For developing the available hydrocarbon reserves and for exploring new reservoirs, deeper and more complex wells are drilled. Drilling such deeper and complex wells requires a constant monitoring and controlling of the well paths. Therefore, the bottom hole assembly, the lower section of the drill string above the drill bit, is equipped with numerous measuring sensors for collecting geological and directional data while drilling. The collected data have to be transmitted to the surface in real time. Prior to transmit the data measured downhole to the surface, they are processed and translated into a binary code. Accordingly, the data will be represented as a series of zeroes and ones. The most common method for data transmission in boreholes is the so called mud pulse telemetry which sends the information through the drilling mud inside the drill string by means of coded pressure pulses. There are two types of devices available for downhole pressure pulses generation. The first type is the (positive or negative) pressure pulser which transmits the data by quasi-static variations of the pressure level inside the drill string. The second type is the (rotating or oscillating) mud siren which transmits the data by generating continuous pressure waves at specific frequencies. The main disadvantage of the mud pulse telemetry is its low data transmission rate which is about 10 bps. This data rate is very low compared to the measured amount of raw data. Therefore, the efficiency of the mud pulse telemetry must be improved, so that the data could be transmitted at higher rates. The present research work presents different developed and tested concepts for increasing the efficiency and the data transmission rate of the mud pulse telemetry. Both, the transmitter and the receiver end, were taken into consideration by developing the new concepts. Different hardware and software tools were used for performing the present research work. The available flow loop test facility and the experimental prototypes of the mud siren and positive pulser were used. The test facility was extended in order to enable the investigation of the new concepts. The available 3D numerical model (ANSYS CFX) was modified and extended in order to study the new concepts. At the transmitter end, a novel concept for a hybrid mud pulse telemetry system was developed and successfully tested. Here, two different types of mud pulse telemetry could be used in a combination, such as a mud siren and a pressure pulser. The developed concept was registered at the German Patent and Trade Mark Office for a patent in 2018. Two concepts for a multi-frequency mud siren were developed for simultaneous generation of two frequencies. In the first approach, two sets of stator/rotor were installed in a row connection, while they were installed in a parallel connection in the second approach. The two concepts were registered at the German Patent and Trade Mark Office for patents in 2015. An experimental multi-frequency generator was built and used for testing of several new ideas, such as transmitting the data using several carrier frequencies at the same time, transmitting the data with different wave forms (sine, sawtooth, triangle and rectangle), or transmitting the data using the chirp modulation. The innovative design of the experimental multi-frequency generator was registered at the German Patent and Trade Mark Office for patents in 2016. At the receiver end, two different methods for processing and analyzing the received multi-frequency signals using the Wavelet and Fourier analysis were drafted and tested. A novel concept for the use of a multi-sensor receiver was developed and successfully tested. The use of a multi-sensor receiver could strongly improve the detection of the received signals.:Table of Contents Declaration ii Abstract iii Acknowledgements v Table of Contents vi List of Abbreviations x List of Symbols xii CHAPTER 1 Introduction 1 CHAPTER 2 Modern Drilling Technology and Low Data Transmission Rate as a Limitation 5 2.1 Introduction to the modern drilling technology 5 2.1.1 Directional drilling technology 5 2.1.2 Steering technology 6 2.1.3 Measuring technology 8 2.1.4 Technology of data transmission in boreholes 9 2.2 Low data transmission rate as a