Transmission Characteristics of DPSK Mud Pressure Signals in a Straight Well

摘要

Transmission characteristics of differential phase shift keying (DPSK) pressure signals transmitted in a downhole mud channel are researched by theoretical and numerical methods. With the control logic analysis of a rotating valve in continuous-wave telemetry, a DPSK pressure signal mathematical model is built in accordance with principles of communications and mathematical analysis. In the condition of water-based drilling fluids, drill pipes of a straight well are divided into a number of sections in accordance with wellbore pressure distribution. By transfer function analysis of all the sections, a numerical expression of the signal along the entire length of the vertical drill pipes is obtained and the influence of transmission distance, internal diameter of drill pipes, carrier frequency, drilling fluids viscosity, and air voids on the signal amplitude are analyzed. Numerical calculation shows that the influence of drilling fluids viscosity and air voids on the DPSK signal are the most notable for the signal transmission.