.e., larger than the critical water pressure) on the fracture initiation angle are studied to further understand the characteristics of hydraulic fracture initiation. The results indicate that the perforation angle and length, the borehole radius, and the stress anisotropy coefficient have a relatively strong influence on the critical water pressure and critical initiation angle. During high-pressure water injection, the fracture initiation angle decreases as the ratio between the water pressure in the fracture and the borehole and Biot’s ratio increase. The theoretical model provides a comprehensive understanding of the fracture twist, the mixed-mode fracture propagation feature, and the hydraulic fracturing optimization.

Experimental investigation on perforation of shale with ultra-high pressure abrasive water jet: Shape, mechanism and sensitivity

Perforation is critical to create a flow path between a shale reservoir and the production tubing to ultimately achieve supercritical carbon dioxide (SC–CO2) hydro-jet fracturing and natural gas production. However, the mechanisms of ultra-high pressure abrasive water jet (UHP-AWJ) perforation in shale remain unclear. To address this concern, experiments are designed using the Taguchi method to simulate UHP-AWJ perforating in practice. The UHP-AWJ perforation mechanisms are investigated by measuring the reflection angle, the length of perforation, testing strain, and perforation pressure. The results indicate that there are two typical perforation tunnel shapes, depending on jetting flow, back flow, and abrasive action. During UHP-AWJ perforating, the reflection angle decreased from 180° to 40° (by 77.4%), while the length of perforation increased following an exponential trend, and the perforation pressure rose with fluctuations owing to dynamical jetting. In addition, the effects of influential factors, including AWJ pressure, AWJ distance, AWJ time, and casing thickness on the evaluation indexes (such as length of perforation, the maximum diameter of perforation, mass loss of shale, perforating speed, and effective diameter of perforation) are discussed thoroughly. Moreover, the axial pressure is more than twice the radial pressure due to the strong impingement of the water jet. The experimental error of the perforation pressure is only 1.09%, indicating the reliability of our results. Three main stages of UHP-AWJ perforation based on the above results are outlined and summarized.

Perforator Dissection Simulation: A High-Fidelity Five-Flap Porcine Training Model.

Perforator dissection can be technically demanding with a steep learning curve. Inadvertent perforator damage during dissection can be minimized with practice and familiarity with tissue-handling techniques unique to perforator dissection. There currently lacks a simulation model that mimics the human perforator in size and course. We present a porcine training model with five consistent perforator flaps per side that can be readily harvested and is a reproducible simulation model. Five fresh cadaveric pigs were used in this study to evaluate the feasibility and location of the perforators. Ten perforators were dissected out in each pig (five per side) by the same surgeon. The length of perforator was measured and intramuscular route was noted. The ease of dissection was graded, and its similarity to actual surgery was graded as well. Five consistent perforators were identified across each side of five fresh cadaveric pigs. The perforators were located, namely in the neck, anterior flank, posterior flank, rectus and hindlimb. They were fasciocutaneous and had an intramuscular course of each (average 2.5cm length). The perforators were found to be on each side of the pig, giving ten perforators for dissection practice in total. The five perforators named in this porcine model are easily replicated and can be performed for perforator dissection simulation and practice.

Pediatric gastric perforation beyond neonatal period: 8-year experience with 20 patients

