NMR Logging Principles and Applications

Transcription

1 NMR Logging Principles and Applications George R. Coates, Lizhi Xiao, and Manfred G. Prammer Halliburton Energy Services Houston iii

2 Halliburton Energy Services Contents Foreword xi Preface xiii Editors and Editorial Review Board xv Acknowledgments xvii Chapter 1 Summary of NMR Logging Applications and Benefits 1 Medical MRI 1 MRI Logging 2 Comparison of the MRIL Tool to Other Logging Tools 2 Fluid Quantity 3 Fluid Properties 4 Pore Size and Porosity 4 NMR-Logging Raw Data 6 NMR Porosity 7 NMR T 2 Distribution 7 NMR Free-Fluid Index and Bulk Volume Irreducible 8 NMR Permeability 9 NMR Properties of Reservoir Fluids 11 NMR Hydrocarbon Typing 11 NMR Enhanced Water Saturation with Resistivity Data 16 MRIL Application Examples 16 MRIL Porosity and Permeability 16 Low-Resistivity Reservoir Evaluation 22 MRIL Acquisition Data Sets 25 MRIL Response in Rugose Holes 26 NMR Logging Applications Summary 26 References 28 Chapter 2 NMR Physics 33 Nuclear Magnetism 33 Polarization 34 Pulse Tipping and Free Induction Decay 37 Spin-Echo Detection 39 Table of Contents v

3 NMR Logging Principles and Applications NMR-Measurement Timing 42 References 43 Chapter 3 Fundamentals of NMR Petrophysics 45 NMR Relaxation Mechanisms of Fluids in Rock Pores 45 Bulk Relaxation 47 Surface Relaxation 48 Diffusion-Induced Relaxation 48 Multi-Exponential Decay 51 Echo-Fit for T 2 Distribution 53 Pore Size Distribution 54 Determination of BVI 57 Cutoff BVI 57 Spectral BVI 60 MRIL Permeability Model 64 The Free Fluid Model 64 The Mean T 2 Model 65 MRIL Porosity Model 65 References 67 Chapter 4 Fundamentals of NMR Hydrocarbon Typing 77 NMR Properties of Hydrocarbons 77 NMR Hydrocarbon Typing 80 T 2 Distribution of a Partially Saturated Rock 80 T 1 Relaxation Contrast 80 Diffusivity Contrast 82 Numerical Simulations 83 Oil Effects on T 2 Distributions 84 Water and Light Oil 84 Water and Viscous Oil 85 Effects of Viscosity and Wettability on the Oil Signal in a T 2 Distribution 85 Gas Effects on T 2 Distribution Under Different Conditions 87 Water and Gas 88 Water, Light Oil, and Gas 89 References 89 Chapter 5 MRIL Tool Principles 91 Polarization 91 Magnetization Tipping and Spin-Echo Detection 91 Logging Speed and Vertical Resolution 94 Depth of Investigation 96 Multi-Frequency Measurement and RF Pulse Bandwidth 98 Ringing Effect 102 Signal-to-Noise Ratio and Running Average 104 Activations 104 Tool Configuration 108 References 108 vi Table of Contents

4 Halliburton Energy Services Chapter 6 Answer Products Derived from MRIL Stand-Alone Analysis 113 Time Domain Analysis 113 Concept 113 Principle 113 Differential Spectrum Method 113 Time Domain Analysis 114 Data Acquisition 114 Applications 116 Example Example Example Diffusion Analysis 122 Concept 122 Data Acquisition 123 Shifted Spectrum Method 124 Quantitative Diffusion Analysis: DIFAN 124 Enhanced Diffusion Method 127 Appendix: TDA Mathematical Model 129 References 133 Chapter 7 Answer Products Derived from MRIL Combinations with Other Logs 135 MRIAN Concept 135 MRIAN Principles 135 Dual-Water Model 135 Determining S wb for the Dual-Water Model 137 Quality Control on the Calculated S wb 137 Determination of the W Exponent in MRIAN 138 Calculation of S wt in MRIAN 139 Parameters Affecting MRIAN Calculations 139 MRIL Data Acquisition for MRIAN 139 MRIAN Applications 142 Low-Resistivity Reservoir Low-Resistivity Reservoir Gas-Influx Monitoring with MRIL in an Arabian Gulf Carbonate 146 Evaluation of a Shaly, Tuff Sandstone Formation Containing Medium-Viscosity Oils 147 MRIAN in a Light-Hydrocarbon Well 150 Well Completion with MRIL: StiMRIL 150 References 154 Chapter 8 MRIL Job Planning 159 Determining NMR Properties of Reservoir Fluids 160 Example 1: OBM, Gas 161 Well Description 161 Example 1, Step 1: Determine NMR Fluid Properties 161 Assessing the Expected Decay Spectrum of Reservoir Fluids in a Formation 162 Example 1, Step 2a: Assess Expected NMR Response (T 2 Distribution) 163 Assessing the Expected NMR Apparent Porosity of a Formation 164 Table of Contents vii

