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Applied Drilling Engineering Adam T. Bourgoyne Jr. Professor of Petroleum Engineering, Louisiana State U. Keith K. Millheim Manager —Critical Drilling Facility, Amoco Production Co. Martin E. Chenevert Senior Lecturer of Petroleum Engineering, U. of Texas F.S. Young Jr. President, Woodway Energy Co. First Printing Society of Petroleum Engineers Richardson, TX 1986 Dedication This book is dedicated to the many students who were forced to study from trial drafis of this work. Copyright 1986 by the Society of Petroleum Engineers. Printed in thc United States of America. AN rights reserved. This book, or parts thereof, cannot be reproduced in any form without written consent of the publisher. ISBN 1-55563-001-4 Acknowledgments The authors would like to acknowledge the help of individuals and companies in the oil- and gas-producing industry that are too numerous to mention. Without the unselfish help of so many, this book would not have been possible. In particular, the American Petrole- um Inst, the Intl. Assn. of Drilling Contraetors, and the Peiroleum Extension Service of the U. of Texas were of tremendous assistance in providing background material for several chapters. Special thanks are due numerous individuals who have served on the SPE Textbook Committee during the past decade for their help and understanding. In particular, a large contribution was made by Jack Evers of the U. of Wyoming. who served for several years on the Texibook Committee as senior revicwer and coordinator tor this work. Finally, the authors would like to recognize the contribution of Dan Adamson, SPE Executive Direc- tor, who constantly prodded the authors to ““finish the book.” Adam T. Bourgoyne Jr. When I accepted the challenge of writing part of this textboek, [ had no idea of how much of my free time would be consumed. There were many evenings, weckends, and even holidays and vacations when I was busy writing. correcting, or editing. I thank Valerie, my wife, for the understanding and patience in letting me complete this monumental! task. 1 would like to extend my gratitude to Allen Sinor for his dedicated effort in helping me with our part of the textbook. If 1 were not for Allen, E doubt I could have completed it. 1 would also like to thank John Horeth II, Warren Winters, Mark Dunbar, and Tommy Warren for their assistance with the problems and examples: Amoco Production Co. for permission to write part af this textbook: and the research staff in Tulsa that helped with the typing and drafting. Keith K. Millheim Kt is impossible for me 10 list the many people to whom ! am indebted for their assistance in the preparation of my part of this book. The many meetings, discussions, and work sessions 1 had with my drilling industry associates span a period of 8 years and are too numerous to recall. For their assistance I am thankful. 1 would also particularly like to thank the U. of Texas and SPE for their encouragement and support. Martin E, Chenevert The Society of Petroleum Engineers Textbook Series is made possible in part by grants from the Shell Companies Foundation and the SPE Foundation. SPE SPE Foundation SPE Textbook Series The Textbook Series of the Society of Petroleum Engineers was established in 1972 by action of the SPE Board of Directors. The Series is intended to ensure availability of high- quality textbooks for use in undergraduate courses in arcas clearly identified as being within the petreleum engineering ficld. The work is directed by the Society's Textbook Commit- tee, one of more than 50 Society-wide standing committees, through members designated as Texthook Editors. The Textbook Editors and the Textbook Committee provide techni- cal evaluation of the book. Below is a listing of those who have been most closely in- volved in the final preparation of this book. Many others contributed as Textbook Committee members or athers involved with the book. Textbook Editors Jack F. Evers, U. of Wyoming David S. Pye, Union Geothermal Div. Textbook Committee (1984) Medhat Kamal, chairman. Flopetro!-Johnston Jack Evers, U. of Wyoming Steve Pye, Union Oil Co. of California H.M. Staggs, ARCO Oil & Gas Co. L. Kent Thomas, Phillips Petroleum Co. Fred H. Poetimann, Colorado School of Mines Theodore Blevins, Chevron U.S.A. Philip Schenewerk, ENSERCH Exploration Wilmer A. Hoyer, Exxon Production Research Co. Steve Neuse, Hudson Consultants Inc. Rotary Drilling Drilling Team Drilling Rigs Rig Power System Hoisting System Circulating System The Rotary System The Well Control System Well-Monitoring System Special Marine Equipment 1.10 Drilling Cost Analysis Exercises LR 1. 