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The purpose of this study was to analyze if celiac disease (CD) is associated with increased postoperative complications following single-level posterior lumbar fusion (PLF). A retrospective database review was performed using the PearlDiver dataset. The study population included all patients older than 18 years who underwent elective PLF with diagnosis of CD using International Classification of Diseases (ICD) and Current Procedural Terminology (CPT) codes. Study patients were compared with controls for 90-day medical complications and 2-year surgical complications including 5-year reoperation rates. A multivariate logistic regression was used to determine the independent effect of CD on the postoperative outcomes. A total of 909 patients with CD and 4483 patients in the matched control group who underwent primary single-level PLF were included in this study. CD patients had a significantly increased risk of 90-day emergency department (ED) visit (OR 1.28; P = 0.020). CD patients also demonstrated higher rates of 2-year pseudarthrosis and instrument failure, but they were statistically comparable (P > 0.05). There was no difference in 5-year reoperation rate. There were also no significant differences in 90-day medical complication rate and 2-year surgical complication rate between the two groups. In addition, there were no differences in procedure cost and 90-day cost. For CD patients undergoing PLF, the current study demonstrated increased rate of 90-day ED visit. Our findings may be useful for patient counseling and surgical planning for those with this condition. [ABSTRACT FROM AUTHOR]

With the increasing demand for energy from deep oil and gas reservoirs, oil-well cement slurries are subjected to complex compressive cyclic loading in high-temperature and high-pressure (HTHP) environments. Currently, no standard to guide the evaluation of the fatigue performance of cement slurries under cyclic loading or a systematic investigation to help understand it exists. To fill this gap, this study used a set of innovative HTHP curing and testing devices to mimic the actual operating conditions of deep wells. Cement slurries were cast, cured, and subjected to quasi-static and cyclic loading tests at four downhole temperatures (25, 90, 115, and 140 °C). In the cyclic-loading tests, three loading levels (30%, 50%, and 70%) under 20 MPa confining pressure were applied to study the fatigue performance, and nuclear magnetic resonance (NMR) was employed to identify internal microcrack damage. When the downhole temperature increased from 25 to 140 °C and the cyclic loading level increased from 30% to 70%, the accumulated plastic strain of samples increased by 13.8 times. A large increase in the plastic strain of oil-well cement slurries can significantly reduce the fatigue resistance and service life of oil and gas wells. Based on this research, the authors propose the addition of compressive cyclic loading tests (particularly under HTHP testing conditions) to the current oil-well cement slurry testing standards, which will be very significant for the fatigue performance evaluation of cement slurries used in HTHP environments in deep wells. • Fatigue performance of cement slurries in HTHPs was evaluated for the first time. • Different loading levels were employed to simulate cyclic operating conditions. • High loading level and HTHP increased the accumulated plastic strain by 13.8 times. • Fatigue properties under cyclic loading must be evaluated in deep-well application. [ABSTRACT FROM AUTHOR]

The American Petroleum Institute testing standard (API TR 10TR7) recommends determining the mechanical performance of oil-well cement slurries in an ambient-temperature testing environment. However, with exploration and exploitation resources moving toward deep formations, cement slurries for oil, gas, and geothermal wells are increasingly being utilized in high-temperature and high-pressure (HTHP) in-site formations. It is unknown if the current standard is suitable for assessing the mechanical performance of cement slurry under in-site HTHP conditions in deep wells. To fill this research gap, an innovative experimental platform was developed for this study to mimic the in-site HTHP environments in real production wells; then oil-well cement slurries were cast, cured, and tested at elevated temperatures (i.e., 90 °C, 115 °C, 140 °C) and the confining-pressure (i.e., 20 MPa). The mechanical performance of cement slurries was evaluated under triaxial compression and cyclic loads. The microstructures of cement slurries were also studied. This study revealed that the high-temperature testing environment accelerated the crack propagation and stress drop of stress-strain curves, decreased the failure stress (up to 14.0 %), Young's modulus (up to 16.4 %), and Poisson's ratio (up to 31.7 %), and resulted in more brittle characteristics of cement slurry samples. This study confirmed that using the current standard will significantly overestimate the mechanical properties of oil-well cement slurries in HTHP environments. The authors suggest updating the standard to take HTHP environments into consideration, which should ultimately meet the increasing demands of developing deep oil, gas, or geothermal wells. [ABSTRACT FROM AUTHOR]

