k&m erd textbook, 3rd edition

Drilling Design and Implementation for Extended Reach and Complex Wells

Published by K&M TECHNOLOGY GROUP, LLC

Houston, Texas 2003

Contributing Authors Mike Mims Tony Krepp

1997- 2003 by K&M Technology Group, LLC All rights reserved Third Edition Printed in the United States of America This book or parts thereof may not be reproduced in any form without permission of K&M Technology Group, LLC, Houston, Texas. Brand names, company names, trademarks, or other identifying symbols appearing in illustrations and text are used for educational purposes only and do not constitute an endorsement by the authors, editor, or publisher.

Drilling Design and Implementation for ER and Complex Wells

2007 Third Edition Page 2

TABLE OF CONTENTS

1 INTRODUCTION ............................................................................................................................... 9

2 PURPOSE & SCOPE ........................................................................................................................ 12

3 WHAT IS EXTENDED REACH DRILLING ................................................................................ 14

3.1 ERD DEFINITIONS ...................................................................................................................... 15

4 WHATS DIFFERENT ABOUT ERD ............................................................................................ 18

4.1 GENERAL ERD DIFFERENCES ..................................................................................................... 18 4.2 SPECIFIC SHALLOW ERD WELL DIFFERENCES ............................................................................ 26 4.3 SPECIFIC LONG ERD WELL DIFFERENCES .................................................................................. 27 4.4 SPECIFIC DEEP WATER ERD WELL DIFFERENCES ....................................................................... 28

5 PLANNING ERD WELLS ............................................................................................................... 30

5.1 ORGANIZATIONAL STRUCTURE ................................................................................................... 30 5.2 ERD PROJECT PLANNING OUTLINE ............................................................................................. 31 5.3 RISK MANAGEMENT ................................................................................................................... 34

5.3.1 Aggressive Strategies to Reduce Risk .......................................................................... 36 5.4 RIG CAPABILITY ......................................................................................................................... 37

5.4.1 Hydraulics Capability ...................................................................................................... 39 5.4.2 Rotary and Hoisting Capability ....................................................................................... 40 5.4.3 Power Capability ............................................................................................................. 40 5.4.4 General Rig Capabilities .................................................................................................. 41

5.5 ERD PLANNING GENERAL REQUIREMENTS .............................................................................. 44 5.5.1 Hole Size Selection ........................................................................................................... 44 5.5.2 Wellpath Design ............................................................................................................... 45

5.5.2.1 Build and Hold Profile ................................................................................................. 45 5.5.2.2 Catenary Profile ........................................................................................................... 46 5.5.2.3 S-Turn Profile .............................................................................................................. 48 5.5.2.4 Complex 3-D Well Designs ......................................................................................... 48

5.5.3 Casing Design .................................................................................................................. 49 5.5.3.1 Casing Depths .............................................................................................................. 49 5.5.3.2 Casing Running ........................................................................................................... 49 5.5.3.3 Casing Wear ................................................................................................................ 50 5.5.3.4 Hydraulics Issues ......................................................................................................... 52

5.5.4 Drilling Fluids Selection .................................................................................................. 52 5.5.5 Wellbore Stability ............................................................................................................. 56 5.5.6 Hole Cleaning .................................................................................................................. 57 5.5.7 Torque and Drag Modeling .............................................................................................. 61 5.5.8 Directional Drilling Strategy ........................................................................................... 62 5.5.9 Negative Weight Wells ..................................................................................................... 64 5.5.10 Drillstring Design ............................................................................................................ 64

5.5.10.1 General Drillstring and BHA design....................................................................... 64 5.5.10.2 Drillpipe size ........................................................................................................... 65 5.5.10.3 Other Drillstring Specifications .............................................................................. 67 5.5.10.4 Integral Bladed Drillpipe ........................................................................................ 68 5.5.10.5 High Friction Pipe Dope ......................................................................................... 68

5.5.11 Surveying and Targets ...................................................................................................... 68 5.5.11.1 Targets and Geological Uncertainty ....................................................................... 69

5.5.12 Formation evaluation ....................................................................................................... 70 5.5.13 Cementing ........................................................................................................................ 72

6 HOLE CLEANING ........................................................................................................................... 73



6.1 FUNDAMENTALS OF HOLE CLEANING ......................................................................................... 73 6.1.1 Cuttings Transportation.................................................................................................... 73 6.1.2 What is Happening Downhole? ........................................................................................ 74 6.1.3 Systems Approach ............................................................................................................. 76 6.1.4 What is a Clean Hole? ................................................................................................. 78 6.1.5 How is the Hole Cleaned? ................................................................................................ 80

6.1.5.1 Rotation ........................................................................................................................ 80 6.1.5.2 Flowrate ....................................................................................................................... 81 6.1.5.3 Fluid Rheology ............................................................................................................ 82 6.1.5.4 Bottoms-up .................................................................................................................. 83

6.2 GUIDELINES FOR HOLE CLEANING WHILE DRILLING .................................................................. 84 6.2.1 Drilling Fluids .................................................................................................................. 84

6.2.1.1 Rheology Guidelines .................................................................................................... 84 6.2.1.2 OWR Guidelines .......................................................................................................... 85 6.2.1.3 Low Gravity Solids ...................................................................................................... 85

6.2.2 Flowrates and hydraulics ................................................................................................. 85 6.2.3 Drillpipe Rotation ............................................................................................................. 87 6.2.4 Connection Practices ........................................................................................................ 88 6.2.5 Monitoring Hole Cleaning Performance .......................................................................... 89

6.2.5.1 Drilling in The Box ...................................................................................................... 89 6.2.5.2 Off-bottom Torque and Drag (T&D) Data ................................................................... 92 6.2.5.3 Cuttings Returns .......................................................................................................... 95 6.2.5.4 Drilling Parameters ...................................................................................................... 95 6.2.5.5 Mud Properties ............................................................................................................. 95 6.2.5.6 Downhole Tools ........................................................................................................... 96

6.3 GUIDELINES FOR CLEANUP PRIOR TO TRIPPING .......................................................................... 98 6.4 GUIDELINES FOR TRIPPING .......................................................................................................... 99

6.4.1 Standard Tripping Procedure ........................................................................................... 99 6.4.2 Backreaming ................................................................................................................... 100

6.4.2.1 Guidelines for Back-Reaming through a Tight Spot ............................................... 103 6.4.2.2 Guidelines for Precautionary Backreaming ............................................................... 103

6.5 GUIDELINES FOR REMEDIAL HOLE CLEANING .......................................................................... 104 6.5.1 Stop and Circulate .......................................................................................................... 105 6.5.2 Wiper Trips ..................................................................................................................... 105 6.5.3 Sweeps ............................................................................................................................ 105 6.5.4 Backreaming ................................................................................................................... 107

7 TORQUE, DRAG, BUCKLING AND VIBRATIONS ................................................................. 108

7.1 TORQUE AND DRAG THEORY .................................................................................................... 108 7.1.1 Torque............................................................................................................................. 110 7.1.2 Drag ................................................................................................................................ 111 7.1.3 Friction Factors .............................................................................................................. 111

