For improving the hole-enlarging capability, roundness and rock-breaking efficiency of the nozzle in radial jet drilling, a new structure of self-rotating nozzle was put forward. The flow structure and rock-breaking features of the self-rotating nozzle were investigated with sliding mesh model and labortary tests and also compared with the straight and the swirling integrated nozzle and multi-orifice nozzle which have been applied in radial jet drilling. The results show that the self-rotating jet is energy concentrated, has longer effective distance, better hole-enlarging capability and roundness and impacts larger circular area at the bottom of the drilling hole, compared with the other two nozzles. Forward jet flow generated from the nozzle is peak shaped, and the jet velocity attenuates slowly at the outer edge. Due to periodic rotary percussion, the pressure fluctuates periodically on rock surface, improving shear and tensile failures on the rock matrix and thereby enhancing rock-breaking efficiency. The numerical simulation results of the flow structure of the nozzle are consistent with the experiments. This study provides an innovative approach for radial jet drilling technology in the petroleum industry.

Improved Duncan-Chang model for reconstituted hydrate-bearing clayey silt from the South China Sea

The accurate acquisition of downhole engineering parameters, such as real-time pressure and temperature measurements, plays a crucial role in mitigating drilling risks and preventing accidents. In this study, we present the design of a real-time data acquisition and transmission system for drilling operations. The system utilizes a near-bit measurement method to simultaneously measure downhole parameters, including mud pressure and temperature. By analyzing the pressure and temperature frequencies obtained from a quartz crystal pressure gauge and compensating for temperature effects, accurate pressure values are obtained. The resistance value of a PT1000 sensor is measured, and a second-order fitting is performed using laboratory scale coefficients to determine the temperature values. The data acquisition system employs an advanced microcontroller as the main control chip, along with an A/D conversion chip. Additionally, signal amplification, data storage modules, data transmission modules, and relevant peripheral circuits are designed. The field tests were conducted in the 4605~4620 m well section of well Qing 2-76 in the Yumen Oilfield. The results demonstrate stable transmission signals and accurate decoding, enabling the real-time monitoring of pressure and temperature. The tests yielded favorable outcomes, providing a tangible means to analyze the actual operating conditions of the downhole drill string.

The performance of jet pumps depends significantly on their structural and operational parameters. Current research primarily concentrates on theoretical models and laboratory tests, with limited experimental investigations and comprehensive reports concerning jet pump performance under various parameter combinations. In this study, we take a comprehensive approach, integrating both experimental and theoretical methods to assess jet pump performance under optimized process parameters and sand-flushing capabilities. The key findings of this study are as follows: While the characteristic and efficiency equations of jet pumps effectively describe the interaction of critical factors, including the area ratio, pressure ratio, flow rate ratio, and density, they unfortunately do not account for the influence of crucial structural factors, such as the nozzle throat distance, throat length, and diffuser length, on overall performance. Moreover, the parameter optimization technique based on the P-M curve has limitations and requires a tailored design and evaluation to consider the maximum suction capacity in practical engineering contexts. Notably, the nozzle throat distance significantly affects the jet pump suction capacity. Increasing the nozzle throat distance from 6 mm to 12 mm substantially enhances the suction capacity, albeit with a minor reduction in the lifting capacity. Extending the distance from 12 mm to 18 mm initially boosts the suction capacity, followed by a subsequent decline, along with a decrease in the lifting capacity. Interestingly, jet pumps effectively handle sand suction at relatively low pump pressures, creating negative-pressure conditions. As the pump pressure increases, the suction capacity remains relatively stable. However, the lifting capacity increases proportionally with the pump pressure, providing valuable theoretical and technical insights for practical jet pump applications. In summary, our study introduces a comprehensive approach to evaluate jet pumps by integrating experimental and theoretical methods. These insights highlight the intricate relationship between jet pump characteristics and operational parameters, offering essential knowledge for the efficient utilization of jet pumps in various applications.