With the exploration of oil and gas sources moves further to greater depths and into harsher environments,the working condition of pipe string becomes increasingly severe.As the weakest part of the string,the failure of threaded connections occurs frequently.Full-scale experiments are costly,time consuming and complex loads are difficult to apply.Based on three-dimensional elasto-plastic finite element analysis,a numerical platform for threaded connections is developed,which is a powerful complement to physical experiments.The calculated ultimate working torque of threaded connections by the numerical platform is consistent with the data in API standard (without axial tension).Furthermore,the numerical platform can be used to analyze the three-dimensional mechanical properties of threaded connections under complex loads.The numerical platform can evaluate the structural and sealing integrity of threaded connections accurately,and determine the load limits of threaded connections.

The continuous wave pulse generator with rotary valve is an advanced and key equipment in high-rate measurement while drilling (MWD) and logging while drilling (LWD) telemetry systems. It generates an encoded mud pressure wave signal to transmit real-time information from down-hole to surface. For the sake of the transmission distance of the signal and the intensity of the signal, an optimized condition for the generator should be clarified, i.e. maximizing mud-pulse pressure while simultaneously minimizing the power consumed by the rotor. In this study, the CFD method was utilized to analyse the velocity and pressure field inside a four-hole rotary valve under different working conditions, and the effect of four key parameters, the mud flow, the rotational speed of the rotor, the axial gap between stator and rotor and the radial gap between rotor and housing, was studied on the performance of the generator. The results showed that the amplitude of the mud pressure and the power consumed by the rotor increased if the flow rate increased and decreased with the increase of the magnitude of the axial gap and the radial gap. Once the axial gap or the radial gap was reduced, a negative pressure zone raised which is adjacent to the region behind the rotor, thus hindered the flow. When the axial gap was reduced by 50%, the amplitude of the mud pressure and the power consumed by the rotor were raised by 78.8% and 73.2% respectively. Similarly, as the radial gap was reduced by 50%, the amplitude of the mud pressure was increased by 67.1% and the power consumed by the rotor was increased by 107.7%. The rotational speed of the rotor remarkably affected the power consumed by the rotor and the period of the generated signal as well. However, it indicated no significant influence on the amplitude of the mud pressure. The findings are helpful in understanding the mechanism of continuous wave signal generators with rotary valve and the effects of key factors on its dynamic performance.

In drilling application, tool joints are often subjected to complex loads, such as axial tension, bending moment and working torque. With the development of the ultra-deep and extended reach drilling technology, bending moment plays a more and more important role. However, few studies claim to study the effect of bending moment on the tool joints' connection performance. In addition, the influence of the direction of bending moment on tool joints is not published. This paper established a three-dimensional finite element model of the tool joint, and analyzed the mechanical behaviors of the tool joint under make-up torque, axial tension and bending moment with the explicit dynamic finite element method. Compared with a two-dimensional axisymmetric model, the three-dimensional finite element model can effectively simulate the make-up performance of the tool joint by taking the helix angle of the thread into consideration. The results show that the make-up torque can make the force acting on the tool joint unbalanced. Moreover, the stress distribution of the tool joint presents a distinct asymmetric characteristic under the bending moment. Besides, the bending moment direction, which not merely influences the value of moment borne by the contact surfaces between the pin and box, also has a certain effect on the ultimate working torque of the tool joint. Hence, the objective of the work presented in this paper was to explain that the bending moment has an obviously asymmetric characteristic and a strongly influence on the tool joint. In this paper, a method for calculating the ultimate working torque of the tool joint under complex loads is developed. The ultimate working torque diagram of the tool joint is then obtained to define the limits of operation loads.