Processing and Modeling Deep-Water 2D4C OBC Seismic Data

194 Pages·2008·16.14 MB·English

Processing and Modeling
Deep-Water 2D4C OBC Seismic Data
Final Report
Reporting Period Start Date: 22 September 2005
Reporting Period End Date: 30 September 2007
Report Date: 31 January 2008
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MMS Contract: 1435-01-05-CT-39388
Principal Investigator: Bob A. Hardage

Submitting Organization:
Bureau of Economic Geology
The University of Texas at Austin
Austin, TX 78713-8924
January 2008
PROCESSING AND MODELING
DEEP-WATER 2D4C OBC
SEISMIC DATA

FINAL REPORT

Project Period Start Date: 22 September 2005

End of Project Funding: 30 September 2007

Report Date: 31 January 2008

MMS Contract No. 1435-01-05-CT-39388

Submitting Organization: Bureau of Economic Geology
The University of Texas at Austin
University Station, Box X
Austin, TX 78713-8924

Principal Investigator: Bob A. Hardage

This draft report has not been reviewed by the Minerals Management Service, nor has it been
approved for publication. Approval, when given, does not signify that the contents necessarily
reflect the views and policies of the Service, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
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Table of Contents

Chapter 1 – Interpretation of Hydrate Systems, Green Canyon Area,
Gulf of Mexico......................................................................................1

Introduction................................................................................................................1
Examples of Interpreted AUV P-P and OBC P-SV Images........................................2
Examples of Interpreted OBC P-P and P-SV Images..............................................10
Examples of Raytracing to Determine Layer Velocities...........................................16
Velocity Analysis at Calibration Wells......................................................................20
Integration of Resistivity, Velocity, and Seismic Data..............................................22
Joint Inversion of Resistivity and Velocity: Theory...................................................29
Joint Inversion of Resistivity and Velocity: Examples...............................................35
2D Profiles of Velocity Layering...............................................................................39
2D Profiles of Hydrate Concentration.......................................................................41
Mapping the Amount of In Situ Hydrate...................................................................43
Comparing Load-Bearing and Pore-Filling Hydrate Assumptions............................44
Conclusions.............................................................................................................46

Chapter 2 – Processing 4C OBC Seismic Data to Image Deep-Water,
Near-Seafloor Geology......................................................................48

Introduction..............................................................................................................48
Theoretical Concepts...............................................................................................49
P-P Trace Gathers...................................................................................................50
P-SV Trace Gathers.................................................................................................52
Calculating Reflectivity.............................................................................................54
Creating Local Common-Receiver Images..............................................................55
Creating Continuous Images along an OBC Profile.................................................57
Comparison with State-of-the-Art Imaging...............................................................60
Comparison with VSP Imaging................................................................................64
Receiver Calibration.................................................................................................64
Equalizing Hydrophone and Vertical-Geophone Data..............................................66
Equalizing Hydrophone and Horizontal-Geophone Data.........................................69
Calibrated vs. Uncalibrated Data.............................................................................70
Conclusions.............................................................................................................73

Chapter 3 – Rock Physics: Near-Seafloor, Deep-Water Sediments and
Seismic Velocities..............................................................................74

Introduction..............................................................................................................74
Rock Physics of Unconsolidated Sediments............................................................75
Hertz-Mindlin Theory................................................................................................76
Walton Model...........................................................................................................77
Methodology............................................................................................................78
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Rock Physics Models for Hydrate Systems .............................................................80
Model A: Hydrates as a Load-Bearing Component..................................................81
Model B: Hydrates as Pore-Filling Clathrates..........................................................83
Model C: Thin Layers of Pure Hydrate and Sediment..............................................84
Model D: Thin Layers of Disseminated Hydrate.......................................................85
Modeling Results.....................................................................................................86
Pure-Quartz Host Sediment.....................................................................................86
Mixed-Mineralogy Host Sediment............................................................................92
P-P and P-SV AVA Modeling: Base of Hydrate Stability Zone.................................96
Comparing Modeling Results with Laboratory Measurements...............................104
Conclusions...........................................................................................................106

Chapter 4 – Rock Physics: Resistivity Models for Deep-Water Hydrate
Systems and Well Log Examples...................................................109

Introduction............................................................................................................109
Resistivity Models of Sediment-Hydrate Systems..................................................109
Archie Equation......................................................................................................113
Hashin-Shtrikman Bounds.....................................................................................114
Hashin-Shtrikman Lower Bound............................................................................117
Laboratory Confirmation of Resistivity Behavior....................................................121
Well Log Database.................................................................................................122
Well Log Data: Typhoon Field Area.......................................................................124
Well Log Data: Genesis Field Area........................................................................132
Maps of Generalized Properties of Hydrate Systems............................................138
Well Log Data: Additional Green Canyon Lease Blocks........................................141
Conclusions...........................................................................................................146

