Measurement While Drilling, 2nd Edition

Chapter 4Transient Constant Area Surface and Downhole Wave Models

Overview

In Chapters 2 and 3, we assumed harmonic or sinusoidal Δp(t) excitations, for the purposes of analysis; these two chapters considered, respectively, comprehensive six-segment waveguides and simpler pipe-alone and collar-pipe models for downhole signal analysis and optimization. The results are directly applicable to “frequency shift keying” (FSK) telemetry. They are also useful in determining the extent to which constructive wave interference methods might be employed in signal enhancement, since destructive signal cancellations associated with random phase-shifting are not present. We focused on a particular downhole “forward” problem in Chapters 2 and 3, that is, the mathematical properties of the total created pressure field when a harmonic Δp is prescribed at a specific source location at a given frequency. The strength of Δp, that is, its dependence on flow rate, valve geometry, rotation rate, mud properties, and so on, is measured separately in flow loops or wind tunnels.

In this chapter, we introduce the study of uphole models. These methods apply at the surface and are principally developed to model reflections of the net upgoing MWD signal at the desurger and mudpump, and to evaluate single and multi-transducer echo cancellation and pump noise removal signal processing methods. Several uphole methods are presented and different models are evaluated and compared computationally against each other. ...