5 NMR Logging Principles and Applications Example 1, Step 2b: Assess Expected NMR Response (Apparent Porosity) 165 Selection of the Activation Set 166 Standard T 2 Activation 166 Dual-TW Activation 167 Dual-TE Activation 167 Determination of the Activation Set and Acquisition Parameters 167 Standard T 2 Activations 168 Example 1, Step 3: Determine Appropriate Activation Parameters (TW, TE, NE) for a Standard T 2 Activation 168 Dual-TW Activations 169 Example 1, Step 3: Determine Appropriate Activation Parameters (TW L, TW S, TE, NE) for a Dual-TW Activation 170 Example 2: OBM Dual TW 172 Dual-TE Activations 174 Example 3: WBM, Viscous Oil, Dual TE 174 Well Description 174 Step 1: Determine NMR Fluid Properties 175 Step 2: Assess Expected NMR Response 175 Step 3: Determine Appropriate Activation Parameters (TE L, TE S, TW, and NE) for a Dual-TE Activation 175 Dual-TW/Dual-TE (Virgin Area Logging) 177 Step 1: Determine NMR Fluid Properties 177 Step 2: Assess Expected NMR Response 177 Step 3: Determine Appropriate Activation Parameters (TW L, TW S, TE L, TE S, NE L, and NE) 177 Example 4: OBM, Gas, Dual TW, TE 178 Well Description 178 Step 1: Determine NMR Fluid Properties 178 Step 2: Assess Expected NMR Response 179 Step 3: Determine Appropriate Activation Parameters (TW i, TE i, NE i ) 180 Other Considerations for MRIL Job Planning 181 Formation Type (Sandstone, Carbonate, Chalk, Diatomite) 181 Wettability 181 Mud Type (Oil-Based, Water-Based) 182 Trade Off Logging Speed Accuracy (S/N, Sampling Rate) Type and Detail of Information 183 References 184 Chapter 9 MRIL Log Quality Control 185 Concepts and Definitions 185 Gain and Q Level 185 B 1 and B 1mod 186 Chi 186 Noise Indicators: OFFSET, NOISE, RINGING, and IENoise 186 Low-Voltage Sensors 187 High-Voltage Sensors 187 Phase Correction Information: PHER, PHNO, and PHCO 188 Temperature 189 Pre-Logging Calibration and Verification 193 Calibration Procedure 194 Frequency Sweep 194 viii Table of Contents

6 Halliburton Energy Services Master Calibration 194 Tank Statistical Check 196 Electronics Verification 197 Quality Control During Logging 199 Operating Frequency 199 Logging Speed and Running Average 199 B 1 Adjustment for Downhole Conditions 201 Quality Monitoring During Data Acquisition 201 Log-Quality Display 202 Post-Logging Quality Check 206 MPHI Relation to MSIG on Total-Porosity Logs 206 MPHI TW S Relation to MPHI TW L on Dual-TW Logs 206 MPHI TE S Relation to MPHI TE L on Dual-TE Logs 206 Agreement between MPHI and Neutron-Density Crossplot Porosity 207 Effects of Hydrogen Index and Polarization Time on MPHI 207 Reference 207 Glossary 209 Index 227 Table of Contents ix