problem with respect to the whole drilling process 13 CHAPTER 3 Fundamentals of Communication Technology 16 3.1 Modulation techniques for data transmission in baseband 16 3.2 Modulation techniques for data transmission in passband 17 3.3 Multiple frequency and chirp spread spectrum modulation techniques 19 3.4 Digital signal processing 21 3.4.1 Fourier transformation 21 3.4.2 Continuous wavelet transformation 23 3.4.3 Filtering 24 CHAPTER 4 State of the Art for Mud Pulse Telemetry Systems 26 4.1 Historical development of mud pulse telemetry including latest improvements applied for increasing its data transmission rate 26 4.2 Available types of mud pulse telemetry devices 30 4.2.1 Negative pulser 31 4.2.2 Positive pulser 32 4.2.3 Mud siren 32 4.2.4 Oscillating shear valve 33 4.3 Limitations of data transmission via mud pulse telemetry 34 4.3.1 Effect of noise sources in the mud channel on the transmission signal 34 4.3.2 Effect of attenuation in the mud channel on the transmission signal 36 4.3.3 Effect of reflections and their interference with the main transmission signal 37 4.3.4 Pass and stop bands 38 4.4.5 Minimum transmission time slot 38 CHAPTER 5 Novel Concepts and Tools for Increased Data Transmission Rates of Mud Pulse Telemetry 40 5.1 Transmitter end 41 5.1.1 Hybrid mud pulse telemetry (HMPT) 41 5.1.2 Multi-frequency generator 43 5.2 Receiver end 45 5.2.1 Investigation of the Wavelet analysis suitability for multi-frequency signal detection 45 5.2.2 Flexible placement of multi-sensor receiver 46 CHAPTER 6 Laboratory Test Facility and Used Hard and Soft Tools 49 6.1 Laboratory test facility for hydraulic data transmission in boreholes 49 6.2 Experimental prototypes of the pressure pulsers and mud siren 53 6.3 3D numerical simulation model for the test facility and mud siren 55 6.4 MATLAB software 58 CHAPTER 7 Hybrid Mud Pulse Telemetry (HMPT) System 59 7.1 Combination of mud siren and negative pressure pulser 60 7.2 Combination of mud siren and positive pressure pulser 63 7.3 Evaluating the laboratory investigations of the hybrid mud pulse telemetry (HMPT) system 66 CHAPTER 8 Mathematical and Numerical Investigation of the Concept of the Multi-Frequency Mud Siren 68 8.1 Preliminary considerations for the concept of the multi-frequency mud siren 69 8.2 Mathematical model investigation of different approaches for the multi-frequency mud siren concept 71 8.2.1 Multi-frequency mud siren with stators and rotors in a row 72 8.2.2 Multi-frequency mud siren with parallel connection of stators and rotors 74 8.3 Numerical model investigation of multi-frequency mud siren with two sets of stator/rotor in a row 77 8.3.1 Numerical simulations for data transmission with a multi-frequency mud siren using two carrier frequencies 79 8.3.2 Evaluation of the simulation results 81 8.3.3 Increasing the transmission reach of the mud siren for deep drilling operations 83 CHAPTER 9 Laboratory Investigations of Multi-Carrier Hydraulic Data Transmission Using an Experimental Multi-Frequency Generator 85 9.1 Laboratory multi-carrier frequency transmission tests 87 9.2 Investigation of the Wavelet analysis suitability for the detection of multi-frequency signal transmitted in boreholes 95 9.3 Initial investigations of hydraulic data transmission using chirp modulation and different pressure wave forms 100 9.3.1 Data transmission using chirp modulation (Chirp Spread Spectrum, CSS) 100 9.3.2 Data transmission using different wave forms 101 CHAPTER 10 Investigation of the Use of a Multi-Sensor Receiver for Improving the Hydraulic Data Transmission in Boreholes 104 10.1 Numerical model investigation of the use of a multi-sensor receiver 104 10.1.1 Data transmission using single-input and multiple-output (SIMO) 104 10.1.2 Data transmission using multiple-input and multiple-output (MIMO) 107 10.2 Laboratory investigations of the use of a multi-sensor receiver 108 10.3 Evaluating the use of a multi-sensor receiver for improving the hydraulic data transmission in boreholes 112 CHAPTER 11 Conclusion and Outlook 116 11.1 Conclusion 116 11.2 Outlook 120 References 122 List of Figures 129 List of Tables 136 List of Publications 137 List of Patents 138 Appendix- Chapter 7 139 Appendix- Chapter 8 141 Appendix- Chapter 9 142 Appendix- Chapter 10 146