Measurement While Drilling, 2nd Edition

Chapter 8Downhole Turbine Design and Short Wind Tunnel Testing

As an experienced professional embarking on a career in MWD in 1981, having worked as Research Aerodynamicist at Boeing and Turbomachinery Manager at Pratt & Whitney Aircraft, the jet engine manufacturer, and having earned graduate engineering degrees from Caltech and M.I.T., I had envisioned MWD turbine design as a low-tech “slam dunk” affair. Nothing could have been farther from the truth. In fact, nothing taught in classical aerodynamics applied that could have been reasonably used for downhole tool design. To understand why turbine design is frustrating, one needs only to compare the contrasting operating environments seen by MWD versus jet engine turbines. We will do this in the following section; fortunately, it turns out that good turbine design can be approached systematically using basic physical principles.

8.1 Turbine Design Issues.

A standard MWD turbine is shown in Figure 8.1 where the mud flows from left to right. A single “stage” consists of an upstream “stator,” which does not rotate, and a downstream “rotor” which does. The shaft and alternator combination to which the rotor is connected is not shown. The turbine transforms the kinetic energy of the mud into electrical energy used to power both logging sensors and siren pulser. The demands on the turbine are nontrivial. Up to several horsepower, e.g., 2-3 HP, may be required in a modern high-data-rate tool, which is significant in view of mechanical ...