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Based on the leakage of the coalbed methane (CBM) drilling engineering practice of Luan mining area in China, the author determines the safe drilling fluid density range for the stable borehole wall based on borehole wall collapse and fracture pressure. Such parameters as the drilling fluid hydraulic parameters (including pump pressure, pump power and displacement, nozzle diameter, bit pressure drop, bit hydraulic horsepower, circulation pressure drop, impact force and jet velocity) and drilling parameters (including weight-on-bit, drilling rotary speed, bit tooth wear) in each borehole section are optimized. Taking the lowest drilling cost as the controlling target, the drilling parameter optimization model is designed and solved by the genetic algorithm. Furthermore, a software named "CBM borehole wall stability parameter design and optimization" characterized by visualization and applicable for drilling formation condition, which can be used to design and optimize the borehole drilling technological parameters, is developed. This program includes such modules as drilling fluid density prediction, drilling technology design, database management, user management and help. The developed software is proven to solve the drilling leakage effectively in the No.67 borehole practice, which can help drilling engineers to optimize CBM drilling technological parameters safely and quickly.

Defect inspection of small-diameter thin-walled pipes is a difficult problem in the field of nondestructive testing. In this paper, a new detection method based on laser ultrasonics and guided circumferential wave technology is proposed and used to inspect the defects in pipes. First, a theoretical model based on the theory of acoustic propagation in solids is proposed for the small-diameter thin-walled pipes. The dispersion characteristics of the guided circumferential waves of thin-walled pipes are obtained by numerical simulation. Second, a laser ultrasonic system is constructed and used to detect the flaws in the small-diameter thin-walled pipes. Finally, the laser ultrasonic system is used to analyze the welding quality of stainless steel pipes with a diameter of 4.20 mm and a wall thickness of 0.30 mm. The experimental results are in agreement with the theoretical analysis, which demonstrates the reliability and practicability of the laser ultrasonic method in the weld quality inspection of small-diameter thin-walled pipes.

Landfill leachate and domestic sewage decompose and react with the silty clay liner when there is seepage of waste. Municipal waste contaminants have important impacts on the leachate and chemical reaction, and therefore, the interactive effect of municipal waste seepage and chemical reaction on the changes in the properties of silty clay. In this study, acetic acid (CH 3 COOH) and calcium carbonate (Ca-CO 3 ) are used as the seepage fluids to examine the chemical interaction between the leachate and the changes in silty clay and provide a better understanding of the changes due to the interactive effect of municipal waste seepage and chemical reaction on the changes in the properties of silty clay as well as the interactive process. The results show that the interactive process of municipal waste seepage and chemical reaction can be primarily examined as three stages: seepage, mixing of the leachate and silty clay, and chemical contamination. Among the many factors, the type of seepage medium has the most impact on the silty clay properties in terms of the interactive effect between municipal waste seepage and chemical reaction. KeywordsMunicipal waste contaminated silty clay • Interactive effect of seepage and chemical reaction • Silty clay • Seepage • Leachate Editorial responsibility: Agnieszka Galuszka.