To describe the characteristics, treatments, and prognosis of pediatric gastric perforation patients beyond neonatal period. Twenty pediatric patients beyond neonatal period were included in this study. Medical records were reviewed and clinical characteristics were analyzed. According to the outcomes, patients were divided into the survival group and the death group. Death time was documented, and survival patients were followed up. The degree of severity was calculated using pediatric critical illness score (PCIS). Differences between the two groups were analyzed by the Student's t-test, Mann-Whitney test and Chi-square test appropriately. Gastric perforation was diagnosed in 20 pediatric patients beyond neonatal period, including 6 males (30%) and 14 females (70%), with the age of 37.18 (15.90, 107.12) months, and the range was from 4.30 months to 14.17 years old. They had different manifestations, etiologies, sites of perforation and surgery procedures. Among the 20 cases, 14 (70%) survived and 6 (30%) died. Age, gender, length and number of perforation had no statistically difference between the two groups. However, PCIS, ischemia of gastrointestinal wall, and transmural necrosis of gastric wall were statistically different. For the survival group, during a follow-up period of 50 (36, 68) months, ranging from 2 months to 8 years and 7 months, one patient had a second-time perforation, another 3 patients had brain injury symptoms, and the rest 10 patients had good quality of lives. Gastric perforation of pediatric patients beyond neonatal period causes a mortality of 30% on this study. Spontaneous great curvature of gastric wall perforation has the highest morbidity. Low PCIS predicts for unfavorable prognosis. Most of the survival patients have satisfactory living quality after operation.

The effects of some parameters on perforation tip initiation pressures in hydraulic fracturing

Perforations play an important role in hydraulic fracturing as channels of fracturing fluid penetrating into reservoirs. The perforation geometry and the geo-stresses of reservoirs could affect the initiation pressures (i.e. the critical hydraulic pressure as perforation tips start to initiate), and the fracture initiation direction which could affect the fracturing fluid flowing into reservoirs. In this paper, two collinear perforations emanating from a wellbore were considered, and by using conformal mapping techniques, the stress intensity factors (SIFs) of mode I and mode II at the perforation tips were obtained. According to the maximum tangential stress criterion, i.e. MTS criterion, the analytical solutions of the initiation pressures and the initiation angles at perforation tips were obtained. The theoretical results were compared with the previous test results by using cubic concrete models and the previous in-situ measuring results. The prediction results of initiation pressures generally agreed with the test results and the in-situ results. Finally, the effects of perforation lengths, perforation angles with the major principal stress and the principal stress difference on hydraulic fracturing were analyzed. The results showed that the optimal perforation angles should lie in the range from 0° to 30°, and the optimal perforation length should 2 or 3 times the wellbore diameter.

Accuracy of two electronic apex locators in locating root perforations in curved canals in dry and wet conditions: A comparative in vitro study

The aim of the study was to evaluate the accuracy of iPex and Vdw gold apex locators in detecting simulated root perforations in curved canals in the presence of 3% sodium hypochlorite (NaOCl) and 2% chlorhexidine (CHX). In this comparative in vitro study Twenty mandibular molars with curved mesial roots were selected and perforation was made in the danger zone 4 mm from the furcation area. The actual length of the perforation site was measured using stereomicroscope software using a #15 K file, following which the teeth were embedded in alginate molds. The perforation site was electronically measured using two apex locators, iPex and Vdw gold in dry condition and in the presence of 3% NaOCl and 2% CHX. The values obtained were compared using the Friedman and Wilcoxon signed-rank test with level of statistical significance set at P ≤ 0.05. In dry condition, Vdw gold showed near accurate values, i.e., 0.25 mm from the manual value whereas iPex showed a significant difference (P < 0.05) of 0.76 mm from the manual value. In the presence of 3% NaOCl, both the apex locators showed a significant difference (P < 0.05) from the manual value with iPex showing a difference of 0.70 mm and Vdw gold showing a difference of 0.74 mm. The most accurate values were determined by both the apex locators in the presence of 2% CHX with iPex showing a deviation of 0.13 mm and Vdw gold showing a deviation of 0.39 mm from the manual. In dry condition, Vdw group showed better results than iPex in determining the length of the root perforation. In wet condition, in the presence of 2% CHX, both the apex locators accurately measured the perforation site, whereas in the presence of 3% NaOCl, both the apex locators showed a significant difference (P < 0.05) from the manual value in detecting the root perforation.