Continental shale is abundant with unconventional oil and gas and has considerable potential for exploitation. However, due to differences in the deposition environment, continental shale presents unique characteristics in terms of mineralogy and mechanical properties compared to marine shale. Furthermore, the mechanical influence of fracturing fluid immersion must be considered because of the dual effects on the productive shale system caused by fracturing fluids remaining in the formation. In this study, tri-axial compression tests were performed on Jurassic continental shale specimens collected from an exploratory well (2778–2816 m deep) in the Sichuan Basin of China before and after exposure to fracturing fluids. Meanwhile, two quantitative indicators, the roughness R , which characterizes the widely distributed yield deformation, and the complexity F , which evaluates the complex multi-fractures, were used to distinguish the different brittle-plastic characteristics of specimens before and after fracturing fluid immersion. The results showed that the immersion of fracturing fluids weakened the mechanical properties of continental shale. Two types of fracturing fluid immersion effects were distinguished by the statistics of the failure characteristics of the different layers: lubrication-dominated and softening-dominated. Unlike conventional smooth tri-axial stress-strain curves, many of the post-peak curves were in a 'step-like' shape, corresponding to two sources: one part came from the formation of multi-fractures (brittle characteristics), and the other part came from the softening deformation of main failure surface (plastic characteristics). A new brittleness index, BI new , was proposed considering failure characteristics with different brittleness effects, which could effectively distinguish the brittleness difference before and after exposure to fracturing fluids. • Mechanical variations of continental shale along longitudinal profile were studied. • Different effects of fracturing fluids were distinguished by failure characteristic. • Different sources of additional energy dissipation were recognized. • New brittleness index was proposed incorporating different failure characteristics. [ABSTRACT FROM AUTHOR]

• The unique mineral composition and distribution of carbonate-rich shale were revealed. • Full-scale pore structure and fractal features were characterized. • The comprehensive mechanical properties of carbonate-rich shale were analyzed. • The inner link between micro-structural and macro-mechanical properties was established. • Development strategies for carbonate-rich reservoirs were discussed. As a new growth point of shale gas production, carbonate-rich shale has recently attracted great interest. However, gas production from this reservoir was poor since the properties of the carbonate-rich shale have not been systematically studied. This is an urgent need to be addressed. Downhole cores collected from an exploration well were analyzed by micro-structure experiments (X-ray diffraction, mineral quantitative evaluation, low-pressure nitrogen adsorption, and mercury intrusion piezometry test) and macro-mechanical tests (triaxial compression, Brazilian splitting, and fracture toughness test) to obtain multiscale characterization of carbonate-rich shale. The intrinsic relationship between the microstructural and mechanical characteristics of this reservoir has been revealed. The results showed that (1) The content of carbonate minerals exceeds 30%, just slightly lower than that of quartz. Calcite has large particle sizes and is closely cemented with quartz to form a dense rock skeleton. (2) The maximum adsorption volume, specific surface area, total pore volume and average pore diameter values are poor, which is unfavorable for shale gas accumulation. Limited porosity and permeability and great tortuosity can be obstacles to the release of accumulated gas. (3) High peak deviatoric stress, Young's modulus, and Poisson's ratio were contributed by dense rock skeleton. (4) Narrow maximum main fracture width is not favorable to place proppants and further to create effective gas transport channels. (5) High tensile strength and fracture toughness enhance high breakdown and extension pressure. These comprehensive insights are of great significance for both the exploration and development of carbonate-rich shale reservoirs. [ABSTRACT FROM AUTHOR]

The safe and efficient development of ultra-deep shale gas deeper than 4500 m is closely related to the comprehensive evaluation of the mechanical behavior, brittleness and anisotropy characteristics of reservoir rocks under in-situ stress conditions. However, the above-mentioned information about ultra-deep shale is rarely reported. This study aims to fill this gap by systematically investigating the mechanical and anisotropic characteristics of cores, with 0° and 90° bedding orientations, from different layers in the vertical depth of 4900–4930 m, under confining pressure of 110 MPa. Furthermore, a new brittleness index with three parts related to brittle failure, i.e., the energy storage performance in the pre-peak stage, the performance of elastic energy used to maintain the post-peak failure, and the severity of the energy released during the post-peak stage, all of which are physically meaningful, was proposed. Subsequently, the index was validated and applied to the brittleness evaluation of ultra-deep reservoir rocks. The brittleness was evaluated in the following descending order: black shale of Longmaxi Formation ＞ gray-black shale of Wufeng Formation ＞ limestone of Baota Formation. Overall, the Wufeng- Longmaxi Formation shale still exhibits brittle failure under such high confining pressure, while the Baota Formation limestone exhibits quasi-ductile failure, which is consistent with the phenomenological behavior of cores. Further, various experimental techniques have been employed to study the brittle and quasi-ductile failure mechanisms of reservoir rocks. The anisotropy evaluation results show that the anisotropy degree of the mechanical and brittleness parameters corresponding to the deep formation is significantly lower than that of the shallow formation. The anisotropy degree of strength and deformation parameters (Young's modulus, Poisson's ratio) is closely related to the content of quartz and clay minerals, respectively. The above results are expected to provide data support and theoretical guidance for the development of deep and ultra-deep shale gas in the southern Sichuan region of China. • The mechanical characteristics of ultra-deep reservoir rocks in the vertical depth range of 4900–4933 m are reported. • The influence of the bedding effect on the mechanical behavior of reservoir rocks under high confining pressures is studied. • A new three-part brittleness index in which each part has a clear physical meaning related to brittle failure is proposed. • The brittle and quasi-ductile failure mechanisms of reservoir rocks under high confining pressures are revealed. [ABSTRACT FROM AUTHOR]