1. 1, 1. 1 1. 1. 1. vaginais Drilling Fluids 2.1 Diagnostic Tests 2.2 Pilot Tests 2.3 Water-Base Muds 2.4 Inhibitive Water-Base Muds 2.5 Oil Muds Exercises Cements 3.1 Composition of Portland Cement 3.2 Cement Testing 3.3 Standardization of Drilling Cements 3.4 Cement Additives 3.5 Cement Placement Techniques Exercises Drilling Hydraulics 4.1 Hydrostatic Pressure in Liquid Columns 4.2 Hydrostatic Pressure in Gas Columns 4.3 Hydrostatic Pressure in Complex Fluid Columns 4.4 Annular Pressures During Well Control Operations 4.5 Buoyancy 4.6 Nonstatic Well Conditions 4.7 Flow Through Jet Bits 4.8 Rheological Models 4.9 Rotational Viscometer 4.10 Laminar Flow in Pipes and Annuli 4.11 Turbulent Flow in Pipes and Annuli 4.12 Initiating Circulation of the Well 4.13 Jet Bit Nozzle Size Selection 4.14 Pump Pressure Schedules for Well Control Operations 4.15 Surge Pressures Due to Vertical Pipe Movement 4.16 Particle Slip Velocity Exercises Rotary Drilling Bits 5.1 Bit Types Available 5.2 Rock Failure Mechanisms Contents Bau — 17 24 26 27 32 3 42 54 2 75 82 8s 86 89 0 103 no 13 14 19 122 127 129 131 135 137 154 156 162 164 173 183 190 200 5.3 Bit Selection and Evaluation 209 5.4 Factors Affecting Tooth Wear 214 5.5 Factors Affecting Bearing Wear 219 5.6 Terminating a Bit Run 220 5.7 Factors Affecting Penetration Rate 21 5.8 Bit Operation 236 Exercises 240 6. Formation Pore Pressure and Fracture Resistance 6.1 Formation Pore Pressure 246 6.2 Methods for Estimating Pore Pressure 252 6.3 Formation Fracture Resistance 285 6.4 Methods for Estimating Fracture Pressure 287 Exercises 294 7. Casing Design 7.1 Manufacture of Casing 301 7.2 Standardization of Casing 302 7.3 API Casing Performance Properties 305 74 Casing Design Criteria 330 7.5 Special Design Considerations 339 Exercises 348 8. Directional Drilling and Deviation Control 8.1 Definitions and Reasons for Dircctional Drilling 351 8.2 Planning the Directional Well Trajectory 353 8.3 Calculating the Trajectory of a Well 362 8.4 Planning the Kickoff and Trajectory Change 366 8.5 Dircctional Drilling Measurements 377 8.6 Deflection Tools 402 8.7 Principles of the BHA 426 8.8 Deviation Control 443 Exercises 453 Appendix A: Development of Equations for Non-Newtonian Liquids in a Rotational Viscometer Bingham Plastic Model 474 Power-Law Model 476 Appendix B: Development of Slot Flow Approximations for Annular Fiow for Non-Newtonian Fluids Bingham Plastic Model am Power-Law Model 481 Author Index 484 Subject Index 486 o 2 APPLIED DRILLING ENGINEERING Courtesy o! Texaco Inc. 8 z 2 z a 5 2 8 Fig. 1.1 — Texaco drilling barge Gibbens on location in Fig. 1.2- Man-made ice platform in deep water area of Lafitte field, Louisiana. the Canadian Arctic Islands. OL ORILLINE ORILLING COMPANY SERVICES CONTRACTOR (well Oparator) COMPANIES [ L [ [ li [ACCOUNTING RIG DESIGN & ACCOUNTING | RESERVOIR LAND DEPARTMENT) | [MAINTENANCE DEPARTMENT) | | ENGINEERING DEPARTMENT) [GaIINE | | [omcLIaS FLUIDS CEMENTS DRILLING FORMATION PRODUCTION WELL | | |FORMATION MONITORING] [EVALUATION DRILLING SUPERINTENDENT DIRECTIONAL DRILLING DRILLING ENGINEERING e —" SEOLO6Y | DRILLING WELL, — + nu BITS COMPLETION|. e EQUIPMENT ARA COMPANY REPRESENTATIVE oTnER RIGS OTHER WELLS ALOWOUT Nise ] IN PROGRESS H CONTRACT = e PREVENTION] — E — —— FIELD REPRESENTATIVES, oermoiman] [EAR RIG CREW Fig. 1.3- Typica! drilling rig organizations. ROTARY DRILLING PROCESS Derek, «Rotary Mose pa y -.-Stana Pipa Blowaut Prevantoe 4 Emergan Elom me ROTARY DRILLING RIGS [eorrom supronr] [FLoatins, l [Eeuisueversiate] [omc.swr] [conventionaL] [uosice | xceme] [FoRmas.E wasr] BARGE| | JACKUP Fig. 1.4- The rotary drilling process. 