Geometric influence of perforated plate on premixed hydrogen-air flame propagation

Geometrical influence of the perforated plate on flame propagation in hydrogen-air mixtures with various equivalence ratios and initial pressures was experimentally investigated in a channel with the length of 1 m and the cross-section of 7 cm × 7 cm. The perforated plate has the same cross section and three thicknesses of 40 mm, 80 mm and 120 mm. High-speed schlieren photography was employed to capture the flame shape evolution and derive the flame tip velocity. High-speed piezoelectric pressure transducers were flush-mounted upstream and downstream of the perforated plate to measure the pressure transient. It was found that, with the perforated plate in the path of flame, flame undergoes either “go”, or “quench” propagation mode. The limit between these two was dependent on the geometrical size of the perforated plate and the initial conditions of mixtures. Both velocity and pressure were effectively attenuated with the increase in the perforated plate length. Moreover, for “go” propagation mode, the flame process through the perforated plate was characterized by three obvious stages: laminar flame stage, jet flame stage and turbulent flame stage. Whereas, only laminar flame stage was observed in the “quench” mode.

PS01.086: TRANSGASTRIC VACUUM DRAINAGE FOR OESOPHAGEAL PERFORATIONS: A SIMPLE TECHNIQUE FOR A COMPLEX PROBLEM

Abstract Background We present an updated case series of patients treated with a novel Transgastric (TG) drainage technique, previously published by the senior author in 2008 [Ref], which has now been used in 6 hospitals across United Kingdom and Ireland. The technique establishes vacuum drainage of the lumen of the injured oesophagus whilst maintaining its patency, effectively exteriorizing complex oesophageal perforations to allow healing. Methods Patients presenting with Boerhaave or iatrogenic rupture, undergo an initial decontamination of the chest with drainage as required. A 32–36 Fr Chest drain is inserted in a PEG guided technique, where the proximal end of the drain is positioned 5 cm above the perforation site within the oesophagus, whilst the distal end is pulled out through the stomach and abdominal wall. Continuous low-pressure suction at -10 cm water is applied. Patients continue to drink water. Further intervention is not required until the leak has healed and the drain removed. Results We have used this technique in 20 patients in our institution (3 iatrogenic perforations, 17 Boerhaave), with a median age of 72 (range; 55–85). Perforation length ranged from 1–15 cms. Three cases were performed after stenting failed to control the leak. Pleural decontamination required thoracotomy (n = 12), VATS (n = 2); in 6 cases, no pleural decontamination was required. There were four in-hospital deaths. Median duration from surgery to removal of TG drain was 31 days (range; 10 - 71). Two patients required post discharge dilatation for stricture and are currently asymptomatic. Conclusion TG drainage in effect exteriorizes the oesophageal lumen at the site of oesophageal perforation, encouraging the perforated edges to appose and allow healing by secondary intention. Mediastinal sepsis drains through the transgastric drain (on suction) and intercostal drains placed at decontamination (off suction). Patients tolerate it well, drinking while their perforation heals, avoiding nasogastric intubation. [Ref] Berrisford RG, Krishnadas R, Froeschle P, Wajed S. European Journal of Cardiothoracic Surgery 33(2008):742–744. Disclosure All authors have declared no conflicts of interest.

