Page 9 - Geothermal Energy Systems Exploration, Development, and Utilization

Contents VII

3 Drilling into Geothermal Reservoirs 113
Axel Sperber, Inga Moeck, and Wulf Brandt
3.1 Introduction 113
3.1.1 Geothermal Environments and General Tasks 114
3.2 Drilling Equipment and Techniques 115
3.2.1 Rigs and Their Basic Concepts 115
3.2.1.1 Hoisting System 115
3.2.1.2 Top Drive or Rotary Table 115
3.2.1.3 Mud Pumps 116
3.2.1.4 Solids Control Equipment 118
3.2.1.5 Blowout Preventer (BOP) 118
3.2.2 Drillstring 118
3.2.2.1 Bottomhole Assembly 118
3.2.2.2 Drillpipe 121
3.2.3 Directional Drilling 122
3.2.3.1 Downhole Motor (DHM) 122
3.2.3.2 Rotary Steerable Systems (RSS) 122
3.2.3.3 Downhole Measuring System (MWD) with Signal Transmission Unit
(Pulser) 123
3.2.3.4 Surface Receiver to Receive and Decode the Pulser Signals 123
3.2.3.5 Special Computer Program to Evaluate Where the Bottom of the Hole
Is at Survey Depth 123
3.2.4 Coring 125
3.3 Drilling Mud 125
3.3.1 Mud Types 126
3.3.1.1 Water-based Mud 126
3.3.1.2 Oil-based Mud 126
3.3.1.3 Foams 126
3.3.1.4 Air 126
3.3.2 The Importance of Mud Technology in Certain Geological
Environments 127
3.3.2.1 Drilling through Plastic/Creeping Formations (Salt, Clay) 127
3.3.2.2 Formation Pressure and Formation Damage (Hydrostatic Head,
ECD) 127
3.4 Casing and Cementation 128
3.4.1 Casing and Liner Concepts 129
3.4.2 Casing Materials 129
3.4.3 Pipe Centralization 131
3.4.4 Cementation 132
3.4.5 Cement Slurries, ECD 133
3.4.6 Influence of Temperature on Casing and Cement 136
3.5 Planning a Well 136
3.5.1 Geological Forecast 136
3.5.1.1 Target Definition 137
3.5.1.2 Pore Pressures/Fracture Pressure/Temperature 137