1.2 Drilling Rigs Rotary drilling rigs are used for almost alt drilling done today. A sketch illustrating the rotary drilling process is shown in Fig. 1.4. The hole is drilled by rotating a bit to which a downward force is applied. Generalily, the bit is turned by rotating the entire drilistring, using a rotary table at the surface, and the downward force is applied to the bit by using sections of heavy thick-walled pipe, called drill collars, in the drillstring above the bit. The cuttings are lifted to the surface by circulating a fluid down the drillstring, through the bit, and up the annular space between the hole and the drilstring. The cuttings are separated from the drilling fluid at the surface. As shown in Fig. 1.5, rotary drilling rigs can be classified broadly as land rigs or marine rigs. The main design features of land rigs are portability and maximum operating depth. The derrick of the conventional land rig must be built on location. In many cases the derrick is left over the hole after the well is completed. In the early days of drilling, many of these standard derricks were built quite close togethe a field was developed. However, because of the cost of construction, most modern land rigs are built so that the derrick can be moved easily and reused. The various rig components are skid- mounted so that the rig can be moved in units and connected easily. The jackknife, or cantilever, derrick (Fig. 1.6) is assembled on the ground with pins and then raised as a unit using the rig-hoisting equipment. The portable mast (Fig. 1.7), which is suitable for moderate-depth wells, usually is mounted on whecled trucks or trailers that in- corporate the hoisting machinery, engines, and q SELF CONTAINED Fig. 1.5—Classification of rotary drilling rigs. derrick as a single unit. The telescoped portable mast is raised to the vertical position and then extended to full height by hydraulic pistons on the unit. The main design features of marine rigs are portability and maximum water depth of operation. Submersible drilling barges generally are used for inland water drilling where wave action is not severe and water depths are less than about 20 ft. The entire rig is assembled on the barge, and the unit is towed to the location and sunk by flooding the barge. Once drilling is completed, the water is pumped from the barge, allowing it to be moved to the next location. After the well is completed, a platform must be built to protect the wellhead and to support the surface production equipment. In some cases, the operating water depth has been extended to about 40 ft by resting the barge on a shell mat built on the seafloor. Offshore exploratory drilling usually is done using self-contained rigs that can be moved easily. When water depth is less than about 350 ft, bottom- supported rigs can be used. The most common type of bottom-supported mobile rig is the jackup (Fig. 1.8). The jackup rig is towed to location with the legs elevated. On location, the legs are lowered to the bottom and the platform is “jacked up” above the wave action by means of hydraulic jacks. Semisubmersible rigs that can be flooded similar to an inland barge can drill resting on bottom as well as in a floating position. However, modern semisub- mersible rigs (Fig. 1.9) are usually more expensive than jackup rigs and, thus, are used mostly in water depths too great for resting on bottom. At present, most semisubmersible rigs are anchored over the hole. A few semisubmersible rigs employ large engines to position the rig over the hole dynamically. This can extend greatly the maximum operating water depth. Some of these rigs can be used in water ROTARY DRILLING PROCESS can be drilled are built and placed on location. The platforms are placed so that wellbores fanning out in all directions from the platform can develop the reservoir fully. The various rig components usually are integrated into a few large modules that a derrick barge quickly can place on the platform, Large platforms allow the use of a self-contained rig-i.e., all rig components are located on the platform (Fig. 1.11). A platform/tender combination can be used for small platforms. The rig tender, which is a floating vessel anchored next to the platform, contains the living quarters and many of the rig components (Fig. 1.12). The rig-up time and operating cost will be less for a platform/tender operation. However, some operating time may be lost during severe weather. Platform cost rises very rapidly with water depth. When water depths are too great for the economical use of development platforms, the development wells can be drilled from floating vessels, and the wellhead equipment installed on the ocean floor. Underwater completion technology is still relatively new and experimental. Although drilling rigs differ greatly in outward appearance and method of deployment, all rotary rigs have the same basic drilling equipment. The main component parts of a rotary rig are the (1) power system, (2) hoisting system, (3) fluid- circulating system, (4) rotary system, (5) well control system, and (6) well monitoring system. 