Chapter 5 – Estimating Hydrate Concentrations from Resistivity Logs.........147

Introduction............................................................................................................147
Archie Equation Corrected for Clay........................................................................147
Motivation for Quantifying Uncertainty...................................................................152
Uncertainty in Estimating Hydrate Concentration...................................................153
Conclusions...........................................................................................................162

Chapter 6 – Project Database.............................................................................163

Introduction............................................................................................................163
Database Contribution 1: Seafloor Borings............................................................164
Porosity Profiles.....................................................................................................164
Porosity from Water-Content Data.........................................................................166
Porosity from Measurements of Submerged Unit Weight......................................168
Shear Modulus.......................................................................................................169
Vertical Effective Pressure.....................................................................................171
Database Contribution 2: AUV Data......................................................................172
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Database Contribution 3: Well Log Data................................................................174
Database Contribution 4: 4C OBC Seismic Data...................................................177
Conclusions...........................................................................................................178

References ...........................................................................................................179

Acronyms and Abbreviations.............................................................................183

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List of Figures

Chapter 1
Figure 1.1. OBC P-SV and AUV P-P images, Typhoon Field....................................4
Figure 1.2. OBC P-SV and AUV P-P images, Typhoon Field....................................6
Figure 1.3. OBC P-SV and AUV P-P images, Genesis Field.....................................8
Figure 1.4. OBC P-P and P-SV images, Typhoon Field...........................................11
Figure 1.5. OBC P-P and AUV P-P images, Genesis Field .....................................13
Figure 1.6. OBC P-P and P-SV images, Genesis Field...........................................14
Figure 1.7. Calculating sub-seafloor interval velocities............................................17
Figure 1.8. Example of sub-seafloor velocity model.................................................18
Figure 1.9. Accuracy of V interval velocities...........................................................19
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Figure 1.10. Accuracy of V interval velocities.........................................................20
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Figure 1.11. Velocity analysis, Well B, Genesis Field..............................................21
Figure 1.12. Velocity analysis, Well C, Genesis Field..............................................21
Figure 1.13. Velocity and seismic integration, Well C, Genesis Field......................23
Figure 1.14. Resistivity and seismic integration, Well C, Genesis Field...................25
Figure 1.15. Velocity and seismic integration, Well B, Genesis Field.......................27
Figure 1.16. Resistivity and seismic integration, Well B, Genesis Field...................28
Figure 1.17. Importance of joint inversion................................................................30
Figure 1.18. Depth dependence of inversion parameters........................................32
Figure 1.19. Joint inversion of resistivity and velocity data......................................33
Figure 1.20. Joint inversion for hydrate concentration, Well B, Genesis Field.........36
Figure 1.21. Joint inversion for hydrate concentration, Well A, Typhoon Field ........37
Figure 1.22. Joint inversion for hydrate concentration, Well 4 .................................38
Figure 1.23. 2D velocity layering, OBC profile 549, Genesis Field ..........................40
Figure 1.24. 2D velocity layering, OBC profile 553, Genesis Field ..........................41
Figure 1.25. 2D profiles of hydrate concentration, Genesis Field ............................42
Figure 1.26. Map of in situ hydrate across study area.............................................43
Figure 1.27. Comparison of hydrate concentration..................................................45

Chapter 2
Figure 2.1. Example of 4C OBC data.......................................................................49
Figure 2.2. Basic response equations for 4C OBC sensors.....................................50
Figure 2.3. Upgoing and downgoing P wavefields...................................................52
Figure 2.4. Upgoing PS wavefield............................................................................53
Figure 2.5. PP and PS reflectivities..........................................................................55
Figure 2.6. PP reflectivity with dynamic corrections.................................................56
Figure 2.7. PP reflectivity with overlay of image-trace corridors ..............................57
Figure 2.8. PS reflectivity with overlay of image-trace corridors ..............................58
Figure 2.9. Comparison of local-station and full-profile PP imaging.........................59
Figure 2.10. Comparison of local-station and full-profile PS imaging.......................60
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Figure 2.11. Comparison of EGL and contractor PP imaging..................................61
Figure 2.12. Comparison of EGL and contractor PS imaging..................................62
Figure 2.13. Comparison of AUV PP and OBC PS images.....................................63
Figure 2.14. Data windows used for sensor calibration............................................65
Figure 2.15. Early arrival events..............................................................................66
Figure 2.16. Example of early-arrival sensor calibration..........................................67
Figure 2.17. Sensor calibration operators................................................................68
Figure 2.18. P and Z sensor calibration...................................................................69
Figure 2.19. P and X sensor calibration...................................................................70
Figure 2.20. Images made with and without sensor calibration ...............................72

