This paper was prepared for the IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition held in Jakarta, Indonesia, 25-27 August 2008, but was not presented. The author(s) have submitted this paper for inclusion in the SPE eLibrary.

Abstract

Mud Pulse Telemetry (MPT) is the most common down hole-to-surface communication technology utilized by MWD/LWD systems. Compared to alternative technologies, MPT systems are characterized by a proven record of high reliability in a wide range of operating environments. Reliable data delivery is feasible in a variety of scenarios ranging from shallow vertical to complex, deep water wells in all types of drilling fluid media.

Recent years have seen the introduction of many new LWD technologies which are providing unparalleled amounts of wire-line quality evaluation data in realtime. Access to high quality, complete, evaluation data sets whilst drilling is enabling geologists and engineers to make decisions with higher confidence based on more and higher quality datasets, consequently enabling wells to become more complex and fulfill multiple objectives. The ever increasing volume of information generated by these new technologies has begun to exceed the bandwidth transmission capacity that traditional MPT technology can deliver. To fully capitalize on the LWD technological advances being implemented, an increase in data transmission speeds is required.

This paper discusses a new telemetry system that delivers data rates in excess of 6 bits per second (bps). The system has been deployed in a number of complex 3D extended reach offshore wells in Norway. During operations, the system reliably delivered high data rates of up to 20 bps, resulting in improved drilling efficiency, and reduced operational risk due to enhanced realtime decision quality based on the improved quality of FE and downhole diagnostics data.

Introduction

As with any other data communication system, the quest for higher data rates comes down to increasing the overall system Signal-to-Noise Ratio (SNR). The higher this ratio, the higher the transmission speeds that can be achieved. An increase in SNR can only be obtained by increasing signal strength, decreasing noise, or a combination of both. One obvious means to increase signal strength is to increase the downhole pulse pressure generated by the pulser valve. In reality, when transmitting at higher data rates with traditional pulser designs, lower downhole pressure pulses are generates as there is less time available to induce a pulse wave into the mud column. The SNR can also be improved by decreasing the noise power at the receiver system. This is usually accomplished by applying specific, noise source dependent signal processing algorithms. During operations, operational parameters affecting the transmissions quality vary. In order to account for changes in Signalto- Noise-Ratios and to maximize the transmission speeds, it is advantageous to be able to switch transmission modes and signal frequencies as needed during operations.

In this paper we discuss a new Mud Pulse Telemetry System that addresses SNR optimization and system flexibility for increased mud pulse telemetry data rates. The new system comprises of a novel downhole pulser and surface signal processing equipment and algorithms. The system has been successfully deployed in a variety of wells offshore Norway. During this work high communication speeds of up to 20 bps were achieved that enabled the operators to have more detailed realtime data available to improve the drilling process and, ultimately, reduce risks.

In the next section we briefly describe the signal processing parts of the new system design and discuss the advantage of added flexibility for increased system reliability. We then describe the operator's challenges on two wells drilled offshore Norway and point out how the new Mud Pulse Telemetry System was used to overcome them. Particular focus is put on Reservoir Navigation and Drilling Optimization aspects - both critical areas when striving towards a reduction in operational risks.

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