1.3 Rig Power System Most rig power is consumed by the hoisting and fluid circulating systems. The other rig systems have much smaller power requirements. Fortunately, the hoisting and circulating systems generally are not used simultaneously, so the same engines can per- form both functions. Total power requirements for most rigs are from 1,000 to 3,000 hp. The early drilling rigs were powered primarily by steam. However, because of high fuel consumption and lack of portability of the large boiler plants required, steam-powered rigs have become impractical. Modern rigs are powered by internal-combustion diesel engines and generally subciassified as (1) the diesel-electric type or (2) the direct-drive type, depending on the method used to transmit power to the various rig systems. Diesel-electriç rigs are those in which the main rig engines are used to generate electricity. Electric power is transmitted easily to the various rig systems, where the required work is accomplished through use of electric motors. Direct-current motors can be wired to give a wide range of speed-torque charac- teristics that are extremely well-suited for the hoisting and circulating operations. The rig components can be packaged as portable units that can be connected with plug-in electric cable connectors. There is considerable flexibility of equipment placement, allowing better space utilization and weight distribution. In addition, electric power allows the use of a relatively simple and flexible control system. The driller can apply power smoothly to various rig Fig. 1.11 self-contained platform rig on location in the Eugene Island area, offshore Louisiana. Fig. 1.12—A tendered platform rig.!2 54) OS8X9] jo Ásaundo TABLE 1.1 = HEATING VALUE OF VARIOUS FUELS Cm (10) Fuel Density —Heating Value Type Ubmigaly (Btuflom) diesel 72 18,000 gasoline 66 20,000 butane 47 21,000 methane — 24,000 Frictionless ( o) Pulley P=wT N=rev/min 2mN)-(rr) F| po Éd.r = 27rNF Fig. 1.13— Engine power output. N Bringing in Single À From Back Swinging the Swivel & ; | Kelly Over Single for ab 1 ei 1 Mouse Hole Connection andina the Adgda | APPLIED DRILLING ENGINEERING components, thus minimizing shock and vibration problems. Direct-drive rigs accomplish power transmission from the internal combustion engines using gears, chains, belts, and clutches rather than generators and motors, The initial cost of a direct-drive power system generally is considerably less than that of a comparable diesel-electric system. The development of hydraulic drives has improved greatly the per- formance of this type of power system. Hydraulic drives reduce the shock and vibrational problems of the direct-drive system. Torque converters, which are hydraulic drives designed so that output torque increases rapidly with output load, are now used to extend the speed-torque characteristic of the internal combustion engine over greater ranges that are better suited to drilling applications. The use of torque converters also allows the selection of engines based on running conditions rather than starting con- ditions. Power-system performance characteristics generally are stated in terms of output horsepower, torque, and fuel consumption for various engine speeds. As illustrated in Fig. 1.13, the shaft power developed by an engine is obtained from the product of the angular velocity of the shaft, «, and the output torque T; The overall power efficiency determines the rate of fuel consumption wyat a given engine speed. The heating values H of various fuels for internal combustion engines are shown in Table 1.1. The heat energy input to the engine, Q,, can be expressed by [o RO é AR (1.2) Since the overall power system efficiency, E, is defined as the energy output per energy input, then p E=>. 2; Todos g (1.3) || Singte Into Top || “Si oie or Dri Pi 4 : E e “Single Added & Ready to Make New Hole Fig. 1.44 — Making a connection.'