Mechanism of supercritical carbon dioxide (SC-CO2) hydro-jet fracturing

Supercritical Carbon Dioxide (SC-CO2) hydro-jet fracturing can increase gas production and reduce carbon dioxide emission, and is considered as a promising alternative for shale gas exploration. SC-CO2 hydro-jet fracturing technology has resulted in multi-fracture network in the YanChang Well of Ordos Basin, China. However, the mechanism of SC-CO2 hydro-jet fracturing is still not clear. To address the problem, experiments and specimens were designed based on Orthogonal Experimental Design (OED) to investigate the influential factors, including jet pressure (Pin), jet distance (S), nozzle diameter (dn), perforation length (L) and perforation diameter (dperf). In addition, the evaluation indexes, ambient pressure and the fracture profile were deeply discussed. The investigation results indicated that crack initiation on the root of perforation was prevented by the higher SC-CO2 jet pressure. Particularly, when the nozzle diameter was more than the inlet diameter of casing (3 mm), the crack number on perforation dropped sharply. When the optimal perforation length and perforation diameter were respectively 50 mm and 6 mm, the peak values of the crack number and distribution range were observed. The results of Analysis of Variance (ANOVA) demonstrated that jet pressure and perforation length were the main influential parameters. With the increase in ambient pressure, the threshold pressure of fracture initiation increased. Three patterns of crack extension directions were found in the experimental specimens: surface fracture, longitudinal fracture, and transverse fracture.

A theoretical model for hydraulic fracturing through a single radial perforation emanating from a borehole

This paper considers the problem of the plane-strain fluid-driven fracture propagation of a single radial perforation emanating from a borehole. A maximum tangential strain criterion is proposed to study crack propagation during hydraulic fracturing; this criterion considers the changes in not only the mode-I stress intensity factor caused by the pore pressure but also the mode-II stress intensity factor caused by the anisotropy of the far-field stress. The critical water pressure and the critical initiation angle at the onset of crack propagation are studied using the proposed theoretical method. The effects of the stress anisotropy coefficient, the borehole radius, the perforation length, the ratio of the water pressures inside the fracture to that of the borehole, Biot’s coefficient and Poisson’s ratio on both the critical water pressure and the critical initiation angle are discussed. The parameter analysis indicates that the perforation length, the borehole radius and the stress anisotropy coefficient significantly affect the critical water pressure and the critical initiation angle. The critical water pressure decreases as the ratio of the water pressure inside the fracture to that of the borehole and Biot’s coefficient increase, whereas the critical initiation angle is not affected by these parameters. The critical water pressure increases and the critical initiation angle decreases as the Poisson’s ratio increases. During high-pressure water injection, the fracture initiation angle decreases with increases in the water injection pressure, Biot’s coefficient and the ratio of the water pressure inside the fracture to that of the borehole; however, the angle is not affected by Poisson’s ratio. The theoretical model provides a comprehensive understanding of the characteristics of hydraulic fracturing under complex loading conditions. The results also provide a basis for quantitative investigations of the engineering design of hydraulic fracturing treatments.

Transmuscular Ultrasonography of the Placement of Thoracolumbar Pedicle Screws: A Cadaveric Study

Transpedicular screw fixation has a biomechanical advantage of improving fusion rates. In posterior thoracolumbar immobilization, a large number of screws cause perforation to the pedicle or vertebral body. Radiography and computed tomography (CT) have been used to minimize this complication. The ability of ultrasound (US) to detect the pedicle breach during placement of the screw is unknown. The aim of this study was to evaluate the sensitivity of US for detecting breaches. A B-type transducer was used to scan 216 titanium pins inserted into cadaveric pedicles. Of the pins, 180 were intentionally misplaced: 90 pins breached the lateral wall of the pedicle, and 90 pins pierced the anterior wall of the vertebral body. US images were reviewed by 3 examiners blinded to both the procedure and the corresponding CT findings. The perforation length of pins was measured by 3 radiologists on CT images. CT data were divided into 2 groups. In group 1 (perforation length 0-2 mm), sensitivity of US for detecting lateral wall and anterior wall perforation was 80.95% and 76.42%, respectively; in group 2 (perforation length 2-4 mm), sensitivity was 94.79% and 91.93%. Overall sensitivity of US to detect lateral wall and anterior wall perforation was 89.63% and 86.30%, respectively. The sensitivity of US for detecting perforation was greater in the lateral wall than in the anterior wall. Sensitivity of US was greater in group 2 than group 1 for both lateral and anterior perforation. US can be applied to detect perforation of ≤4 mm. Use of US may improve patient safety.