Improvements in MWD Telemetry: "The Right Data at the Right Time"

Abstract

Abstract The 1991 SPE Forum on MWD concluded that current telemetry data rate via mud pulse was inadequate. This paper addresses this issue. New downhole sensors have been continuously added to MWD Systems and have joined the directional measurements and simple formation evaluation tools commercialized in the seventies. As a result, MWD Systems have been challenged to transmit an increasing amount of data to the surface. Most commercial Systems use the mud column as the transmission channel. MWD telemetry is revisited, analyzing in detail the factors affecting the transmission through the mud. Noise sources and new techniques to minimize interference are described and field examples are presented. The maximum data rate achievable through the mud channel is evaluated, and is compared with current and future needs for real-time use. Data compression techniques are discussed. The impact of data rates on log quality, for a given drilling rate of penetration, is illustrated through field examples at different data rates. New techniques of quality checks on the data which allow quantification of the accuracy of the transmission are described with Statistical test results. Examples of current MWD telemetry Systems covering the range of data rates available today (from 0.5 bits/s to more than 5 bits/s) are presented. The use of microprocessors in the new generation of MWD tools is shown to have impacted dramatically the reliability of the transmission, both in quality and versatility with direct benefits to the end user of the data.