? APPLIED DRILLING ENGINEERING Traveling Block Draw as O = / Anchor Storage Reet / t (a) Arrangement and nomenciature of block and tackle. b) Free body diagram of traveling block. nF, (c) Free body diagram of crown block Fig. 1.16 — Schematic of block and tackle. pipe that can be handled and, thus, the faster a long string of pipe can be inserted in or removed from the hole. The most commonty used drillpipe is between 27 and 30 ft long. Derricks that can handle sections called stands, which are composed of two, three, or four joints of drillpipe, are said to be capable of pulling doubles, thribbles, or fourbles, respectively. In addition to their height, derricks are rated according to their ability to withstand compressive loads and wind loads. Allowable wind loads usually are specified both with the drillstring in the hole and with the drillstring standing in sections in the derrick. When the drillstring is standing in the derrick resting against the pipe-racking platform, an overturning moment is applied to the derrick at that point. Wind ratings must be computed assuming wind loading is in the same direction as this overtumning moment. An- chored guy wires attached to each leg of the derrick are used to increase the wind rating of small portable masts. The American Petroleum Institute (API) has published standards dealing with derrick specifications and ratings. !3 To provide working space below the derrick floor for pressure control valves called biowout preventers, the derrick usually is elevated above the ground level by placement on a substructure. The substructure must support not only the derrick with its load but also the weight of other large pieces of equipment. API Bull. Dt0! recommends rating substructure load-supporting capacity according to (1) the maximum pipe weight that can “be set back in the derrick, (2) the maximum pipe weight that can be suspended in the rotary table (irrespective of setback load), and (3) the corner loading capacity (maximum supportable load at each corner). Also, in API Standard 4A,! three substructure types have been adopted. In addition, many non-API designs are available. The choice of design usually is governed by blowout preventer height and local soil conditions. 1.4.2 Block and Tackle. The block and tackle is comprised of (1) the crown block, (2) the traveling block, and (3) the drilling line. The arrangement and mnomenclature of the block and tackle used on rotary rigs are shown in Fig. 1.16a. The principal function of the block and tackle is to provide a mechanical advantage, which permits easier handling of large loads. The mechanical advantage M of a block and tackle is simply the load supported by the traveling block, W, divided by the load imposed on the drawworks, Fr The load imposed on the drawworks is the tension in the fast line. The idea! mechanical advantage, which assumes no friction in the block and tackle, can be determined from a force analysis of the traveling block. Consider the free body diagram of the traveling block as shown in Fig. 1.16b. If there is no friction in the pulleys, the tension in the drilling line is constant throughout. Thus, a force balance in the vertical direction yields nF,=W, where n is the number of lines strung through the ROTARY DRILLING PROCESS TABLE 1.2 — AVERAGE EFFICIENCY FACTORS FOR BLOCK-AND:TACKLE SYSTEM Number of Lines Efficiency im 8 0.874 8 0.841 10 0.810 12 0.770 14 0.740 traveling block. Solving this relationship for the tension in the fast line and substituting the resulting expression in Eg. 1.4 yields w win" which indicates that the ideal mechanical advantage is equal to the number of lines strung between the crown block and traveling block. Eight lines are shown between the crown block and traveling block in Fig. 1.16. The use of 6, 8, 10, or 12 lines is com- mon, depending on the loading condition. The input power P, of the block and tackle is equal to the drawworks load F, a times the velocity of the fast line, v;: The output power, or Rook power, P, is equal to the traveling block load W times the velocity of the traveling block, v,: (1.6) For a frictionless block and tackle, W=nF,. Also, since the movement of the fast line by a unit distance tends to shorten each of the lines strung between the crown block and traveling block by only 1/n times the unit distance, then v, =v,/n. Thus, a frictionless system implies that the ratio of output power to input power is unity: po Ph - (nF o) (upin) =. P; For Of course, in an actual system, there is always a power loss due to friction. Approximate values of block and tackle efficiency for roller-bearing sheaves are shown in Table 1.2. Knowledge of the block and tackle efficiency permits calculation of the actual tension in the fast line for a given load. Since the power efficiency is given by Pr Wo Wogin W Po Far Fry Epn” 9 Derrick “| 8 Leg “= Dead Line Lines to Block .... e... / Line 6 c D Fig. 1.17 — Projection of drilling lines on rig floor. then the tension in the fast line is Ww F=—. En Eq. 1.7 can be used to select drilling line size. However, a safety factor should be used to allow