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Karst fracture-cavity carbonate reservoirs, in which natural cavities are connected by natural fractures to form cavity clusters in many circumstances, have become significant fields of oil and gas exploration and exploitation. Proppant fracturing is considered as the best method for exploiting carbonate reservoirs; however, previous studies primarily focused on the effects of individual types of geological formations, such as natural fractures or cavities, on fracture propagation. In this study, true-triaxial physical simulation experiments were systematically performed under four types of stress difference conditions after the accurate prefabrication of four types of different fracture-cavity distributions in artificial samples. Subsequently, the interaction mechanism between the hydraulic fractures and fracture-cavity structures was systematically analyzed in combination with the stress distribution, cross-sectional morphology of the main propagation path, and three-dimensional visualization of the overall fracture network. It was found that the propagation of hydraulic fractures near the cavity was inhibited by the stress concentration surrounding the cavity. In contrast, a natural fracture with a smaller approach angle (0° and 30°) around the cavity can alleviate the stress concentration and significantly facilitate the connection with the cavity. In addition, the hydraulic fracture crossed the natural fracture at the 45° approach angle and bypassed the cavity under higher stress difference conditions. A new stimulation effectiveness evaluation index was established based on the stimulated reservoir area (SRA), tortuosity of the hydraulic fractures (T), and connectivity index (CI) of the cavities. These findings provide new insights into the fracturing design of carbonate reservoirs.

The current paradigm of joint detection and tracking still requires a large amount of instance-level trajectory annotation, which incurs high annotation costs. Moreover, treating embedding training as a classification problem would lead to difficulties in model fitting. In this paper, we propose a new self-supervised multi-object tracking based on the real-time joint detection and embedding (JDE) framework, which we termed as self-supervised multi-object tracking (SS-MOT). In SS-MOT, the short-term temporal correlations between objects within and across adjacent video frames are both considered as self-supervised constraints, where the distances between different objects are enlarged while the distances between same object of adjacent frames are brought closer. In addition, short trajectories are formed by matching pairs of adjacent frames using a matching algorithm, and these matched pairs are treated as positive samples. The distances between positive samples are then minimized for futher the feature representation of the same object. Therefore, our method can be trained on videos without instance-level annotations. We apply our approach to state-of-the-art JDE models, such as FairMOT, Cstrack, and SiamMOT, and achieve comparable results to these supevised methods on the widely used MOT17 and MOT20 challenges.

The high temperature and high in-situ stress geological environment can significantly affect the mechanical properties, failure modes, and deformation characteristics of deep shale reservoirs. In this study, real-time high temperature triaxial compressive tests simulating the deep shale formation environment (temperature: 25–150 °C, confining pressure: 0–100 MPa) are carried out. The GSI-strength degradation and constitutive models are derived based on the Hoek–Brown criterion. The results show that in low confining pressure conditions, the mechanical behavior of shale is greatly influenced by temperature. Compared with shale at 25 °C, the compressive strength of shale at 150 °C decreases by up to 13.7%, and the elastic modulus decreases by up to 36.9%. The peak strain was increased by a factor of up to 1.4, and the yield stress level was advanced by as much as 7.4%. However, in high confining pressure conditions, the shale plasticity characteristics are significantly enhanced and the failure mode is relatively single. The GSI-strength degradation model can well characterize the variation law of shale strength with confining pressure under high temperature conditions. The statistical damage constitutive model matches the actual stress–strain curve very well, and it can fully reflect the deformation and failure characteristics of deep shale. The findings of this study can help us better understand the variation of mechanical properties of deep shale.

Cement sheath is an annular structure situated between casing and formation, which is designed to seal the formation and reinforce the borehole. However, owing to the surface irregularity and drilling mud residue, the interface between the cement sheath and the formation is one of the weakest parts for fluid leakage causing well integrity issues, which would also affect the reliability of the cement bond logs. To evaluate the cementation state and tensile properties of the cement-formation interface, rock-cement composite disc specimens are prepared, considering key factors such as lithology, interface irregularity, treatment of oil-based drilling mud contamination, and flushing fluid washing. Flushing efficiency of the drilling mud contaminated rock surface, interface cementation characteristic, referenced tensile strength, and tensile fracture morphology are acquired and analysed comparatively. Results show that (1) the flushing efficiencies of shale and sandstone are 74.1 ~ 61.9% and 52.4 ~ 28.4%, respectively, decreasing with the increase in surface irregularity. (2) The rock-cement interface gradually becomes poorly cemented as the surface cleanliness decreasing and the irregularity increasing. (3) Under the condition of drilling fluid contamination, there exists a transitional area at the cemented interface, where microcracks and pores are developed. (4) With the influence of drilling mud contamination, the referenced tensile strengths of shale-cement and sandstone-cement interfaces drop from 2.716 to 0.586 MPa and from 2.840 to 0.007 MPa, respectively. The effects of underground temperature and pressure environment are not particularly considered in this study and would be investigated systematically in future research.