7.1.3.1 Planning Friction Factors ........................................................................................... 113 7.1.3.2 Sensitivity Analysis ................................................................................................... 114

7.1.4 General Torque and Drag Definitions ............................................................................ 116 7.2 WELLPATH DESIGN ................................................................................................................... 116

7.2.1 Catenary Well Profile ..................................................................................................... 117 7.2.2 S-Turn Profile ................................................................................................................. 117 7.2.3 Complex 3-D Well Designs ............................................................................................. 118

7.3 KEY WELL INTERVALS FROM A TORQUE, DRAG AND BUCKLING VIEWPOINT ........................... 119 7.3.1 Shallow Build Section ..................................................................................................... 119 7.3.2 Tangent Section .............................................................................................................. 121 7.3.3 Lower Build and Turn Section ........................................................................................ 122 7.3.4 Lower Drop Section ........................................................................................................ 122 7.3.5 Reservoir / 8" Section .................................................................................................. 122

7.4 BUCKLING ................................................................................................................................. 123



7.4.1 Buckling Theory ............................................................................................................. 123 7.4.1.1 Sinusoidal (or snaky) Buckling .............................................................................. 126 7.4.1.2 Helical (or Coiled Spring) Buckling ...................................................................... 126 7.4.1.3 Common Misconceptions .......................................................................................... 127

7.4.2 Common Buckling Intervals ........................................................................................... 127 7.4.3 Options to Prevent or Reduce Buckling ......................................................................... 129

7.4.3.1 Wellpath Design ........................................................................................................ 129 7.4.3.2 Drillpipe Size and Stiffness ....................................................................................... 129 7.4.3.3 Special Downhole Tools to Improve Drillpipe Stiffness ........................................... 130 7.4.3.4 Rotation and Flotation ............................................................................................... 131

7.5 VIBRATIONS ............................................................................................................................. 132 7.5.1 Types of Vibrations ........................................................................................................ 132

8 NEGATIVE WEIGHT WELLS .................................................................................................... 134

8.1 DRILLING OPERATIONS ............................................................................................................ 134 8.1.1 Drillstring Design .......................................................................................................... 134 8.1.2 Tripping In ..................................................................................................................... 135 8.1.3 Drilling ........................................................................................................................... 135 8.1.4 Deep Sliding Technique ................................................................................................. 136 8.1.5 Drilling with Block Weight ............................................................................................. 137

8.2 CASING RUNNING OPERATIONS ................................................................................................ 137 8.2.1 First Line Contingencies ................................................................................................ 138

8.2.1.1 Lighter Weight Casing .............................................................................................. 138 8.2.1.2 Inverted Casing Designs ............................................................................................ 138 8.2.1.3 Hangoff Drill collars .................................................................................................. 139 8.2.1.4 Run Casing as a Liner................................................................................................ 139 8.2.1.5 Apply Top Drive Weight ........................................................................................... 139 8.2.1.6 Top Drive Pull-Down Systems .................................................................................. 141

8.2.2 Casing Floatation Techniques ....................................................................................... 142 8.2.2.1 Air Filled (Empty) ..................................................................................................... 143 8.2.2.2 Mud Over Air ............................................................................................................ 145 8.2.2.3 Air Cavity Technique ................................................................................................ 145 8.2.2.4 Heavy Mud Over Light Mud ..................................................................................... 146

9 HYDRAULICS PLANNING .......................................................................................................... 147

9.1 HYDRAULICS MODELING .......................................................................................................... 147 9.2 OPTIMIZATION OF HYDRAULICS PERFORMANCE ...................................................................... 147

9.2.1 Identify Rig Hydraulic Limitations ................................................................................. 147 9.2.2 Well Design .................................................................................................................... 148 9.2.3 Drilling Fluid ................................................................................................................. 149 9.2.4 Drillstring Design .......................................................................................................... 150

9.2.4.1 Drillpipe Size ............................................................................................................. 150 9.2.4.2 Tooljoint Design and Dimensions ............................................................................. 154 9.2.4.3 HWDP Length ........................................................................................................... 154

9.2.5 BHA Design .................................................................................................................... 154 9.2.5.1 MWD / FEWD Selection ........................................................................................... 155 9.2.5.2 Adjustable Stabilizers ................................................................................................ 155 9.2.5.3 Rotary Steerable Tools .............................................................................................. 155 9.2.5.4 Steerable Motors with PDC bits ................................................................................ 156 9.2.5.5 Steerable Motors with Tricone Bits ........................................................................... 156

9.2.6 Bit Hydraulics ................................................................................................................ 157 9.2.6.1 PDC Bits .................................................................................................................... 157 9.2.6.2 Tri-cone Bits .............................................................................................................. 157

10 ECD MANAGEMENT .............................................................................................................. 158

10.1 WHAT IS ECD .......................................................................................................................... 158



10.1.1 ECD and pipe rotation.................................................................................................... 159 10.2 WHAT ARE THE EFFECTS OF ECD ............................................................................................. 160 10.3 WHY IS ECD A PARTICULAR CONCERN FOR ERD ..................................................................... 161 10.4 EXAMPLES OF ECD MAGNITUDES ............................................................................................ 162 10.5 ECD MANAGEMENT PLANNING PHASE .................................................................................. 163

10.5.1 Wellpath Design ............................................................................................................. 164 10.5.2 Hole Size Optimization ................................................................................................... 164 10.5.3 Casing Plan .................................................................................................................... 165

10.5.3.1 Run Intermediate Casing as a Liner ...................................................................... 165 10.5.3.2 Use Alternative Casing Connections and Centralizers .......................................... 165 10.5.3.3 Use different sizes of casing.................................................................................. 166 10.5.3.4 Casing Flotation and ECD .................................................................................... 166

10.5.4 Drilling Fluids ................................................................................................................ 166 10.5.4.1 Rheologies ............................................................................................................. 166 10.5.4.2 Gel Strengths ......................................................................................................... 167 10.5.4.3 Sweeps .................................................................................................................. 167

10.5.5 Drillstring Design ........................................................................................................... 168 10.5.6 Bit and stabilizer design ................................................................................................. 169 10.5.7 Pressure While Drilling (PWD) Technology .................................................................. 169

10.6 ECD MANAGEMENT OPERATIONAL PHASE............................................................................ 169 10.6.1 Flowrate and RPM ......................................................................................................... 169 10.6.2 ROP ................................................................................................................................ 170 10.6.3 Slide Drilling Practices .................................................................................................. 170 10.6.4 Backreaming ................................................................................................................... 171 10.6.5 Down-Reaming ............................................................................................................... 171 10.6.6 Tripping Practices .......................................................................................................... 171 10.6.7 Summary of ECD Management in Operational Phase ................................................... 172

11 DIRECTIONAL DRILLING STRATEGIES .......................................................................... 174

11.1 PRIORITIES FOR DIRECTIONAL DRILLERS .................................................................................. 174 11.2 PLANNING BHA STRATEGY ...................................................................................................... 175

