Mud Siren Torque and Erosion Analysis - Measurement While Drilling Signal Analysis, Optimization and Design - page 177

7
Mud 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 topic.
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 real-time information on pre-invaded formations from deviated,
horizontal, and multilateral wells, Measurement-While-Drilling and Logging-
While-Drilling tools are now routinely used instead.
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