Influence of formation in-situ stress on mechanical heterogeneity of shale through grid nanoindentation

Mechanical heterogeneity is a major characteristic of the organic-rich shale.The relation between mechanical heterogeneity and formation in-situ stress has been seldomly addressed but important to understand hydraulic fracture propagation,wellbore stability,and hydrocarbon flow.In this paper,the grid nanoindentation technique was used to characterize the heterogeneity of the mechanical properties of Longmaxi organic-rich shales from various burial depths and in-situ stress.The measured elastic modulus and hardness of each sample are deconvolved into three phases including soft phase,medium stiff phase and stiff phase according to mineral category.As the burial depth and corresponding in-situ stress increase,the overall elastic modulus and hardness of the sample enhance.Simultaneously,the percentage of soft minerals decreases,and the probability distribution tends to concentrate through 95%confidence interval evaluation which demonstrates weakened heterogeneity.Furthermore,SEM images provide evidence that extended cracking,initiated cracking,crushing and ductile deforming always occur around indentation imprints.This confirms that even under deep buried depth and high in-situ stress,brittle fracture and ductile deformation can exist synchronously.This paper demonstrates the influence of in-situ stress on the heterogeneity of shale micromechanics.

Ischemic or toxic injury: A challenging diagnosis and treatment of drug-induced stenosis of the sigmoid colon

A 48-year-old woman was admitted with 15-mo history of abdominal pain, diarrhea and hematochezia, and 5-mo history of defecation difficulty. She had been successively admitted to nine hospitals, with an initial diagnosis of inflammatory bowel disease with stenotic sigmoid colon. Findings from computed tomography virtual colonoscopy, radiography with meglumine diatrizoate, endoscopic balloon dilatation, metallic stent implantation and later overall colonoscopy, coupled with the newfound knowledge of compound Qingdai pill-taking, led to a subsequent diagnosis of ischemic or toxic bowel disease with sigmoid colon stenosis. The patient was successfully treated by laparoscopic sigmoid colectomy, and postoperative pathological examination revealed ischemic or toxic injury of the sigmoid colon, providing a final diagnosis of druginduced sigmoid colon stenosis. This case highlights that adequate awareness of drug-induced colon stenosis has a decisive role in avoiding misdiagnosis and mistreatment. The diagnostic and therapeutic experiences learnt from this case suggest that endoscopic balloon expansion and colonic metallic stent implantation as bridge treatments were demonstrated as crucial for the differential diagnosis of benign colonic stenosis. Skillful surgical technique and appropriate perioperative management helped to ensure the safety of our patient in subsequent surgery after long-term use of glucocorticoids.

Shaly detritus embedded epoxy-resin coated proppants

Proppant plays a significant role in the hydraulic fracturing process, which can affect the production of oil and gas wells. Due to the high density and low adhesion force, the settling speed of traditional proppants is fast, which will lead to the blockage of a crack channel. In this study, a proppant with double layer structure is fabricated by coating epoxy-resin and shaly detritus on ceramic proppants for the first time,respectively. The epoxy-resin enables the shaly detritus to be coated on the proppant successfully, which can provide a new method for shaly detritus treatment. The adhesive ability of shaly detritus and epoxyresin coated proppants(SEPs) is improved by 10.4% under the load force of 500 n N, which prolongs the time for the fracture to close. At the same time, the suspending ability of SEPs is two times higher than the uncoated proppants. Once the guar gum solution concentration is 0.3 wt%, the settling time of SEPs is36.7% longer than that of the uncoated proppants, which can effectively reduce the settlement of proppants in the crack. In addition, the hydrophobicity of the SEPs is enhanced, which reduces the wateroil ratio of crude oil and increases the liquid conductivity tested by deionized water. In summary, this new proppant is expected to promote the development of unconventional oil and gas resources.