11.2.1 Key Issue Hole Cleaning ............................................................................................. 176 11.2.2 Key Issue Hydraulics ................................................................................................... 176 11.2.3 Key Issue Directional Control Required ...................................................................... 177 11.2.4 Key Issue Tortuosity .................................................................................................... 177 11.2.5 Key Issue Torque, Drag and Buckling ......................................................................... 178 11.2.6 Key Issue Bit Selection ................................................................................................. 178 11.2.7 Key Issue Overall Drilling Cost and Efficiency ........................................................... 179

11.3 SPECIFIC MOTOR ISSUES ........................................................................................................... 182 11.4 BHA ALTERNATIVES ........................................................................................................... 183

11.4.1 Shallow Build Sections ................................................................................................... 184 11.4.2 Tangent Sections ............................................................................................................. 185 11.4.3 Deep Build / Drop / Turn Sections .................................................................................. 188 11.4.4 Horizontal Sections ......................................................................................................... 189

11.5 GENERAL BHA CONSIDERATIONS ............................................................................................ 192 11.5.1 Jars ................................................................................................................................. 192 11.5.2 BHA Weight .................................................................................................................... 192 11.5.3 Stabilizer Designs ........................................................................................................... 193 11.5.4 Adjustable Stabilizers ..................................................................................................... 193 11.5.5 BHA Prediction Modeling for Rotary Assemblies .......................................................... 194 11.5.6 Advanced Rotary Slide Drill Technique ......................................................................... 194 11.5.7 Chasing the Curve .......................................................................................................... 197 11.5.8 Reporting Practices ........................................................................................................ 198 11.5.9 Rotary Steerable Tools (RSTs) ...................................................................................... 199

12 BIT SELECTION STRATEGY ................................................................................................ 203



12.1 PDC BITS .................................................................................................................................. 204 12.1.1 Matrix Verses Steel Bodied ............................................................................................ 204 12.1.2 Vibration Management ................................................................................................... 205 12.1.3 PDC cutter Design and Placement ................................................................................ 205 12.1.4 Gauge Length ................................................................................................................. 205

12.2 TRI-CONE BITS ......................................................................................................................... 207 12.3 BI-CENTER BITS ....................................................................................................................... 207 12.4 RST BITS .................................................................................................................................. 209 12.5 BIT HYDRAULICS ...................................................................................................................... 209 12.6 BIT SELECTION FOR STEERABLE APPLICATIONS ....................................................................... 211

13 SURVEYING AND GEOLOGICAL UNCERTAINTY MANAGEMENT .......................... 213

13.1 THEORY AND DEFINITIONS ....................................................................................................... 213 13.1.1 Confidence Interval ........................................................................................................ 214 13.1.2 MWD Operation and Uncertainties ............................................................................... 215 13.1.3 Gyro Operation and Uncertainties ................................................................................. 216 13.1.4 Random and Systematic Errors ...................................................................................... 217 13.1.5 Survey Interval ............................................................................................................... 217

13.2 OPTIONS TO REDUCE SURVEY UNCERTAINTY ........................................................................... 218 13.2.1 MWD Surveys ................................................................................................................. 218 13.2.2 Gyro Surveys .................................................................................................................. 219 13.2.3 In-Hole Referencing (IHR) ............................................................................................. 219 13.2.4 In-Field Referencing (IFR) ............................................................................................. 220 13.2.5 Geosteering .................................................................................................................... 220

13.3 TARGET DESIGN ....................................................................................................................... 220 13.3.1 Target Size and Shape .................................................................................................... 220 13.3.2 Allow for the Survey Uncertainty ................................................................................... 223

13.4 REDUCING GEOLOGICAL UNCERTAINTY ................................................................................... 224

14 CEMENTING ............................................................................................................................. 225

14.1 DISPLACEMENT INSIDE CASING ................................................................................................ 225 14.2 DISPLACEMENT OUTSIDE CASING ............................................................................................ 226 14.3 CEMENTING CASING ................................................................................................................. 227 14.4 CEMENTING LINERS ................................................................................................................. 228 14.5 OPEN HOLE CEMENT PLUGS ..................................................................................................... 229 14.6 SLURRY DESIGN ....................................................................................................................... 230 14.7 SPACER TRAINS ........................................................................................................................ 232 14.8 ECD ISSUES.............................................................................................................................. 233 14.9 CASING CENTRALIZATION ........................................................................................................ 234

15 WELL CONTROL ..................................................................................................................... 235

15.1 WELL CONTROL BASICS ........................................................................................................... 235 15.2 WELL CONTROL - WHATS DIFFERENT ABOUT ERD WELLS ................................................... 238

15.2.1 Taking a Kick ................................................................................................................. 238 15.2.2 Detecting a Kick ............................................................................................................. 239 15.2.3 Killing a Well ................................................................................................................. 240 15.2.4 Other Differences ........................................................................................................... 240

15.3 KILLING ERD WELLS ............................................................................................................... 241 15.3.1 Wait and Weight Method ................................................................................................ 241 15.3.2 The Drillers Method ....................................................................................................... 242 15.3.3 Engineers Method .......................................................................................................... 242

15.4 VERTICAL AND DEVIATED KILL SHEETS .................................................................................. 243

16 DEEPWATER ERD WELLS .................................................................................................... 244

16.1 RISER ISSUES ............................................................................................................................ 245 16.2 ECD ISSUES.............................................................................................................................. 246



16.3 BUILD SECTION ISSUES ............................................................................................................. 246

17 COMPLETIONS AND WORKOVERS IN ERD .................................................................... 248

18 SPECIALTY TOOLS AND NEW TECHNOLOGIES ........................................................... 250

18.1 DIRECTIONAL DRILLING ........................................................................................................... 250 18.1.1 Rotary Steerable Tools ................................................................................................... 250 18.1.2 Adjustable Stabilizers ..................................................................................................... 250 18.1.3 Steerable Motors ............................................................................................................. 251 18.1.4 Rotating Near Bit Stabilizers .......................................................................................... 251 18.1.5 Pin Down Motors ............................................................................................................ 252 18.1.6 At-Bit Inclination Tools .................................................................................................. 252 18.1.7 Steerable Turbines .......................................................................................................... 253 18.1.8 Walking Bits .................................................................................................................... 253 18.1.9 Downhole Thrusters ....................................................................................................... 254 18.1.10 AG-itator .................................................................................................................... 254 18.1.11 Anaconda ................................................................................................................... 254 18.1.12 Drop Gyros ............................................................................................................... 254

18.2 MWD TECHNOLOGY ................................................................................................................ 254 18.2.1 Directional MWD ........................................................................................................... 255 18.2.2 MWD Directional Survey Accuracy ............................................................................... 255 18.2.3 Real Time Multi-Axis Vibrations .................................................................................... 255 18.2.4 Real Time Downhole Annular Pressure (Pressure While Drilling) ........................... 256 18.2.5 Downhole WOB / Downhole Torque .............................................................................. 257 18.2.6 MWD Caliper ................................................................................................................. 257 18.2.7 MWD Gyros .................................................................................................................. 258

18.3 CASING AND CEMENTING ......................................................................................................... 258 18.3.1 Expandable Slotted Casing ............................................................................................. 258 18.3.2 High Torque Casing Connections................................................................................... 259 18.3.3 Casing Shoes .................................................................................................................. 259

