Search

During the drilling of shale gas wells, the shape of shale cuttings cut by polycrystalline diamond compact bits has an obvious flaky structure. The accumulation of such flaky cuttings is one of the main reasons for high drilling torque and drag and serious back pressure, which affect the drilling speed of the horizontal section of shale gas wells. Therefore, predicting the thickness of the flaky cuttings bed and restraining it are essential for ensuring safe and efficient drilling of the horizontal section of shale gas wells. However, most of the previous research on migration laws for cuttings were based on spherical particles, which affected the accuracy of cuttings bed thickness prediction. In this study, through visualization experiments combined with computational fluid dynamics numerical simulation, the hole cleaning laws of shale gas wells in the long horizontal section were studied, and a set of cuttings bed thickness prediction models and cuttings bed removal process parameter optimization methods were established. Field application was conducted in the Changning 209H24-1 well in the southern Sichuan Basin, China. The results revealed the following: (1) There are significant differences in the migration laws of flaky cuttings and spherical cuttings in the horizontal section. (2) The fitting accuracy of the established long horizontal fragmentation layer distribution model considering multiple factors and the experimental data is as high as 0.973. (3) Based on this model, the drilling parameters of the Changning 209H24-1 well were optimized, which played a good role in wellbore cleaning and ensured the safe and smooth implementation of the later casing operation.

Background & Aims Hepatic venous pressure gradient (HVPG) has a strong predictive value for variceal rebleeding in cirrhotic patients, but the accuracy of an HVPG may be compromised in nonalcoholic steatohepatitis (NASH) cirrhosis. This study aimed to evaluate the accuracy of HVPG and portal pressure gradient (PPG) for predicting rebleeding in NASH cirrhosis after acute variceal bleeding. Patients and Methods Thirty-eight NASH cirrhosis patients and 82 hepatitis B virus (HBV) cirrhosis patients with acute variceal bleeding were included in this study. All patients recived transjugular intrahepatic portalsystemic shunt (TIPS). The prognostic value of HVPG and PPG for variceal rebleeding was evaluated. Results Compared with HBV cirrhosis, NASH cirrhosis demonstrated a lower portal pressure (26.3 ± 6.1 vs. 30.1 ± 4.7; P P = 0.001) , lower HVPG (15.3 ± 3.8 vs. 18.0 ± 4.8; P = 0.003) and lower PPG (18.0 ± 3.7 vs. 20.0 ± 3.4; P = 0.005). HVPG (AUC = 0.82; P = 0.002) and PPG (AUC = 0.72;P = 0.027) had promising prognostic value among NASH cirrhosis patients. The optimal threshold of HVPG and PPG for predicting rebleeding in NASH cirrhosis was 17 mmHg and 20 mmHg. At multivariate analysis, an HVPG ≥17 mmHg was a significant predictor of variceal bleeding (HR 9.40; 95% CI 1.85-47.70; P = 0.007). Conclusions Patients with NASH cirrhosis had lower HVPG and lower PPG than those with HBV cirrhosis. However, the prevalence of rebleeding was similar between two groups. HVPG measurement is still an accurate way to assess the risk of variceal rebleeding in NASH cirrhosis.

With the increase of subway service time, shield tunnels will produce different degrees of damage and destruction. This is related to external factors such as differences in stratum soil, groundwater seepage, construction disturbance to soil, and operating vehicle load. With the increase of subway service time, shield tunnels will produce different degrees of damage and destruction. This is related to external factors such as differences in stratum soil, groundwater seepage, construction disturbance to soil, and operating vehicle load. In order to ensure the operation safety of the subway, long-term and large-scale safety condition monitoring of the shield tunnel is very important. This study summarizes the technical characteristics, layout methods, data collection and processing of distributed optical fiber in shield tunnel deformation monitoring. The feasibility of distributed optical fiber monitoring technology is verified through the segmental deformation monitoring project of Beijing Metro Airport Line and Line 10 shield tunnel. In addition, some experiences in fiber layout and data processing are summarized, which has reference value for similar projects.

Shield tunnels have different degrees of damage due to the differences in the surrounding soil properties, the disturbance of the soil during construction and the repeated loading of vehicles during operation, and there is a tendency to deteriorate with the increase of subway service time. The long-term and large-scale security status monitoring of shield tunnels is an important guarantee for the safety of subway operation. Two diagnostic algorithms based on strain monitoring data are proposed t in this paper, one is for the openness and dislocation of the segments, and the other is for the uneven settlement of the tunnel. The effectiveness of the two algorithms is verified by distributed optical fiber monitoring data of Beijing Metro Line 10. The calculation results are also compared with traditional monitoring methods. The proposition of these two algorithms provides a new idea for the analysis of distributed optical fiber shield tunnel monitoring data, which is beneficial to the promotion of distributed optical fiber monitoring technology.