Deep and ultra-deep shale gas resources have great potential, but well drilling faces many challenges. The Polycrystalline Diamond Compact (PDC) bit has become the primary rock-breaking instrument for oil and gas drilling. Reasonable bit structure designs can promote rock-breaking efficiency and extend service life. In this study, reverse modeling technology is used to analyze the structural characteristics of PDC bits collected in the field, and the influence of the structural characteristics of the bit at a specific interval on the rate of penetration (ROP) and drill footage is investigated using the Spearman rank correlation coefficient method. The number of blades, cutting angle of the cutters, crown rotation radius, internal cone angle, and diameter of the cutters are discovered to be the main structural characteristics that affect the ROP and footage of the bits, and the degree of influence varies depending on the formation conditions. The number of blades, crown rotation radius, inner cone angle, and cutting angle of the cutters have a significant impact on the ROP, whereas blade thickness, gauge length, gauge width, nozzle equivalent diameter have a significant impact on the bit footage. In addition, a back propagation (BP) neural network is utilized to build a prediction model of bit footage and ROP over a certain interval based on the structural characteristics of the bit. The goodness of fit of the model is greater than 85%, and its accuracy is high. Based on the usage of the bit, the evaluation and prediction of the bit can provide a reference for the structural design and optimization of the bit in a specific interval, guide the bit selection work, rationally plan the drilling operation, and reduce the drilling cost.

In recent years, digital watermarking technology has become an important technology to protect patient privacy in telemedicine. Because medical information is highly sensitive, the security of medical images is a key problem in telemedicine applications. Aiming at the key color image watermarking scheme and the non key color image watermarking algorithm, two targeted attack schemes are proposed to evaluate their security in telemedicine. The target scheme is based on SVD and QR based color image watermarking algorithm, and their embedding process is the same. The proposed attack takes advantage of the prior knowledge of the watermarking algorithm to make the exact embedding space change. Therefore, these changes will lead to an interruption of the extraction process. The experimental results show that the watermarking scheme based on Watermark Based on the scheme of key key safety. This is because the proposed target attack needs to tamper with the key based watermark image, instead of the key based image, to remove the embedded watermark. Our proposed targeted attack has more effective watermark removal performance than other general attacks such as JPEG compression, Gauss noise, and so on.

To enhance the efficiency of the Stinger Polycrystalline Diamond Compact (PDC) cutter in breaking hard rocks, this study focuses on optimizing the cutter intrusion-cutting rock breaking parameters. A numerical calculation model for the rotational breaking of granite by a Stinger PDC cutter was established. A comprehensive statistical examination was performed to assess the influence of various factors on intrusion ability (IA), tangential force (TF), and mechanical specific energy (MSE). The Taguchi method was used to determine the optimal settings for each factor, while analysis of variance was employed to assess the significance and relative impact of these factors on the target outcomes. In addition, the multi-objective function was optimized using the gray relational analysis method. The primary process parameters obtained for the various performance characteristics are the cone top angle (α), the cone top radius (r), the cutter diameter (d), the cutter back inclination angle (β), and weight on bit (P). The impact ratios of these parameters are 6.20%, 7.66%, 3.93%, 17.20%, and 65.02%, respectively. The optimal geometrical parameters are α = 60°, r = 2 mm, and d = 15 mm, while the optimal working parameters are β = 30° and P = 800 N. In the optimal case, IA and MSE were reduced by 55.335% and 15.809%, respectively, compared to the initial case. Despite a 15.706% increase in TF, the overall GRG increased for all three evaluation criteria, with an overall increase in efficiency of 18.229%. The results of this paper can provide guidance for the design of Stinger cutter PDC drill bits.

High-pressure water jet technology is a clean and efficient technology that is widely employed in deep-water geological exploration, deep-water environmental management, and deep well drilling. Nevertheless, the impact mechanism of high confining pressures (high hydrostatic pressures) on jet characteristics remains unclear in deep water and deep well applications, limiting the application of water jet technology in deep water and wells. This paper investigates the water jet characteristics of a cone-straight nozzle through a combination of theoretical analysis, numerical simulation, and laboratory experiments. It analyzes the variations in the potential core length, nozzle pressure drops, and jet dynamic pressure distribution under different confining pressures. The result indicates that within a low confining pressure range, the cavitation is prone to occur at the nozzle's inflection point, with the most significant cavitation under normal pressure. Under the influence of cavitation, the confining pressure affects the jet flow field distribution, jet structure, and nozzle pressure drop with constant flow rate conditions. As the confining pressure increases, the jet dynamic pressure distribution changes, the potential core length initially decreases, subsequently increases, and then stabilizes, and the nozzle pressure drop initially decreases and then remains constant. The impact of confining pressures on jet characteristics is enhanced with the increase in flow rate. This study provides theoretical guidance for enhancing the application of water jet technology under high confining pressures.

The eccentricity of the annular space has been shown to significantly influence energy loss during fluid flow. To investigate the underlying mechanism, a numerical model for narrow-gap horizontal eccentric annular flow was established based on the k–kl–ω turbulence model. The effects of eccentricity and volumetric flow rate on energy loss were systematically analyzed. Incorporating entropy production theory, a new analytical framework was developed to quantitatively evaluate energy dissipation, and the contributions of time-averaged flow and fluid fluctuations to entropy production were examined. Results indicate that in narrow-gap horizontal eccentric annuli, viscous dissipation is the primary source of entropy production, while isotropic turbulent fluctuations contribute secondarily. The area-integrated entropy production rates exhibit a quadratic relationship with eccentric distance and a power-law relationship with volumetric flow rate. Increasing flow rate synchronously amplifies all types of energy losses but enhances the dominance of isotropic fluctuation losses. Moreover, the effects of the flow rate and eccentricity on energy loss exhibit mutual attenuation. This study elucidates the energy dissipation characteristics of narrow-gap horizontal eccentric annular flow, offering valuable theoretical insights for optimizing flow control in drilling and completion operations.