18.4 DRILLPIPE ................................................................................................................................. 260 18.4.1 5 Drillpipe Premium High Torque drillpipe .............................................................. 260 18.4.2 Integral Bladed Drillpipe ............................................................................................... 260 18.4.3 165 ksi High Strength Material Drillpipe ....................................................................... 260 18.4.4 Composite and Titanium Drillpipe ................................................................................. 261 18.4.5 Pin-Up Drillpipe ............................................................................................................. 261

18.5 HOLE CLEANING ....................................................................................................................... 261 18.5.1 Integral Bladed Drillpipe ............................................................................................... 261 18.5.2 Hydraulic By-Pass Sub ................................................................................................... 262

18.6 TORQUE REDUCTION ................................................................................................................ 262 18.6.1 Non Rotating Drillpipe Protectors ................................................................................. 262 18.6.2 Roller Bearing Subs ........................................................................................................ 263

19 EXAMPLES OF OPTIMIZED ERD WELL DESIGNS ......................................................... 264

19.1 EXAMPLE #1: ERD PROJECT, UKRAINE .................................................................................... 264 19.2 EXAMPLE #2: SHALLOW ERD PROJECT, OFFSHORE WEST AFRICA .......................................... 267 19.3 EXAMPLE #3: INFILL ERD WELL, OFFSHORE AUSTRALIA ........................................................ 271 19.4 EXAMPLE #4: ERD SATELLITE DEVELOPMENT, OFFSHORE AUSTRALIA ................................... 275 19.5 EXAMPLE #5: SIGNIFICANT PROBLEMS ON ERD WELLS, OFFSHORE AUSTRALIA ..................... 278

20 RELEVANT TECHNICAL PUBLICATIONS ........................................................................ 280

20.1 ER DRILLING - GENERAL .......................................................................................................... 280 20.2 HOLE CLEANING IN ERD .......................................................................................................... 285 20.3 TORQUE, DRAG AND BUCKLING ............................................................................................... 286 20.4 HYDRAULICS AND ECDS / PRESSURE WHILE DRILLING .......................................................... 289 20.5 DIRECTIONAL DRILLING ........................................................................................................... 290



20.6 DRILLPIPE ................................................................................................................................. 292 20.7 DOWNHOLE VIBRATION ........................................................................................................... 293 20.8 CASING WEAR .......................................................................................................................... 294 20.9 SURVEYING .............................................................................................................................. 294 20.10 CEMENTING IN ERD ............................................................................................................ 295 20.11 WELL CONTROL IN HIGH ANGLE WELLBORES .................................................................... 296 20.12 COMPLETIONS IN ERD ......................................................................................................... 296



1 INTRODUCTION The following manual has been compiled by K&M Technology Group as a training aid for ERD and Complex Well Drilling Engineering and Practices. This text has been written for presentation to attendees of the K&M Horizontal and ERD Drilling Induction Training (H.E.R.D.I.T.) course and will be used as the course text. This is the 3rd edition of the text and it outlines the latest technologies and practices utilized in ERD planning, drilling and completions. About the authors: This text has been compiled by Michael Mims, President and CEO, Tony Krepp, Vice President of Engineering, Harry Williams, Vice President of Training, and Russell Conwell, Senior Drilling Engineer for K&M Technology Group. Mike, Tony and Russell are based in Houston, Texas, while Harry is based in Perth, Australia. Mike first became involved in ERD drilling during the Unocal Pt. Pedernales Project and has since participated in many of the worlds high profile ERD projects. Mike holds more than 10 patents on ERD technologies and continues to use and develop leading edge technologies in his clients well designs. Tony has been involved in numerous ERD and horizontal projects for K&M in Australia, Canada, Eastern Europe, USA and Africa. Tonys specialties are in well designing for optimized performance and application of downhole technologies (especially bits, directional drilling, MWD and logging technologies). He has played a key role in many innovative ERD and horizontal design solutions while participating in K&M projects. Harry joined K&M after retiring from Exxon, where he was involved in drilling their record breaking ERD wells. He has a broad background in drilling operations and has developed a number of training aides that are currently being used worldwide. Russell has been involved in ERD projects in Australia, USA, Russia and China, while working with Exxon, Woodside and K&M. He has a strong operations background, recently being involved as the lead Operations Engineer for the longest well in the world drilled from a platform. All of these gentlemen have planned and participated in numerous record breaking ERD wells. They are all currently involved in regional and world record projects that will set new benchmarks for drilling performance and depth.



About K&M: K&M Technology Group is a Houston, Texas based company with operations currently active in the USA, Australia, New Zealand, West Africa, China, Norway, Russia and the UK. K&M was founded in 1988 when its founder, Michael Mims, became involved in the development of leading edge technologies for extended reach wells for UNOCAL in California. K&Ms technical services have since expanded to include software development, training programs and well site surveillance services; all aimed at improving drilling performance in complex well environments. Though the company was originally formed in California, it moved its central operations to Perth, Western Australia in 1992. K&M's mission is to lead the oil & gas industry in the development and application of leading edge extended reach technology. K&M's technological advances became so greatly recognized by 1997 that some of its largest clients requested K&M to bring its technology back into the U.S. market. K&M services are now offered worldwide to clients such as Exxon, Chevron, BP, Esso, Shell, Texaco and Apache, to name a few. K&M has been involved in extended reach and horizontal drilling from its inception. In early 1989, K&M were contracted to design and build a special liner system for one of the first extended reach drilling programs for Unocal. With this development of additional technology, the company was thrust further into the new and technically complex world of extended reach drilling. K&M's accomplishments in the extended reach field have been chronicled on numerous fronts, such as winning the prestigious Australian Institute of Engineers, Engineering Excellence Award for accomplishments in the field of extended reach drilling and with numerous worldwide patents. K&M has played a variety of roles in the design, drilling and completion in a wide range of complex projects. With the recognition K&M has received from its contribution on record setting wells, clients often involve K&M very early in the stages of field development. This work includes studies ranging from simple feasibility studies to comprehensive development plans, including detailed well designs and economic analysis. K&M continues to work for many of the world's major oil companies on difficult, complex drilling projects. K&M's state-of-the-art expertise and its team of highly skilled engineers have enabled the company to offer a wide range of technical and training services. K&M is involved in projects internationally where its teams are acting in roles from Field Surveillance Engineers to Lead Design Engineers to Total Project Management Teams. K&M has also performed the role of "troubleshooter" on many extended reach and horizontal wells. Innovative technical designs have proven to be K&M's specialty in this field. Special casing running procedures, drill string torque reducing techniques and torque & drag computer software are just a few of K&M's technical innovations. K&M engineers hold more than a dozen patents, worldwide, for these technologies.



