The impact study of variable diameter stabilizer on drilling fluid and cuttings transport.

Through numerical simulation, this study investigates the flow field characteristics of the variable diameter stabilizer in drilling tools under various conditions. It analyzes the influence of different flow rates and speeds on axial velocity and pressure distribution. The results indicate that more significant flow rates correspond to higher average axial velocities across sections, facilitating the transport of drilling fluid and cuttings. Increasing rotational speed leads to greater pressure differences between adjacent sections, consequently elevating the overall pressure drop of the tool, which, to some extent, aids in transporting drilling fluid with cuttings. During rotation, the vortex zone on the backside of the stabilizer creates a hovering and accumulation of cuttings, causing mud agglomeration, thereby affecting tool performance. During structural optimization of the tool, priority should be given to a transitional design of the outlet area in the functional core zone, aiming to alleviate the impact of abrupt structural expansions on cuttings transport.

Study on the mechanism of multidimensional cutting teeth and the influencing factors of rock breaking efficiency.

The innovative cutting mechanism of multi-dimensional teeth presents a groundbreaking approach to drill bit design, particularly optimizing drilling efficiency in challenging geological formations such as interlayers and gravel-rich layers within the Changqing Oilfield. Nevertheless, compared to conventional flat-tooth PDC drill bits, several aspects of the cutting mechanism and design parameters for multi-dimensional teeth require further elucidation. This article employs a linear cutting finite element model to establish cutting models for traditional flat teeth and two distinct types of multi-dimensional teeth, designated as Ridge and Benz. It systematically investigates the influence of varying cutting parameters on the effectiveness of rock-crushing within the multi-dimensional tooth-cutting mechanism. This study conducts laboratory-based single-tooth rock-crushing experiments to validate the numerical simulation results. Furthermore, applying principles derived from soil plastic mechanics contrasts the stress states experienced by rocks during the rock-crushing process between multi-dimensional teeth and conventional flat teeth, shedding light on the rock-crushing mechanism employed by multi-dimensional teeth. This research categorizes PDC cutting teeth on the drill bit into two groups: those near the center and those near the outer shoulder. A linear cutting model for teeth positioned near the outer shoulder is developed to analyze the impacts of different rake angles, side clearance angles, and welding errors on the tooth helix angle and the rock-crushing efficiency of the Benz tooth. This comprehensive study is a valuable reference for tailored drill bit design and holds potential for publication in a prestigious scientific journal.

Firm-level short selling and the local COVID-19 pandemic: Evidence from China.

Short seller trading behavior attracts much attention, especially when negative shocks occur. Recent literature has focused on the impact of the COVID-19 pandemic, an unprecedented shock, but evidence on short sellers' reactions is quite scarce. This paper investigates how short sellers responded to the local COVID-19 pandemic in China. Empirical results show that greater numbers of newly confirmed COVID-19 cases in listed firms' headquarters locations are associated with more subsequent short selling of those firms. The results hold after addressing other potential concerns. In addition, the impact of the local COVID-19 pandemic on short selling is stronger for firms with weaker financial conditions, in more vulnerable industries, and with higher risks of a stock price crash. The impact is alleviated after lifting the lockdown restrictions in Wuhan and becomes insignificant in later outbreaks. Overall, our findings support the informational role of short sellers within the context of the COVID-19 pandemic.

Extreme Temperatures and Firm-Level Stock Returns.

By linking stock returns with weather conditions from 2007 to 2019 in China, we study how firm-level stock returns react to extreme temperatures. Based on a multivariate ordinary least squares regression model with fixed effects, empirical results show that firm-level stock returns decrease with exposure to extreme temperatures. We further explore the heterogeneity in the temperature-return relation to enrich our understanding of the economic mechanism behind it. The impact of extreme temperatures on abnormal stock returns is more pronounced in smaller, younger, more volatile, less profitable firms and firms with more intangible assets. The results indicate that the investor mood likely plays a role in the extreme temperature effect. The impact of extreme temperatures holds after addressing a series of concerns. Overall, our paper provides additional firm-level evidence on the environment-induced mood effect in the stock market.