Highly Flexible Mud-Pulse Telemetry: A New System

Abstract

Abstract Mud Pulse Telemetry (MPT) systems enable the MWD/LWD companies to transmit to surface valuable directional and formation data during the drilling process. This data is used to optimize the drilling process, making drilling operations more cost efficient and allowing the drilling of more complex wells. The major factors limiting MPT data rates include maximum downhole signal strength, signal attenuation, surface induced noise and surface piping induced signal reflections. Most of these are not predictable, not arbitrarily adjustable and potentially change their properties during the course of data transmission. To achieve maximum possible data rates under those challenges, telemetry systems must be highly flexible, both downhole and at the surface receiver. Downhole, the transmission tool should be able to support different signal types and different signal frequencies to optimally use the transmission channel (the mud filled pipe bore).These signaling parameters should be changeable during operation. On surface, sophisticated noise processing should be employed to increase the overall system Signal-to-Noise Ratio (SNR). This paper describes a new system for mud pulse telemetry that supports two signaling types, different signal modulations and various signal frequencies. The new system comprises a novel mud pulser and a digitally controlled, automatically adjusted surface system. With the downhole mud pulser in the borehole, the new system allows the optimization of the mud pulse telemetry process for maximum MWD/LWD information at surface while drilling the well. This paper introduces the system and gives details on how the achieved high speed data rates of the new telemetry system have helped to deliver real time answers while drilling. Introduction Mud Pulse Telemetry (MPT) systems share a common communication principle (Figure 1). Downhole, drilling fluid passes a moving valve that in some fashion restricts flow and in turn generates pressure waves which travel to surface at varying speeds depending on the drilling fluid properties. The mud channel (the pipe bore filled with flowing drilling mud) causes the transmitted signal to be attenuated and further distorted. Depending on the severity of the channel conditions, signal reception can be a difficult task. Major components affecting signal properties include mud pumps, pulsation dampeners, surface piping, pressure transducer locations, drill string components, mud properties, well depth and others. Due to the complexity of the involved parameters and their often varying properties, reliable high speed telemetry requires a system that adapts its downhole and surface settings during drilling. In this paper we discuss a new telemetry system comprising a novel, advanced and reliable mud pulser design and a new surface data acquisition unit with enhanced signal processing capabilities. The system can automatically adjust its decoding parameters during data transmission by making continuous measurements of the transmission channel conditions during drilling. This assures high speed mud pulse telemetry even under highly varying mud channel conditions. The entire system has been extensively tested and improved since 2001 and data rates of up to 20 bits per second (bps) have been achieved in commercial drilling situations. Using this data rate increase of more than 200% compared to previous offset runs, higher quality decision making was attained in various applications. Those optimized, high data rates are essential to support present services and to enable future MWD/LWD services, including reservoir navigation service (RNS), wellbore stability and drilling optimization. In the next sections we introduce the downhole mud pulser and the new surface system with a focus on how to optimize the quality of the signal received at surface. We explain the implemented features and highlight a case that showed higher data rates to be the enabling technology for efficient Reservoir Navigation Service (RNS) operations.