K&M also offers a range of training services as well as drilling engineering and design software systems. The training services have been heralded as the most advanced drilling performance schools in the industry. Through the experience gained in the development and application of leading edge technology in their client wells, K&M's training schools help to reduce the learning curve in advanced drilling programs. The engineers who are developing and applying these advanced techniques teach K&Ms courses. These courses are designed fit-for-purpose to the clients operations with content that is taken from the classroom and applied immediately in the field. K&Ms core team of experts has helped it to become a full service provider of technical services to the drilling industry. K&M's development of leading edge technology in the complex world of extended reach and horizontal drilling has helped it to become a recognized leader in the industry. For more information visit our website at: www.kmtechnology.com



2 PURPOSE & SCOPE The purpose of this training manual is to capture the current best practices and available technologies for ERD and complex well drilling planning and implementation. This manual is intended for use primarily by engineers and senior operations personnel and as a text for the participants in the H.E.R.D.I.T courses. This text assumes that the reader has a degree of competency in drilling engineering and drilling operations practices. With input from this text, the reader will be able to apply current practices to ERD and complex well programs and issue detailed program operational instructions. Note that many of the design ideas that are proposed in this document are not necessarily conventional, however almost all of the principles and practices are based on real experience. The authors have had particular success over the past decade with challenging the normand therefore make no apologies for proposing solutions that may not appear in other ERD manuals. Nor will we back off from our posture of critiquing conventional thinking as this has helped to shed many of the hog laws that tend to haunt our operational practices. The overall theme of this text is to educate engineering and operations personnel with respect to what is really happening down the hole in ERD and complex wells. Additionally, we hope to encourage the reader to think of the ERD drilling and completion operations as a complex system and to use a systems approach towards reaching design solutions. This method encourages innovative and fit-for-purpose designs, rather than adopting the usual off of the shelf solution. Many readers may find that some of the suggestions and comments contradict those practices already successfully used in some ERD projects and so would quite rightly ask:

Why should I consider such non-conventional strategies when the conventional approach is already in successful use? In many cases, K&M would answer that (a) the well times could have been much faster and less expensive, (b) that the practices necessitated much larger rig capability than could have been used.

Similarly, another fair question is if such savings can be made, or if much smaller rigs can be used by utilizing alternate drilling strategies, then why arent these techniques in much more common use? There are numerous reasons for this, some of which are as simple as lack of experienced people that ask why do we do it this way, or simply that it is not in the interests of key service companies to suggest alternate methods. However, probably the most important reason is that it requires significant planning work, both on a project and a well-by-well basis, to implement real optimization to the drilling performance. It is K&Ms experience that few Operators or service companies have, or take the time to plan their work sufficiently, whereas it is much easier (at least in the pre-spud period) to simply adopt the past solution.



The manual is set out in the following structure which attempts to present this complex and detailed subject as simply as possible:

SECTION SUBJECT PURPOSE

3 What is ERD?

Define what an ERD well is and provide an overview of what has been done in the

industry

4 What is different about ERD?

Highlight the main differences from

conventional wells

5 Planning ERD wells

Overview of the planning process for an

ERD well

6-18 Detailed Discussion of various issues and their relation to ERD

The theoretical and practical planning

considerations for the main ERD issues

19 Examples

Examples of how ERD wells have been

optimized

20 Reference

Listing of relevant SPE papers for further

investigation

The authors recognize that many of the discussions within this manual overlap each other and there may appear to be some redundancy. This is intentional because most of the topics are closely inter-linked, so it is difficult and inappropriate to discuss subjects in isolation.



3 WHAT IS EXTENDED REACH DRILLING Drilling technology has advanced rapidly in the last 5-10 years. As can be seen in Figure 1 below, the 10 km reach barrier has been now been surpassed three times and several Operators are actively planning wells from 11-15 km reach. As well as the very long wells, there is also a move to drill further with complex well designs such as big-bore, designer wells, deepwater and other emerging technologies (i.e. expandables, multilaterals, etc.). Traditionally, an ERD well has been defined as a well with a Horizontal/Total Vertical Depth (HD/TVD) ratio > 2.0. The HD/TVD ratio has also been used to provide a relative measure of the complexity of an ERD well (i.e. the higher the ratio, the more complex and difficult the well). However, this definition does not fully capture the different types of ERD wells, or the relative complexity of each. The following section aims to provide a categorization of ERD wells, based firstly on their well profile and secondly on some of their unique complexities.

Figure: 1 Industry ERD Wells Drilled to Date

INDUSTRY ERD EXPERIENCE

0

1000

2000

3000

4000

5000

6000

7000

80000 2,000 4,000 6,000 8,000 10,000 12,000

Horizontal Throw (m)

TVD

(m)

Straight lines represent horizontal throw to vertical

depth ratio

5.0

4.0

3.0

2.0

1.0

6.0



3.1 ERD DEFINITIONS There are two basic types of ERD wells, which are primarily defined by the well profile:

1. Very shallow wells 2. Very long wells

Figure: 2 Two Basic Types of ERD Wells

Very long ERD wells are the type of well design that is usually envisaged when Extended Reach is mentioned. Very shallow ERD wells have quite unique problems and are often equally as challenging. Whereas very long ERD wells must overcome forces and pressures of high magnitude (i.e. brute force is needed), shallow wells must often overcome buckling and drag while managing annular pressures within very small ECD limitations. In either case, it is necessary to drill smart if performance is to be optimized. In addition to the two basic ERD well types, the following specific ERD designs can also be defined:

Complex well Design Deepwater ERD Wells Limited Rig Capability

TWO BASIC TYPES OF ER WELLS

Horizontal Throw

TVD

Very Shallow ER wells:Must overcome buckling and drag, whilst dealing with low ECD limits and unconsolidated formations

5.0

4.0

3.02.01.0

6.0

Very Long ER wells:Must overcome large forces and pressures, often challenging rig limits



Complex Well Design: These 3-D well designs have mainly been drilled in the North Sea in the last few years and involve significant changes in azimuth to line the well up with the required target(s). As shown in Figure 3, the traditional HD/TVD ratio cannot be used to define the complexity of these wells, and MD/TVD ratio provides a more meaningful definition. The use of Rotary Steerable Tools (RSTs) has significantly improved the performance on these wells and allowed more complex designs to be attempted.

Figure: 3 Examples of Complex Designer Wells



Deepwater ERD Wells: With a significant increase in deepwater drilling in the last 2-3 years, there has been a move towards the drilling of ERD wells in deepwater applications. This has resulted in very challenging wells, which combine the unique difficulties of deepwater drilling, with the existing difficulties of ERD wells. The nature of deepwater drilling only serves to increase the impact of some of the existing ERD well challenges. For example, hole cleaning becomes that much more difficult with a long riser section, cold mud at the bottom of the riser impacts hydraulics and ECDs, and buckling in the long riser section limits BHA strategies. Limited Rig Capability K&M also believes that the definition of ERD should account for the capabilities of the drilling rig that will be used. In essence, a 6000m MD (20,000) high angle well may be quite straightforward with a large rig (i.e. 5 drillpipe and 3 x 1600 HP pumps), but will be a significant challenge with a small rig (i.e. 5 drillpipe and 2 x 1600 HP pumps). Today, advanced drilling technologies are being used to reduce the time and risk of drilling these long wells with small rigs. Many of the techniques that are described in this manual are those which have been developed through drilling ERD wells from rigs that are not ideally suited to ERD drilling. These technologies not only apply today in this application, but also will help to push the envelope for ERD wells out further as the larger rigs capabilities begin to be taxed.



