DEVELOPMENT OF INDUCTION LOGGING DEVICE

Abstract

Use of induction Logging method is very important for sub-surface exploration of rockmass, like Groundwater, Petro leum Oil and Natural Gases and other minerals in the rock formation. It is done through the measurement of formation conductivity by Induction Method. Other methods of conducti vity /Resistivity logging are by using Current and Potential Electrodes, making galvanic contacts with the formation. The galvanic method suffers from the error due to loose contact and the flow of current through the invaded zones which con tributes to the distribution of current through the formation and consequent Potential difference, picked up through the potential electrodes. However, Induction Logging Technique thus? far used have the inherent shortcoming/limitation due to the Non-linearity of response and shrinkage of the 'Depth of Investigation' and the variation in Transmitter current with the rise in the formation conductivity. This introduces error between the 'measured' or 'apparent' conductivity and the 'true' conduc tivity of the formation. An attempt has been made in this thesis of developing New Induction Logging Technique by introducing the new ideas of normalised output and Multi Frequency Logging to retain the 'Depth of investigation' and making the response Piecewise linear. The final output of the Signal Processing Unit in the existing Induction Logging Equipment is the In-phase compo nent to the Transmitter current of the Receiver coil E.M.F. This component of E.M.F. is proportional to both, the forma tion conductivity and Transmitter current,, Thus due to the variation of the Transmitter current, especially in high con ductivity region of formation, serious error is introduced in the final measurement, and Induction Logging Technique fails to log the high conductivity regions. By deriving the output, normalised of the Transmitter current, the above error is entirely eliminated. Applications of Well-logging and various Well-logging techniques have been described in Chapter One before coming to the Induction Logging Technique. The Scientific background, which forms the basis of the Induction Logging Technique, has been discussed in Chapter Two. This chapter also covers the concept of axial and radial focussing to pick up the response from the circularring section of interest out of the whole rockmass. Chapter Three presents the New Instrumentation scheme based on the final relationship between the formation conduc tivity and the Active component of the Receiver coil E.M.F., as derived in the last chapter. A Six-coil Induction Log ging Sonde (6Fl) is designed and developed. The Transmitter and Receiver coils have been designed for the maximum sensitivity within the geometrical constraints of the Sonde, and their positioning on the mandrel. vi An expected theoretical response of the above sonde has been evaluated through the uefcof computer and Change over points of the operating frequency vs. the final norma lised output presented in the Tabular form to develop the idea of Multi-Frequency Logging. Chapter Four of the thesis gives the design of the Electronic Device for Multi-Frequency Legging alongwith the relevant circuit diagrams of the various subunits (Blocks). Test results of various blocks like Multi-Frequency oscillator (showing Input reference voltage vs. output fre quency of the oscillator, and output voltage), and testing the performance of the device at 20 KHz;- Power Amplifier (giving Input D.C. Power, output A.C. Power, Transmitter current and voltage)} Low Level Signal amplifier (the per formance showing Input-output voltages) and Signal Proces sing Unit - D.C. testing of various sections of the unit as well as complete unit, and A.C. testing of the complete unit , are given in Chapter Five. This chapter also includes the testing of Six Coil induction Logging sonde for its radial induction and focussing capabilities. Discussions on the performance of the device while con sidering the various blocks and the future scope of work to realise the fruits of the development of the new Induction Logging Scheme have been made in the Chapter Six. Chapter Seven concludes the successful completion of the development- -of Induction Logging Device.