This paper describes early-stage modeling of a thin-film piezoelectric microelectromechanical system (MEMS) scanning mirror capable of random-access scanning over significant range-of-motion. Due to low transduction forces, MEMS mirror technology typically relies on purely resonant operation about a neutral position, or low-bandwidth quasi-static positioning or trajectory following. High energy density of piezoelectric materials can support both high resonant frequencies and large static offsets, allowing scans to be directed in a random-access fashion to specified locations in a large field-of-view. However, this requires coordination of multiple inputs and elastic vibration modes. Here, we identify the linearized modal model for a sample piezoelectric scanner and a simple, open-loop strategy for transitions between full-field scanning and narrow-field scanning in specified regions. Influence of step-wise transition between operating modes on settling time and overshoot is characterized in simulation.

Marine and lacustrine shales are two major important types of organic-rich shales that are usually deposited in the stable ocean basin and deep lake/swamp settings, respectively. In the past decade, commercial development of marine shale gas resources has been achieved. The underdeveloped lacustrine shale also showed great oil and gas potential. Is it feasible to simply copy the development mode of marine shale gas to lacustrine shale? This is what this paper would attempt to answer from the viewpoint of rock mechanics. Using borehole cores from two typical marine and lacustrine shale gas wells, a series of experiments, including X-ray diffraction (XRD), triaxial compression, fracture surface three-dimensional (3D) scanning, and scanning electron microscopy (SEM), were implemented to comprehensively reveal the mechanical difference between marine and lacustrine shales. Postfailure fracture complexity and surface roughness were quantified by fractal dimension and morphology reconstruction, respectively. A new index BInew, considering the influences of the complete stress–strain curve and fracture characteristics, was proposed to evaluate the brittleness of these two types of shales. Results showed that the mechanical properties of marine and lacustrine shales were quite different and should be exploited by following their own characteristics. Mechanical parameters of lacustrine shale, such as compressive strength, Young’s modulus, cohesive strength, and internal friction angle, were much lower than those of marine shale. Different from the typical shear plus bedding splitting failure mode of marine shale, lacustrine shale usually formed only one smooth shear fracture. Based on the newly proposed index, the brittleness of lacustrine shale was significantly lower than that of marine shale. Huge discrepancy in quartz and clay mineral contents and the consequent petrophysical structure divergence were the reasons for the marked mechanical difference between marine and lacustrine shales. Differentiation strategies and effects of hydraulic fracturing for these two kinds of formations were also discussed.

We report the largest and most diverse genetic study of type 1 diabetes (T1D) to date (61,427 participants), yielding 78 genome-wide-significant (P< 5 × 10−8) regions, including 36 that are new. We define credible sets of T1D-associated variants and show that they are enriched in immune-cell accessible chromatin, particularly CD4+effector T cells. Using chromatin-accessibility profiling of CD4+T cells from 115 individuals, we map chromatin-accessibility quantitative trait loci and identify five regions where T1D risk variants co-localize with chromatin-accessibility quantitative trait loci. We highlight rs72928038 in BACH2as a candidate causal T1D variant leading to decreased enhancer accessibility and BACH2expression in T cells. Finally, we prioritize potential drug targets by integrating genetic evidence, functional genomic maps and immune protein–protein interactions, identifying 12 genes implicated in T1D that have been targeted in clinical trials for autoimmune diseases. These findings provide an expanded genomic landscape for T1D.

Study Design Retrospective cohort study.Objectives Patients with IBD are at an increased risk for postoperative complications following surgery. The goal of this study is to investigate if inflammatory bowel disease (IBD) is a risk factor for complications following lumbar discectomy.Methods We identified IBD patients who underwent lumbar discectomy for lumbar disc herniation (LDH) and matched to them with controls without IBD in a1:5 ratio. We excluded patients with a history of spinal injury, cancer, infection, trauma, or surgery to remove the digestive tract. We used multivariate logistic regression analyses to compare postoperative outcomes, including 90-day complications, 90-day emergency department visits, and 90-day readmissions. In addition, 2-year re-discectomy rates and a 3-year lumbar fusion rate were compared between the cohorts.Results After applying the study criteria, we identified 6134 IBD patients with LDH for further analysis. With the exception of dura tears, patients with IBD had significantly higher rates of medical complications, incision-related complications, ED visits, and readmission rates compared to patients without IBD, especially for the 2-year and 3-year rates of disc recurrence and revision surgery.Conclusions Patients with IBD who underwent lumbar discectomy are at a significantly higher rate of complications. Therefore, spine surgeons and other health care providers should be aware of this higher risk associated with IBD patients and properly treat the patients’ IBD before surgery to lower these risks.