4 WHATS DIFFERENT ABOUT ERD There are numerous issues that are different, or more critical, for ERD wells than for conventional directional wells. In some case, the challenges on ERD wells are the same as those on conventional directional wells, only magnified. In other cases, the issues are specific to the type of ERD well that is being drilled. These key differences are discussed briefly in the topics below and will be covered in detail later in the manual.

4.1 GENERAL ERD DIFFERENCES

ISSUE MAJOR ERD DIFFERENCES

TORQUE, DRAG AND BUCKLING

Torque, Drag and Buckling limitations are regularly encountered on ERD wells during both the drilling and completions phases. Completions and workovers must be included in the base well designs, since there are numerous cases where ERD wells have been successfully drilled, but cannot be completed or worked over adequately because of design flaws or workover rig limitations. Torque, drag and buckling results are directly related to the wellpath, drillstring, hole size, casing, completion and drilling fluids designs. Hole cleaning and hole conditioning are also major factors that must be considered. Excessive torque and drag often drives the well designer towards more sophisticated drilling fluids for improved lubricity.

TORQUE Torque is generally only a significant limiting factor on long ERD wells or on slim-hole ERD wells (where small diameter drillpipe will be used). It is common to rotate casing and liners strings on ERD wells to ensure that a good cement job is obtained and this is often the critical torque limitation. Torque limits can be reached in a number of ways including limits to: Top drive or rotary table output Drill pipe tooljoints Casing connections Combined power usage Efforts have been made in the industry to counter these limitations with: Stronger, more compact top drives Higher torque drill string tool joint connections High torque casing connections Subs and tools designed to reduce torque



ISSUE MAJOR ERD DIFFERENCES (CONT..)

AXIAL DRAG Axial drag occurs due to the interaction of the drillpipe or casing as it is run in (slack-off) or picked up (pick-up) out of the hole. Axial drag (pick-up and slack-off) becomes a problem as: the wells get deeper (more pipe on low side of the hole) with higher inclinations (higher vertical component of weight) as the rig gets smaller (equipment pickup and slack-off limits) Generally, slack-off weight becomes a limiting factor: for directional drilling when slide drilling is no longer possible for casing running when the casing will not slide into the hole due to the length and

angle of the hole Other Issues: when slack-off weight reaches zero for drilling and casing operations, we call these

wells negative weight wells pick-up drag is generally only an issue for casing and/or completion operations or for

ER wells with long vertical sections at TD Many of the casing strings that are run in extended reach wells are too long, and

therefore too heavy to pull from the hole. These runs become one way trips and require a very clean hole to be successful

Drag generally becomes a limiting factor for running casing and completions before it begins to hinder the drilling and tripping processes.

BUCKLING Buckling of drillpipe and casing results from excessive compression loads that build up in the string due to axial friction. Drill string and completion string buckling is a common problem in ERD wells. As the length of high angle hole sections become longer, unconstrained pipe will begin to bend in the wellbore. As this becomes more severe, a helix will develop and eventually prevent the pipe from running into the hole. Operations that are most prone to buckling are: slide drilling running liners running completions that require some stab-in weight




HOLE CLEANING

A thorough understanding of the dynamics behind good hole cleaning is critical to the success of ERD wells. For high angle wells, in general, cuttings will fall to the low side of the hole and away from the primary fluid flow at the top of the hole. This makes removing the cuttings from the hole difficult and requires special techniques for various well inclinations. The drilling parameters, BHA and bit designs, mud rheology and hole condition will all have a significant effect on the rig systems ability to effectively clean the hole. To ensure good hole cleaning, it is critical that flowrates and pipe RPM are maintained at high levels throughout the drilling process. It is important to note that hole cleaning practices used to clean vertical or low angle wells, will not be successful in high angle ERD wells.

ECDS ER wells inherently have higher ECD (Equivalent Circulating Density) fluctuations than conventional wells. With the advent of MWD based Pressure While Drilling (PWD) technology, the industrys understanding of ECDs has been seriously challenged. It has been observed that the magnitude of ECD fluctuations is far greater than previously thought. ECDs are more serious in ERD wells because: the magnitudes of the fluctuations are worse due to longer MD relative to TVD and

the drilling parameters must usually be more aggressive to maintain hole cleaning, while the mud system can allow less scope for compromise

wellbore stability, lost circulation and other key effects are generally more severe and less tolerable in these wells

temperature and pressure variations (and their effect on mud properties) are also more extreme in these wells.

POWER REQUIREMENT

The combined power usage when deep on a long ERD well may become an issue. It is often at this point, that maximum output levels are required from the mud pump, drawworks and the rotary system. Many of the industrys rigs that are being utilized for ERD drilling do not have the capability to meet the combined output requirements. Backreaming is the most taxing operation when considering the combined output issue. If good hole condition and hole cleaning practices are utilized, then backreaming can be discounted from the design plan. Although this may seem a bit haphazard at first glance, it is now a common consideration in many K&M client wells.




SURVEY ACCURACY

AND TARGET DEFINITION

Survey accuracy is often a critical aspect of ERD wells that is either discounted altogether, or widely misunderstood. ERD wells make survey accuracy more critical because: increased MD results in increased cumulative survey error the target size is effectively reduced at high angle (see Figure 46) survey tool accuracy can deteriorate markedly at high angle (especially if in an east-

west direction at high latitudes) the ability to change direction to get back into the target is usually more limited Target definition is the size, shape and logic behind the target area. The manner in which the target is defined has a direct effect on the well time and cost, as well as the required directional drilling strategies. The angle of attack (how the target looks from the bit) coming into the target plays a big role in the difficulty of hitting the target. It must be remembered that at 60 - 80 angle, the shape and size of the target area is markedly different than it appears on a plan-view map. The surveying uncertainty combined with the effective target area and the directional drilling strategy drives the surveying strategy for ERD wells.

WELLBORE INSTABILITY / DIFFERENTIAL

STICKING / STUCK PIPE

Wellbore instability is usually more critical on ERD wells due to: the increased wellbore angle increased hole exposure time increased ECD fluctuations and effects increased importance of good hole for acceptable hole cleaning at high angle. Differential sticking is also often more common in these wells as: mud weight is often higher on ERD wells (for wellbore stability at high angles) the exposed reservoir intervals are longer in length the exposed reservoir intervals are open for a longer time the drillstring and BHA will be on the low side of the hole and at least partially

buried in cuttings throughout the reservoir section. Differential sticking is even more important for wells where torque, drag or buckling problems exist, since even minor differential sticking increases friction considerably. Furthermore, the ability to jar or work the pipe free is reduced on ERD wells. Because of the reduced ability to get weight or tension down to the BHA, operational tolerances leading to stuck pipe are greatly reduced. For example, in a conventional well, up to 100-150 kips of overpull may result in permanently stuck pipe, whereas in an ERD well the BHA may be permanently stuck with as little as 20-50 kips of overpull. In wells with significant drag, it may not be possible to cock the jars.