Chapter 3
Figure 3.1. Models of hydrate-sediment morphology...............................................82
Figure 3.2. V versus hydrate concentration, pure quartz host................................88
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Figure 3.3. V versus hydrate concentration, pure quartz host................................89
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Figure 3.4. V /V versus hydrate concentration, pure quartz host...........................91
P S
Figure 3.5. V as a function of hydrate and clay percentages..................................93
P
Figure 3.6. V as a function of hydrate and clay percentages..................................94
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Figure 3.7. V /V as a function of hydrate and clay percentages.............................95
P S
Figure 3.8. Earth layer model for BHSZ...................................................................96
Figure 3.9. AVA response at BHSZ for Model A, 80-percent free gas.....................97
Figure 3.10. AVA response at BHSZ for Model B, 80-percent free gas...................98
Figure 3.11. AVA response at BHSZ for Model A, 10-percent free gas...................99
Figure 3.12. AVA response at BHSZ for Model B, 10-percent free gas.................100
Figure 3.13. Model C converted to vertical-layer models.......................................101
Figure 3.14. Reflectivities at BHSZ, Model C, 5-percent free gas..........................102
Figure 3.15. Azimuth dependence of PP reflectivity, Model C...............................103
Figure 3.16. Reflectivities at BHSZ, Model C, no free gas.....................................104
Figure 3.17. Model A calculations of V and lab measurements............................105
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Figure 3.18. Model A calculations of V and lab measurements............................105
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Chapter 4
Figure 4.1. Resistivity model for disseminated hydrate..........................................110
Figure 4.2. Resistivity models for layered hydrate.................................................111
Figure 4.3. Photo of polygonal fractures................................................................112
Figure 4.4. 3D seismic images of polygonal faults.................................................113
Figure 4.5. Hashin-Shtrikman upper and lower bounds.........................................116
Figure 4.6. Crossplot of porosity and normalized resistivity...................................118
Figure 4.7. Hashin-Shtrikman calibration of Archie equation.................................119
Figure 4.8. Electrical conductivity lab measurements............................................122
Figure 4.9. Calibration wells across Typhoon Field area .......................................123
Figure 4.10. Rejected calibration wells, Typhoon Field area..................................125
Figure 4.11. Well log section BCA, Typhoon Field area.........................................126
Figure 4.12. Well log section BDE, Typhoon Field area.........................................127
Figure 4.13. Thickness of hydrate stability zone....................................................128
Figure 4.14. Examples of hydrate zones, Typhoon Field area...............................129
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Figure 4.15. Calibration wells, Genesis Field area.................................................130
Figure 4.16. Rejected calibration wells, Genesis Field area ..................................131
Figure 4.17 Well log section ABC, Genesis Field area..........................................133
Figure 4.18. Well log section DEFG, Genesis Field area.......................................134
Figure 4.19. Well log section HILJ, Genesis Field area.........................................135
Figure 4.20. Examples of hydrate zones, Genesis field.........................................136
Figure 4.21. Examples of hydrate zones, Brutus Field...........................................137
Figure 4.22. Examples of hydrate zones, Genesis Field........................................138
Figure 4.23. Hydrate domains, Typhoon Field area...............................................140
Figure 4.24. Hydrate domains, Genesis Field area................................................141
Figure 4.25. Calibration wells remote from Typhoon and Genesis Fields..............142
Figure 4.26. Well log section 1,2,3.........................................................................143
Figure 4.27. Well log section 5,4,7.........................................................................144
Figure 4.28. Well log section 8,9,10.......................................................................145

Chapter 5
Figure 5.1. Prediction error dependence on m ......................................................150
Figure 5.2. Prediction error dependence on R (low values)...................................151
Figure 5.3. Prediction error dependence on R (high values)..................................151
Figure 5.4. Hydrate prediction for high R values....................................................152
Figure 5.5. Distribution functions for Archie equation parameters .........................155
Figure 5.6. Distribution function for log reading .....................................................155
Figure 5.7. Hydrate concentration calculated for well W1......................................156
Figure 5.8. Hydrate concentration calculated for well W2......................................157
Figure 5.9. Hydrate concentration calculated for well W3......................................157
Figure 5.10. Hydrate concentration calculated for well W4....................................158
Figure 5.11. Hydrate concentration calculated for well W5....................................158
Figure 5.12. Depth-based hydrate concentration, well W1....................................159
Figure 5.13. Depth-based hydrate concentration, well W2....................................160
Figure 5.14. Depth-based hydrate concentration, well W3....................................160
Figure 5.15. Depth-based hydrate concentration, well W4....................................161
Figure 5.16. Depth-based hydrate concentration, well W5....................................161

Chapter 6
Figure 6.1. Location of AUV profiles......................................................................165
Figure 6.2. Location of 4C OBC profiles................................................................166
Figure 6.3. Use of water-content lab data..............................................................167
Figure 6.4. Use of submerged-unit-weight lab data...............................................169
Figure 6.5. Lab measured shear-strength data......................................................170
Figure 6.6. Vertical effective pressure....................................................................172
Figure 6.7. AUV system concept ...........................................................................173
Figure 6.8. AUV chirp-sonar profile........................................................................174
Figure 6.9. 4C OBC survey areas..........................................................................176
Figure 6.10. Key calibration wells, Area 3..............................................................177

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Tables

Table 6.1. Itemized research database..................................................................175

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