The Simulation of Fluid Dynamics inside the Continuous Wave Mud Pulser Generator with Four-hole Rotary Valve

摘要

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.