for line wear and shock loading conditions. The line arrangement used on the block and tackle causes the load imposed on the derrick to be greater than the hook load. As shown in Fig. 1.16c, the load Fy applied to the derrick is the sum of the hook load W, the tension in the dead line, F,, and the tension in the fast line, Fp F4W+EG4E,. Ifthe load, W, is being hoisted by pulling on the fast line, the friction in the sheaves is resisting the motion of the fast line and the tension in the drilling line increases from W/n at the first sheave (deadline) to W; En at the last sheave (fast line). Substituting these values for F and F, in Eq. |.8a gives Wo Ww (LtEtEn FasW+ — + — = W. 4 mta En ) (18%) The total derrick load is not distributed equally over all four derrick legs. Since the drawworks is located on one side of the derrick floor, the tension in the fast line is distributed over only two of the four derrick legs. Also, the dead line affects only the leg to which it is attached. The drilling lines usually are arranged as in the plan view of the rig floor shown in Fig. 1.17. For this arrangement, derrick Legs € and D would share the load imposed by the tension in the fast line and Leg A would assume the full load im- posed by the tension in the dead line. The load ROTARY DRILLING PROCESS most severe stress at these points. The lap points are the points in the drilling line where a new layer or lap of wire begins on the drum of the drawworks, Drilling line is maintained in good condition by following a scheduled stip-and-cut program. Slipping the drilling line involves loosening the dead line anchor and placing a few feet of new line in service from the storage reel. Cutting the drilling line in- volves removing the line from the drum of the drawworks and cutting off a section of line from the end. Slipping the line changes the pickup points, and cutting the line changes the lap points. The line is sometimes slipped several times before it is cut. Care must be taken not to slip the line a multiple of the distance between pickup points. Otherwise, points of maximum wear are just shifted from one sheave to the next. Likewise, care must be taken when cutting the line not to cut a section equal in length to a multiple of the distance between lap points. API!8 has adopted a slip-and-cut program for drilling lines. The parameter adopted to evaluate the amount of line service is the son-mile. A drilling line is said to have rendered one ton-mile of service when the traveling block has moved 1 U.S. ton a distance of 1 mile. Note that for simplicity this parameter is independent of the number of lines strung. Ton-mile records must be maintained in order to employ a satisfactory slip-and-cut program. Devices that automatically accumulate the ton-miles of service are available. The number of ton-miles between cutoffs will vary with drilling conditions and drilling line diameter and must be determined through field experience. In hard rock drilling, vibrational problems may cause more rapid line wear than when the rock types are relatively soft. Typical ton-miles between cutoff usually range from about 500 for 1-in.-diameter drilling line to about 2,000 for 1.375-in.-diameter drilling line. Example 1.2. A rig must hoist a load of 300,000 Ibf. The drawworks can provide an input power to the block and tackle system as high as 500 hp. Eight lines are strung between the crown block and traveling block. Calculate (1) the static tension in the fast line when upward motion is impending, (2) the maximum hook horsepower available, (3) the maximum hoisting speed, (4) the actual derrick load, (5) the maximum equivalent derrick load, and (6) the derrick efficiency factor. Assume that the rig floor is arranged as shown in Fig. 1.17. Solution. 1. The power efficiency for n= 8 is given as 0.841 in Table 1.2. The tension in the fast line is given by Eg. 1.7. Ff = W 100,000 = ST En” 0.841 (8) = t4S90 IDE. 2. The maximum hook horsepower available is Py=E-p;=0.841 (500)= 420.5 hp. 3. The maximum hoisting speed is given by 33,000 ft-Ibf/min 420.5hp (2) Pro hp Up= w = 300,000 Ibf =46.3 ft/min. To pull a 90-ft stand would require 90 ft = — = = 1 ,9min. 46.3 ft/min 4. The actual derrick load is given by Eq. 1.8b: pa( E yy o ( 1+0.841+0.841(8) ZITO) ) (300,00) =382,090 Ibf. 5. The maximum equivalent load is given by Eg. 1,9: au= (04 B+4 —) W= — (300,000) = 450,000 Ibf. n 8 6. The derrick efficiency factor is Fa. 382,090 E= 2 MO o gg or 849%. dE Fg 450,00 er stato 