CASING WEAR In general, casing wear is not a major concern in ERD wells due to much lower pipe tension across the build section of the well. However, in some cases with poor practices and inappropriate equipment, casing wear can be more of a risk on ERD wells. The following are the key factors for minimizing the chances of casing wear: a smooth build section the use of good quality drillpipe hardbanding elimination of backreaming If casing wear is managed effectively, high rotary speeds and thin walled casing can be used safely despite long drilling periods through this casing. As an example, BP at Wytch Farm successfully used light weight 9 40 ppf casing (instead of the usual 47 ppf casing). Despite drilling 8 hole for up to 60-80 days at depths up to 10000m (33000), BP has not experienced significant casing wear problems.

RIG CAPABILITY

ER wells challenge a rigs capabilities more readily than a conventional directional well of the same measured depth (except for pick-up loads). The need to use higher flowrates continuously at higher pressures, use of higher pipe RPM and higher torque and drag forces will begin to tax a rigs output capability and preventative maintenance program. Also, power may be limited, especially in a backreaming scenario (where pick-up, torque and pumps are all working hard). It is important to understand that embarking on an ERD program which places continuous high loads on the rig systems will result in increased rig downtime. Changing the preventative maintenance strategies to account for this fact has proven to be cost effective for the Operator. For instance, paying to change out all of the expendable pump parts at the beginning of a critical hole section, even though the parts may not have significant hours on them, will pay dividends in reduced downtime during critical sections of the well. Not only do these increased loads increase well time and risk, but the need to drill smarter, as described herein, becomes paramount. ER wells commonly drill with much of the drill string in compression. Oil field tubulars are not designed to drill in compression, but the gravity holding the pipe to the low side of the hole prevents catastrophic problems from occurring. Nonetheless, over time, this environment does stress and degrade drilling tubulars leading to failures that are more frequent. Fishing operations in ERD wells also present unique challenges, which must be addressed in the design stages of the well to ensure that proper tools are available when they are required.




WELL CONTROL

Well control is generally more challenging in an ERD environment. Kicks are often more difficult to detect and measure in high angle wells due to: Simple geometry - where the shut-in pressure impact of a swabbed influx is much

less due to the high angle where the influx occurred. For example, a gas kick in vertical wellbore may contribute 300 TVD length of bubble, whereas it will have only 30 TVD height in an 85 wellbore, and zero effect in a horizontal wellbore.

OBM or SBM drilling fluids are often necessary for lubricity and other reasons. Gas solubility and mud compressibility factors (combined with large annular mud volumes) can mask influx detection.

Not only is detecting a kick often more difficult, but the ability to manage and kill the well control problem is more difficult due to: The flow mechanics in a shut-in wellbore at high angle prevents the kill mud from

fully displacing the hole. The kill mud will be pumped up the high side of the hole and cannot completely displace out the stagnant lightweight mud in the low side, due to lack of pipe rotation.

The mud volumes and barite quantities are huge for large ERD wells, and so even the smallest of kicks will require some waiting period while additional mud and barite is delivered. It is not unusual for several kill attempts to be necessary in these wells, even if the correct kill weight mud was used in the first attempt.

Furthermore, the risk of swabbing a kick in an ERD well is increased due to: The presence of a static cuttings bed reduces the flow-by area around the bit The bit selection and stabilizer designs typically used in ERD (say for improved

steerability performance) mean reduced junk-slot area. Because of ECD and pump pressure reasons, mud weights are typically run as low as

practicable on ERD wells, reducing the static overbalance pressure. The trip distances are much greater (and often more trips are made), and so the

opportunities for swabbing are increased. Rig crews and supervisory personnel must be familiar with the need to use deviated kill-sheets since vertical-kill sheets are no longer applicable in high angle wellbores.




LOGISTICS Logistics are far more complex and more difficult to manage in ERD. Unless the offshore Drilling Supervisor is given additional logistics management support, he/she will be overwhelmed by the logistics management issues (or at least be completely devoted to it). Examples of scenarios that require heightened logistics management: OBM/SBM transfers:

- Building / delivering initial mud volumes, - Running casing (especially if casing is run empty), where large mud volumes may

be recovered and must then be (a) stored or sent away, or (b) stored and pumped down hole for the cement job or casing fill-up.

Well control (large mud volumes and barite quantities) Drillpipe racking space in the derrick is often insufficient for long ERD wells,

especially if tapered or multiple drillstrings are necessary. If inverted drillstrings are necessary to manage drag and buckling, then this is made even more difficult again. It is not uncommon for the last portion of an ERD well to require that drillpipe is picked-up/laid-down due to insufficient derrick capacity, or to make room on the floor to run casing.

Substructure weight limitations may prevent the combination of a full derrick of drillpipe and casing on the pipe rack. This may be further complicated if mud storage capacity on board must be increased to manage OBM/SBM usage.

For ultra-long ERD wells, there is often inadequate space available to store casing on the pipe rack and some casing may need to be run off of the boats. Casing stacked very high can create safety and storage problems.

Accommodation for personnel is often a key issue for ERD wells. Additional personnel are almost always required for these wells (such as for SBM mud systems, extra solids control equipment, different directional drilling tools, extra rig crews for running casing, etc.).

TIME AND COST

The very nature of ERD wells with their more critical build sections; higher tangent angles and deeper depths make them more difficult than conventional wells. As such, many of the cost related short cuts that can be used in conventional wells should be carefully reconsidered before they are used on ERD wells. Although the use of any proven premium technology should still be justified on a well-by-well basis, it is accurate to state that better quality equipment and materials are usually cost effective on ERD wells. When things go wrong on ERD wells, recovery time is also greatly increased and time and cost estimates need to consider this increased exposure.




HSE ISSUES ER wells are exposed to higher HSE risks in several areas: The stress levels on equipment will be significantly higher than for conventional

ERD wells. There is a risk of boredom and tiredness during the long tripping operations Congestion on the platform due to the large volumes of fluids and equipment and

simultaneous handling (multiple cranes / forklifts) may lead to dangerous situations High fluid temperatures may occur Well control difficulties as discussed previously The stress on personnel is expected to be higher than during a normal drilling

operation (i.e. a failed log or bit may require several days round tripping) Drilling a relief well in the event of a blowout may not be successful initially due to

the large survey inaccuracy seen on an ERD well. Repeated intersection attempts may be necessary.

WELL PLANNING

Many of todays Operators are faced with higher workloads for an even less experienced staff. This is driving the use of yesterdays drilling programs on a, more or less, cut and paste basis. This is always accepted as a poor practice (driven by necessity), but it must be avoided at all cost on ERD programs. It is K&Ms experience that ERD wells should be designed from scratch as fit-for-purpose within the design constraints, rather than simply using a combination of standard tools and methods that are readily available. The term fit for purpose is often used in the drilling industry, however, due to the factors mentioned above, there is often tremendous scope for optimization. If applied properly, this optimization requires detailed planning and analysis, on a project as well as well-by-well basis. Planning needs to be supported by quality analysis of results and rig-time for engineers. It is unfortunate that in many cases, the off-the-shelf solution is utilized because the manpower is not available to do otherwise.