Association between Self-reported Snoring and Prediabetes among Adults Aged 40 Years and Older without Diabetes

Background：Several previous studies have shown that snoring is associated with glucose metabolism and the development of diabetes,but rare study has shown the association between snoring frequency and prediabetes,particularly in China.We hypothesized that individuals who snore might have a higher risk of prediabetes.This study aimed to investigate the association between self-reported snoring and prediabetes in a Chinese population.Methods：A cross-sectional study was performed in three large communities of Beijing from December 2011 to August 2012 by recruiting individuals aged ≥40 years old.All participants were requested to complete a detailed questionnaire and undergo anthropometric measurements.A 75 g oral glucose tolerance test was performed in individuals without diabetes.Blood samples of all participants were collected;blood glucose and blood fat levels were measured.Multivariate logistic regression models were built to assess the association between snoring frequency and prediabetes.Results：A total of 13,592 participants （female：66.56%;mean age：56.8 ＆#177; 7.9 years;mean body mass index：25.5 ± 3.4 kg/m2） were included in the final analysis.Of these,30.9% were diagnosed with prediabetes,while 41.3% and 25.4% had occasional and habitual snoring,respectively.Habitual snoring was associated with an increased risk of prediabetes （odds ratio [OR]：1.3,95% confidence interval [CI]：1.1-1.4,P 〈 0.001）,after adjusting for diabetes and sleep-related confounders in the multivariable models.Habitual snoring was also associated with isolated impaired fasting glucose （IFG;OR：1.3,95% CI：1.0-1.6;P 〈 0.001） and isolated impaired glucose tolerance （IGT;OR：1.3,95% CI：1.2-1.5;P 〈 0.001）,but not IFG ＋ IGT （OR：1.1,95% CI：0.9-1.4;P =0.281）.When stratified by total cholesterol （TC） levels,this association between habitual snoring and prediabetes was observed only in individuals with TC 〈5.6 mmol/L （OR：1.4,95% CI：1.2-1.6;P〈 0.001）.Conclusions：Habitual snoring is associated with prediabetes,but only in individuals with TC 〈5.6 mmol/L.Further prospective studies are needed to confirm this finding.

Estimation of load and resistance factors using the thirdmoment method based on the 3P-Iognormal distribution

Load and resistance factors are generally obtained using the first order reliability method(FORM)in which the design point should be determined and derivative-based iterations used.In this article,the thirdmoment reliability index,based on the three-parameter lognormal(3P-lognormal)distribution,is investigated.A simple method based on the third-moment method for estimating load and resistance factors is then proposed,and a simple formula for the target mean resistance is also presented to avoid iterative computations.Unlike the currently used method,the proposed method can be used to determine load and resistance factors,even when the probability density functions(PDFs)of the basic random variables are not available.Moreover,the proposed method does not require the iterative computation of derivatives or any design points.Thus,the method provides a more convenient and effective way to estimate load and resistance factors in practical engineering applications.Numerical examples are presented to demonstrate the advantages of the proposed third moment method for determining load and resistance factors.

Novel empirical model for predicting residual flexural capacity of corroded steel reinforced concrete beam

In this study,a total of 177 flexural experimental tests of corroded reinforced concrete(CRC)beams were collected from the published literature.The database of flexural capacity of CRC beam was established by using unified and standardized experimental data.Through this database,the effects of various parameters on the flexural capacity of CRC beams were discussed,including beam width,the effective height of beam section,ratio of strength between longitudinal reinforcement and concrete,concrete compressive strength,and longitudinal reinforcement corrosion ratio.The results indicate that the corrosion of longitudinal reinforcement has the greatest effect on the residual flexural capacity of CRC beams,while other parameters have much less effect.In addition,six available empirical models for calculating the residual flexural strength of CRC beams were also collected and compared with each other based on the established database.It indicates that though five of six existing empirical models underestimate the flexural capacity of CRC beams,there is one model overestimating the flexural capacity.Finally,a newly developed empirical model is proposed to provide accurate and effective predictions in a large range of corrosion ratio for safety assessment of flexural failure of CRC beams confirmed by the comparisons.