1.4.3 Drawworks, The drawworks (Fig. 1.19) pro- vide the hoisting and braking power required to raise or lower the heavy strings of pipe. The principal parts of the drawworks are (1) the drum, (2) the brakes, (3) the transmission, and (4) the catheads. The drum transmits the torque required for hoisting or braking. It also stores the drilling line required to move the traveling block the length of the derrick. The brakes must have the capacity to stop and sustain the great weights imposcd when lowcring a string of pipe into the hole. Auxiliary brakes are used to help dissipate the large amount of heat generated during braking. Two types of auxiliary brakes commonly used are (1) the hydrodynamic type and (2) the electromagnetic type. For the hydrodynamic type, braking is provided by water being impelled in a direction opposite to the rotation of the drum. In the electromagnetic type, electrical braking is provided by two opposing magnetic fields. The magnitude of the magnetic fields is dependent on the speed of rotation and the amount of external excitation current supplied. In both types, the heat developed must be dissipated by a liquid cooling system. The drawworks transmission provides a means for easily changing the direction and speed of the traveling block. Power also must be transmitted to catheads attached to both ends of the drawworks. Courtesy ot ARMCO Nat]. Supply Co. Fig. 1.19 Example drawworks used in rotary drilling. Fig. 1.21—Tongs powered by chain to cathead. APPLIED DRILLING ENGINEERING Friction catheads shown in Fig. 1.20 turn con- tinuously and can be used to assist in lifting or moving equipment on the rig floor. The number of turns of rope on the drum and the tension provided by the operator controls the force of the pull. A second type of cathead generally located between the drawworks housing and the friction cathead can be used to provide the torque needed to screw or un- screw sections of pipe. Fig. 1.21 shows a joint of drillpipe being tightened with tongs powered by a chain from the cathead. Hydraulically or air- powered spinning and torquing devices also are available as alternatives to the conventional tongs. One type of power tong is shown in Fig. 1.22. 1.5 Circulating System A major function of the fluid-circulating system is to remove the rock cuttings from the hole as drilling progresses. A schematic diagram illustrating a typical rig circulating system is shown in Fig. 1.23. The drilling fluid is most commonly a suspension of clay and other materials in water and is called drilting mud. The drilling mud travels (1) from the steel tanks to the mud pump, (2) from the pump through the high-pressure surface connections to the drillstring, (3) through the drillstring to the bit, (4) through the nozzles of the bit and up the annular space between the drilistring and hole to the surface, and (5) through the contaminant-removal equipment back to the suction tank. The principal components of the rig circulating system include (1) mud pumps, (2) mud pits, (3) mud- mixing equipment, and (4) contaminant-removal equipment. With the exception of several ex- perimental types, mud pumps always have used reciprocating positive-displacement pistons. Both two-cylinder (duplex) and three-cylinder (triplex) pumps are common, The duplex pumps generally are double-acting pumps that pump on both forward and backward piston strokes. The triplex pumps generally are single-acting pumps that pump only on forward piston strokes. Triplex pumps are lighter and more compact than duplex pumps, their output pressure pulsations are not as great, and they are cheaper to operate. For these reasons, the majority of new pumps being placed into operation are of the triplex design. The advantages of the reciprocating positive- displacement pump are the (1) ability to move high- solids-content fluids laden with abrasives, (2) ability to pump large particles, (3) ease of operation and maintenance, (4) reliability, and (5) ability to operate over a wide range of pressures and flow rates by changing the diameters of the pump liners (compres- sion cylinders) and pistons. Example duplex and triplex mud pumps are shown in Fig. 1.24. The overall efficiency of a mud-circulating pump is the product of the mechanical efficiency and the volumetric efficiency. Mechanical efficiency usually is assumed to be 90% and is related to the efficiency of the prime mover itself and the linkage to the pump drive shaft. Volumetric efficiency of a pump whose 