The success of commercial exploitation of shale gas has already been achieved in middle-shallow layers of China. But more than 65% of shale gas resources is buried in deep formation (vertical depth ≥ 3500 m), which has not been effectively developed yet. Deep buried depth is the source of a series of challenges. To clarify the influence of buried depth on mechanical characteristics of shale, tri-axial compression tests considering high confining pressures (80 MPa) are conducted with core samples collected from the gas bearing section of a deep marine shale gas well. The results show that the peak deviatoric stress significantly increases with the growth of confining pressure and exhibits an obvious declining trend from bottom to top in longitudinal profile, whereas Young's modulus and Poisson's ratio were all relatively insensitive to buried depth. Unlike conventional smooth tri-axial test curves, many of the post-peak curves are in "step-like" shape, and their corresponding failure patterns are always multi-fractures, all of which are originated from the activation of bedding planes or natural fractures during yielding process and are indications of high brittleness. However, the proportion of specimens with these features decreases from 66.7% to 22.2%, with the confining pressure increased from 30 MPa to 80 MPa. As most of existed indices could not properly describe the brittle characteristic of this type of deep marine shale, a new brittleness index (BI) is proposed by quantifying the complexity of "step-like" post-peak curves in fractal dimension. It is demonstrated that BI could effectively capture the influence of confining pressure on brittleness and distinguish those more brittle layers. Owing to the great reduction of brittleness and fracture complexity under high confining pressure, the fracking network in deep formation might be sparser than that in middle-shallow layer at field scale, leading to the poor performance of past fracking deep wells. • Mechanical properties of deep gas shale covering the entire gas-bearing section are presented. • Step-like shape of post-peak stress-strain curves is spotted and linked with multi-fractures failure pattern. • Dominant failure pattern transforms from multi-fractures to single shear rupture with increasing confining pressure. • Fractal dimension is introduced to establish a new brittleness index to evaluate this type of shale. [ABSTRACT FROM AUTHOR]

A facile sol-gel method is used to fabricate anatase TiO 2 /amorphous carbon (a-TiO 2 /C) and pure a-TiO 2 nanoparticles as anode materials in lithium-ion battery. In the a-TiO 2 /C hybrid, a-TiO 2 is generated along with synthesis of amorphous carbon. Thus, a-TiO 2 is uniformly embedded into amorphous carbon matrix, which showing a flake structure. The flakes are composed of a number of irregularly sized a-TiO 2 /C nanoparticles. Moreover, the flakes have porous channels. This designed structure suppresses the growth of a-TiO 2 nanoparticles and accelerates the diffusion of lithium ions. Therefore, the hybrid materials exhibit an excellent rate and stability performance compared to pure a-TiO 2 in electrochemical testing. The a-TiO 2 /C anode has discharge capacities of 293 mAh g−1 at 0.05 A g−1 and 172.6 mAh g−1 at 0.5 A g−1. Additionally, the a-TiO 2 /C anode retains a long cycling performance of 224.4 mAh g−1 at 0.2 A g−1 over 400 cycles with a capacity retention rate of 86.9%. An average capacity fading loss is 0.03275% per cycle, which is lower than 0.1335% of a-TiO 2 anode per cycle (initial discharge capacity is 290.5 mAh g−1 and final discharge capacity is 135.4 mAh g−1). The results reveal that compounding of amorphous carbon effectively improves the electrochemical performance of a-TiO 2. • The a-TiO 2 /amorphous carbon porous flakes based nanoparticles are produced by a facile process. • Ethylene glycol is both carbon source and solvent without any additional carbon source. • a-TiO 2 is uniformly embeds into carbon matrix. • An average capacity decay is 0.03275% per cycle at 0.2 A/g after 400 cycles. [ABSTRACT FROM AUTHOR]