A transient flow analysis method for high-rate mud pulse telemetry in rotary steerable system

With the development of ultra-deep offshore and onshore deep-water wells, there is a growing demand for high-speed data transmission. Mud pulse telemetry (MPT) is the most commercially mature wireless data transmission method. The time-domain parameter analysis of the down-hole mud pulse pressure signal is useful to study the optimization measures of the down-hole signal. Currently, the main approaches are experiment and computa-tional fluid dynamics (CFD) numerical simulations, but both methods are time-consuming and costly, which is not conducive to multi-parameter studies. transient flow modelis widely used to analyze water hammers in pipelines, but its application to mud pulse telemetry (MPT) systems has been less studied. In this paper, based on the classical transient flow equation, the method of characteristics (MOC) is used to solve the governing equa-tion, and the boundary conditions suitable for the MPT are proposed and verified with the experiment and CFD method. Based on the newly established transient flow mathematical model, the generation characteristics of the downhole pressure wave and the influence law of key parameters are studied. The results show that the essence of continuous wave is a three-wave coupling of pressure wave, density wave and flow wave. With the trans-mission of continuous wave, unsteady friction will be generated in the wave region of the wellbore, increasing the attenuation degree of the signal. The amplitude of continuous wave increases with the increase of density and displacement, independent of frequency and viscosity. However, as the frequency and viscosity increase, the continuous wave will decay faster. This paper provides the new transient flow method with fast computational time and a technical means for MPT studies under subsequent drilling conditions.