Measurement While Drilling, 2nd Edition

Chapter 7Mud Siren Torque and Erosion Analysis

Three-dimensional flowfields related to the mud sirens used in Measurement-While-Drilling are studied using a comprehensive inviscid fluid-dynamic formulation that models the effects of key geometric design variables on rotor torque. The importance of low torque on high-data-rate telemetry and operational success is discussed. Well known field problems are reviewed and aerodynamically based solutions are explained in detail. Both problems and solutions are then studied numerically and the computer model – developed using flow concepts known from aerospace engineering – is shown to replicate the main physical features observed empirically. In particular, the analysis focuses on geometries that ensure fast “stable-opened” rotary movements in order to support fast data transmissions for modern drilling and logging operations. This chapter, which extends work first presented in Chin (2004), also addresses erosion problems, velocity fields, and streamline patterns in the steady, constant density flow limit. Studies related to drillpipe mud acoustics, signal propagation and telemetry, where transients and fluid compressibility are important, have been presented earlier in this book.

7.1 The Physical Problem.

In drilling longer and deeper wells through unknown, hostile, and high-cost offshore prospects, the demand for real-time directional and formation evaluation information continues to escalate. Because wireline logging cannot provide ...