4.2 SPECIFIC SHALLOW ERD WELL DIFFERENCES Although their total measured depth may be relatively small when compared to the very long ERD wells, shallow type ERD wells do have significant issues that must be addressed. Some are common to all types of ERD wells, but others are specific to these long, shallow wellbores.

SHALLOW ERD WELL CHALLENGES

For very shallow ERD wells, relatively fast build rates are often required. Obtaining the required build rates in very shallow formations becomes critical to minimizing the final hole angle, and for minimizing effects of torque, drag and buckling later in the well. The final angle of the well is far more sensitive to the achievable build rate than for long ERD well types. Not only is very good directional control required, but build rates are often limited by the unconsolidated nature of shallow formations and stiffness of the large OD BHAs.

Shallow ERD wells typically must deal with negative weight issues and/or pipe buckling. This necessitates exotic casing running techniques, inverted drillstrings and often-large OD drillpipe to manage drillpipe buckling.

Casing running can also be affected by the faster build rates and soft, shallow formations inherent in this well type. It is not uncommon for this type of well to be sidetracked while running surface casing or while running into the hole with a stiff drilling assembly.

The shallow vertical depths and relatively long measured depths of these wells make equivalent circulating densities (ECDs) a significant issue. Drilling and casing/cementing ECDs often limit flowrates because of unconsolidated shallow sediments. This can be exacerbated on high stepout shallow wells by the need to use large OD drillpipe to overcome buckling problems. This is particularly important if cement integrity above the shoe for zonal isolation is required. The impending loss circulation problems will make this particularly challenging.



SHALLOW ERD WELL ADVANTAGES

The magnitude of forces and pressures are much less than for long ERD wells. Hence, smaller drilling rigs can be successfully utilized. With the smaller forces, less brute force will be required to overcome operational problems.

Although drag forces may be a problem for completion and workover operations, most workover rigs would be able to overcome these problems with their conventional equipment, again, due to the lower magnitude of these forces.

The shorter nature of the wells means that hole sections will be smaller and, therefore, hole exposure times will be less than for very long ERD wells. This will help to reduce effects such as formation hydration, etc.

4.3 SPECIFIC LONG ERD WELL DIFFERENCES When ERD wells start to become very long with very high tangent angles, the magnitudes of the forces encountered require significant pull, torque, power, flowrate and pressure capability. Often, even purpose built ERD rigs must be upgraded for successful and efficient drilling of todays mega wells.

LONG ERD WELL CHALLENGES

Torque and pick-up loads may exceed rig or drillpipe capability. This often requires that measures be taken to (a) minimize or (b) manage these high loads. This includes bigger/stronger rig equipment, using more lubricious drilling fluids, wellpath and casing set depth optimization, or use of specialized equipment.

Completions and workover options are limited, and may only be performed with the drilling rig. The completion may have to be designed specifically to allow workovers with available rigs in the area once the drilling equipment has left. In some cases, the completion may be unserviceable (either due to economics or feasibility).

Drilling rig equipment reliability is tested due to continuous high operating loads.

Survey uncertainty is increased due to the length and high angle of the wellpath.

Hole exposure time is increased compared to conventional wells. This effects wellbore instability and therefore, mud weight and type, differential sticking and well cost.



LONG ERD WELL CHALLENGES (CONT..)

ECDs can be difficult to manage in smaller hole sections near TD due to the long wellpath. This can be particularly important when cementing 7 liners or even when running long buoyancy assisted 9 casing strings.

Cementing can be very challenging for long ERD wells due to the long pump times and high angle nature of the wellbores involved (especially for long strings of 13 and 9 casing). Obtaining a good primary cement job is made even more significant for ERD wells given the extremely high cost and limited capability to perform remedial cement jobs. The ability to obtain a good primary cement job is governed by: the ability to maintain the integrity of the cement into the annulus in the same form as it left the

surface the ability to move the pipe during the cement job and, therefore, to obtain good annular

displacement of the pre-flushes and cement the ability to obtain a properly designed cementing program that will remove the filter-cake buildup

on the low side of the hole and then obtain the required zonal isolation.

Logistics management is often difficult and complex for such large wells.

4.4 SPECIFIC DEEP WATER ERD WELL DIFFERENCES Deepwater ERD wells have become more common in the last few years. These wells combine the already significant challenges of deepwater drilling, with specific ERD challenges. In most cases, specialized engineering solutions may be required to overcome the resulting challenges.

DEEPWATER ERD WELL CHALLENGES

ECDs are the primary limitation, even in big hole sections (i.e. 17 and 12). This is mainly due to reduced overburden strength with the deepwater section. Big hole sections are often limited by cuttings loading in the riser, which acts to limit effective ROP (which therefore restricts ability of directional driller to apply WOB).

Hole cleaning in long sections of large OD riser can be difficult. Often, extra pumping capacity (if available) is required to boost the riser. Hole cleaning within the riser is likely already limited by the need to use thinner fluids for ECD management.

Low temperatures in the riser result in significant changes in mud rheology. The main impact is on the ECDs as the mud thickens.



DEEPWATER ERD WELL CHALLENGES (CONT..)

As for the shallow ERD wells, relatively fast build rates are often required, but very difficult to obtain. Not only is very good directional control required, but build rates are often limited by the unconsolidated nature of shallow formations and stiffness of the large OD BHAs.

Buckling of the drillstring in the large OD riser is a concern when drilling and especially when running casing and liners. Unlike platform drilling, the casing strings are typically run on drillpipe, which will experience severe buckling if it has to push the casing into the high angle portion. This may require casing landing strings or flotation techniques to manage buckling.

Negative weight conditions (as opposed to buckling problems) are less likely, due to long vertical column that provides surface weight.

The cost environment is very expensive. This influences Operators toward solutions that place rig-time as the #1 priority.

Drilling rigs for deep-water tend to be fit-for-purpose and usually have significantly improved hydraulics and solids control packages. In general, ECDs will be a limit rather than surface-pressures, unless drilling at deep TVDs with heavy mud weights.

Pressure While Drilling (PWD) tools are more critical.

Further detail can be found in Section 16.



5 PLANNING ERD WELLS The following section presents a broad overview of the planning process for an ERD well. The key to planning is not to treat an ERD well as just another well in the program. Designs must be fit-for-purpose and specific to the well in question. Time spent planning upfront will definitely pay off in the operational phase in both performance improvements, and the avoidance of train-wrecks. K&M knows of many ERD wells that have been lost or made uneconomic by a lack of effective planning. Detailed planning is the key to ERD success!

5.1 ORGANIZATIONAL STRUCTURE You may challenge the applicability of a topic such as this in a technical manual. The fact is that with this industrys dynamic corporate environment, and the inherently long planning and implementation time associated with todays ERD programming, the maintenance of a consistent team to see the project through can be critical to its success. ER programs generally push rig systems and available technologies to their limits. For this reason, a core design team that includes all of the releva

k&m erd textbook, 3rd edition

Documents

general erd differences

erd definitions

planning erd wells

specific shallow erd

specific long erd

specific deep water

technology group

erd project planning