7 Foreword Halliburton Energy Services is pleased to contribute this important technical volume on Nuclear Magnetic Resonance Logging to the petroleum industry. The NMR logging represents a new revolution in formation evaluation with wireline logging, and this book gives a comprehensive treatment of this new technology. Since its acquisition of NUMAR in 1997, Halliburton has focused on advancing NMR techniques, and on integrating conventional log data with the NMR interpretation methodology to further enhance the NMR applications. To this end, a new NMR tool has been introduced, new data processing techniques have been developed, and new data interpretation packages (such as our real-time NMR answer product) have been made available to the industry. Besides explaining basic NMR principles and applications, this book provides an understanding of these latest achievements in NMR logging. This book was developed by three of our finest NMR experts in Halliburton and was reviewed by many recognized experts from our organization, from clients organizations, and from other institutions. I am particularly grateful for the dedication of the authors, Mr. George R. Coates, Director of Reservoir Applications at the Halliburton Houston Technology Center, Dr. Lizhi Xiao, Senior Research Scientist and Project Manager for this book, Dr. Manfred G. Prammer, President of NUMAR, and to the editors, Dr. Richard F. Sigal and Mr. Stephen J. Bollich. As the largest oilfield service company in the world, Halliburton is committed to providing services of the highest quality and best value, not only through field delivery but also through an understanding of underlying technology. This book is an example of this commitment, and I trust that you will find it useful in learning how NMR services can be of benefit in your applications. Dick Cheney CEO of Halliburton Company xi

8 Preface Well logging, the economic method of choice for evaluating drilled formations, has progressively improved its determination of porosity and fractional fluid saturation, but could not provide a systematic estimate of permeability. This shortcoming was why Nuclear Magnetic Resonance captured the interest of the petroleum industry when researchers published results showing a good permeability correlation in the 1960 s. Unfortunately this industry interest was left waiting for nearly 30 years on a reliable downhole measurement of NMR relaxation. In 1992, when NUMAR introduced its MRIL logging service this wait was over; and it was soon demonstrated that the long hoped for permeability determination could be systematically provided, especially in shaly sand formations. However, permeability was not the only petrophysical benefit provided by this new pulseecho NMR log. Many other petrophysical parameters mineral-independent total porosity; water, gas, and oil saturation independent of other logs; oil viscosity all have been found achievable. Several other parameters appear within reach, thus ensuring that this new uniform gradient NMR logging measurement will prove to be the richest single source of formation petrophysics yet devised by the well logging industry. This book has been prepared as a means of sharing these very exciting developments and to support those of you who are interested in formation evaluation technology. George R. Coates Director Reservoir Applications, Halliburton Energy Services xiii

9 Editors Richard F. Sigal and Stephen J. Bollich Editorial Review Board Internal Members Prabhakar Aadireddy Ron Cherry Gary J. Frisch Stefan Menger Ronnel C. Balliet Peter I. Day James E. Galford Daniel L. Miller Ron J. M. Bonnie Bob Engelman John S. Gardner Moustafa E. Oraby James Buchanan Maged Fam Dave Marschall Nick Wheeler External Members Ridvan Akkurt J. Justin Freeman George J. Hirasaki James D. Klein Robert J. S. Brown David C. Herrick Jasper A. Jackson xv

10 Acknowledgments In addition to our appreciation for the contributions of the editors and editorial review board, we wish to acknowledge and thank those who have helped so much with this book: Jennifer Wood reprocessed most of the MRIL data for the examples in the book. Karen J. Campbell prepared many of the plots and figures. Sandra Moynihan and Communication Services coordinated the final product process. Jorge Velasco, Ramsin Y. Eyvazzadeh, Fernando Salazar, Greg Strasser, and Jim Witkowsky provided most of the NMR logging data and support. Charley Siess, MRIL Product Manager, provided encouragement and support. Peter O'Shea, Tim Epresi, and Halliburton Resevoir Applications colleagues, provided help and support. Many thanks to the oil companies for release of their data for this publication. Finally, thanks to Metamor Documentation Solutions, Duncan, Oklahoma, for their role in preparing the book for publication. The Authors Houston, Texas September 18, 1999 xvii