SPE Production & Operations
Volume 22, Number 1, February 2007, pp. 128-134

Summary

A coreless electromagnetic coupling-based telemetry system for well-test data involving a full-bore drillstem test apparatus has been developed. This system allows the retrieval of formation pressures and temperatures above and below a tester valve by means of a wireline-conveyed electronic gauge and a permanently installed gauge. A wireline-deployed coreless electromagnetic proximity sonde is put into the well to transfer the data using time-division frequency transmission technology in the “Synchronization-Pressure-Low-Temperature-Low” mode on a single-core wired-armored cable. The coded pulse data are modulated on DC power signals. The surface processor uses a double-counter synchronization method to measure signal frequencies to eliminate ±1 most significant bit (MSB) error. Then a simplified algorithm is proposed, based on least-squares curve fitting and dimension-reduction methods, for computing actual temperatures and pressures for analysis of well-testing data. The proposed system is calibrated for temperatures up to 125°C and pressures up to 70 MPa with a pressure accuracy of 0.1% full scale (FS) and temperature accuracy of ±0.5°C. This approach combines the advantages of drillstem testing and wireline formation testing and has been successfully applied to onshore well testing.

Introduction

In oil and gas well testing, it is important to obtain accurate real-time pressures and temperatures from the bottom of a well. The need for surface-to-downhole communication in this context has long been recognized, and many techniques have been proposed, including wireline telemetry (Whittle et al. 2003), permanently installed downhole monitoring systems (Veneruso et al. 2000), and wireless telemetry (“Electromagnetic” 200l; Tochikawa et al. 1996). The wireline telemetry system provides higher data rates than other currently used methods. However, it requires that the sensitive measurement gauges endure long-term exposure to an extremely hostile environment. The permanently installed downhole monitoring system records data in a module that is retrieved after the tubing is lifted from the hole. However, this method makes it difficult to collect real-time data. Wireless telemetry involves either extremely low-frequency electromagnetic (EM) wave transmission through the formation or acoustic transmission through the drillstring. The propagation of EM waves is characterized by an increase in attenuation with increases in distance, data rate, and ground conductivity (Trofimenkoff et al. 2000). Therefore, current EM telemetry systems are practical only for land operations where the resistivities are greater than 1 ohm-m and the target formation is shallow (Soulier 2003). Though Halliburton has recently developed an acoustic telemetry data acquisition system (Harperet al. 2003), it is limited by its high energy consumption and the complicated problems caused by the lengthwise variations of drillstems. This paper describes a coreless EM coupling-based telemetry system equipped with two electronic gauges which provide users with access to real-time downhole data above and below the tester valve during drillstem testing operations.

© 2007. Society of Petroleum Engineers

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History

• Original manuscript received: 2 August 2005
• Revised manuscript received: 29 March 2006
• Manuscript approved: 29 March 2006
• Version of record: 20 February 2007