In large-scale multi-section hydraulic fracturing, the stress environment of wellbore is extreme complex, often causing the unbalanced stress distribution around the wellbore. That poses great challenges to the integrity of the sheath. In this paper, firstly, triaxial compression test and triaxial cyclic test are carried out at 130 °C to study the deformation characteristics of the cement under high temperature. Then based on that, an appropriate plastic mechanics model is established. Finally, the shakedown theory is applied to analyze the model and acquires a maximum cyclic loading under asymmetric stress. The result shows that (1) the well cement, with the increase of load, shows the plastic flow characteristics and can be regarded as an ideal elastic–plastic material under high temperature. (2) During the cyclic loading and unloading process, the "hysteresis loop" becomes denser, which indicates that the accumulation rate of plastic deformation is continuously declining. The main plastic strain appears in the phase of the first loading. (3) The external pressure Pzplays a positive role in the deformation control of the sheath. With the growth of Pz, the maximum cyclic loading Pmaxwill also increase. (4) Asymmetric stress distribution can significantly affect the bearing capacity of the sheath. If stress difference coefficient λ= 0.3,the Pmaxtends to decrease nearly by 50%. With the growth of λ,the negative influence of stress asymmetry reduces gradually. High external pressure is beneficial to reduce the negative impact of the asymmetry. With the growth of λ,the benefit tends to enhance. (5) In engineering practice, if the geology around wellhole showcases the strong asymmetry (the value of λ is large), some steps need to be adopted to reduce the stress concentration.

Carbonate-rich shale is a newly discovered, promising shale gas reservoir. But field stimulation practice showed that the effect of conventional acid fracturing was very limited. This is what we try to clarify through a comprehensive study. Using downhole cores from a carbonate-rich shale well, mineral quantitative evaluation, acid immersion, and acid corrosion experiments were conducted. Results showed that (1) The surface calcite of carbonate-rich shale was the first to be dissolved by acid; however, acid was blocked by quartz and unable to react with the internal carbonate minerals. (2) High strength was observed in carbonate-rich shale; however, acid immersion slightly weakened the peak deviatoric stress, Young's modulus, and Poisson's ratio by 2.22%, 13.39%, and 2.19%, respectively. (3) Only one acid-induced fracture was connected to the main shear crack under confining pressure, indicating a limited increase in the stimulated volume of this reservoir by acid fracturing. (4) In the carbonate-rich shale, where there was sufficient contact with the acid, the acid exerted a positive effect on fracture propagation; as the acid was consumed, the internal fracture changed insignificantly. The above evidence would explain the ineffectiveness of acid fracturing in carbonate-rich shale reservoirs. The stimulation suggestion discussed may bring about better stimulated volumes for carbonate-rich reservoirs.

Abstract: Rocks in many high-temperature underground engineering applications experience complex stress disturbances, which greatly affect their performance. However, the influence of combining the temperature and fatigue loading on the deformation characteristics of granite has rarely been investigated. In this study, multi-level multi cyclic loading tests were carried out on granite samples over the temperature range of 25–600 °C, revealing the influence of temperature, stress level and number of cycles on the deformation characteristics and energy conversion characteristics. The results show that the deformation behavior of granite under fatigue loading at high temperature is different from that at room temperature. It can be divided into three stages, hardening stage (Stage I), transition stage (Stage II) and softening stage (Stage III), which may be applicable to evaluate the deformation of deep rocks under complex geological conditions. A linear energy storage law that is independent of temperature and loading history was observed. A new calculation method for elastic energy at the peak stress was introduced to modify the traditional method based on the assumption of equivalent elastic modulus at the loading and unloading stage, which can provide a more reasonable and reliable estimate of rock brittleness. The experimental results of this study have important theoretical significance and engineering value for long-term stability evaluation and disaster prediction. Article Highlights:

Influence of temperature and damage-controlled cyclic loading on the deformation of rocks are experimentally studied.

A conceptual model of rock deformation is proposed, which may be more suitable for the evaluation of rock deformation under complex geological conditions.

A new method for accurately calculating the pre-peak brittleness index is introduced, which can provide a more reliable estimate of rock brittleness.