Technical Addendum to the Winningsplan Groningen 2013 Subsidence, Induced Earthquakes and ...

243 Pages·2013·20.16 MB·English

Technical Addendum to the
Winningsplan Groningen 2013
Subsidence, Induced Earthquakes and
Seismic Hazard Analysis in the Groningen
Field

Date: November 2013

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Contents
0 Executive Summary ................................................................................................................................... 10
0.1 Background ................................................................................................................................. 10
0.2 Introduction ................................................................................................................................. 10
0.3 Historical Seismicity in the Groningen field ..................................................................................... 10
0.4 Results of Seismological Studies based on the historical seismic record .............................................. 11
0.5 Assessment of the Hazard ............................................................................................................. 11
0.6 Uncertainty in the Hazard Assessment ............................................................................................ 11
0.7 Alternative Production Strategies ................................................................................................... 12
0.7.1 Depletion .................................................................................................................................... 12
0.7.2 Pressure Maintenance .................................................................................................................. 13
0.8 Hazard Analysis of Alternative Production Strategies ....................................................................... 14
0.9 Results of Geomechanical Studies .................................................................................................. 14
0.10 Studies Programme ...................................................................................................................... 15
0.11 Independent Review ..................................................................................................................... 17
0.12 Independent review of ‘Report to the Technical Guidance Committee (TBO) on Subsurface Aspects
of Induced Earthquakes in the Groningen Field’ (part 1) .................................................................. 17
0.13 Independent review of ‘Report to the Technical Guidance Committee (TBO) on alternative
production measures and hazard analysis’ (part 2) ......................................................................... 18
1 Introduction .............................................................................................................................................. 21
2 Introduction to the Geology and Seismicity in the Groningen field .................................................................. 23
2.1 Regional Geology and Conceptual Structural Model ........................................................................ 23
2.1.1 Structural setting .......................................................................................................................... 23
2.1.2 Stratigraphy and depositional setting ............................................................................................. 25
2.1.3 Reservoir model and rock properties .............................................................................................. 27
2.2 Current Monitoring Network and Historical Seismicity in the Groningen Field .................................... 29
2.2.1 Previous Work ............................................................................................................................. 29
2.2.2 Seismic Monitoring Network ......................................................................................................... 29
2.3 Earthquake Statistics..................................................................................................................... 30
2.4 Compaction and Seismicity ........................................................................................................... 32
2.5 References ................................................................................................................................... 34
3 Gas production from the Groningen field..................................................................................................... 35
3.1 Historical production .................................................................................................................... 35
3.2 Pressure development in the field over time ..................................................................................... 37
3.3 Development projects ................................................................................................................... 39
3.3.1 Compression ............................................................................................................................... 39
3.3.2 New development wells ................................................................................................................ 39
3.3.3 Development of the North-Western periphery ................................................................................. 40
3.3.4 Development of the South-Western periphery ................................................................................. 40
3.3.5 Development of gas from the Carboniferous below the Groningen field ............................................. 41
3.4 Depletion of the Groningen Field ................................................................................................... 41
3.4.1 Depletion behaviour under the current production philosophy .......................................................... 41
3.4.2 Depletion behaviour under an alternative production philosophy ...................................................... 43
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3.4.3 Effect of subsurface uncertainty on depletion behaviour ................................................................... 46
3.5 Pressure Maintenance .................................................................................................................. 48
3.6 Scenarios .................................................................................................................................... 48
3.7 Conclusion .................................................................................................................................. 51
4 Historical compaction / subsidence and future trends ................................................................................... 52
4.1 Summary .................................................................................................................................... 52
4.2 Introduction ................................................................................................................................. 52
4.3 Geodetic and geomechanical data ................................................................................................ 52
4.3.1 Survey protocol............................................................................................................................ 52
4.3.2 Surveying techniques .................................................................................................................... 53
4.3.3 Survey design .............................................................................................................................. 54
4.3.4 Levelling and Insar data used for the calibration ............................................................................. 55
4.3.5 Data from uniaxial compaction experiments ................................................................................... 56
4.4 The Groningen Geomechanical model ........................................................................................... 58
4.4.1 Linear and Bi-linear Compaction Models ........................................................................................ 60
4.4.2 Time Decay Compaction Model ..................................................................................................... 62
4.4.3 Linear Isotach Compaction model .................................................................................................. 63
4.4.4 Upscaling of input data ................................................................................................................ 64
4.5 Comparing the finite element model with Geertsma and van Opstal, the possible influence of rock
salt creep .................................................................................................................................... 65
4.5.1 Zechstein salt creep ...................................................................................................................... 65
4.6 Calibration of the model ............................................................................................................... 69
4.6.1 RMS of all benchmarks using epoch combinations ........................................................................... 69
4.6.2 Basecase model ........................................................................................................................... 70
4.6.3 Results for the Bi-linear model ....................................................................................................... 71
4.6.4 Time decay.................................................................................................................................. 73
4.6.5 Isotach model .............................................................................................................................. 75
4.6.6 Comparison ................................................................................................................................ 78
4.6.7 Conclusion .................................................................................................................................. 79
4.7 Subsidence forecasts .................................................................................................................... 79
4.8 References ................................................................................................................................... 82
5 Illustrative examples of induced seismicity from other locations ....................................................................... 84
5.1 Introduction ................................................................................................................................. 84
5.1.1 Gazli .......................................................................................................................................... 84
5.1.2 Lorca .......................................................................................................................................... 85
5.1.3 Rotenburg ................................................................................................................................... 85
5.1.4 Lacq ........................................................................................................................................... 85
5.1.5 Yibal .......................................................................................................................................... 85
5.1.6 Ekofisk ........................................................................................................................................ 85
5.1.7 Fashing ....................................................................................................................................... 85
5.1.8 Other hydrocarbon fields in the Netherlands .................................................................................. 85
5.2 Concluding remarks ..................................................................................................................... 86
5.3 References ................................................................................................................................... 86
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5.4 Tables ......................................................................................................................................... 87
6 Release of energy by Earthquakes ............................................................................................................... 89
6.1 Analysis of the induced earthquake record ..................................................................................... 89
6.1.1 Frequency-magnitude distribution .................................................................................................. 89
6.1.2 Physical limits on the maximum magnitude ..................................................................................... 92
6.1.3 Finite strain limit .......................................................................................................................... 92
6.1.4 Finite fault size limit ...................................................................................................................... 92
6.1.5 Finite mass limit ........................................................................................................................... 93
6.2 The earthquake strain model ......................................................................................................... 93
6.2.1 Stress, compaction, faults and earthquakes ..................................................................................... 94
6.2.2 Earthquakes and gas production ................................................................................................... 96
6.2.3 Earthquakes and compaction ........................................................................................................ 98
6.2.4 Seismological model .................................................................................................................... 99
6.3 Potential influence of Time-Dependent and Rate-dependent Effects on future Seismicity ..................... 101
6.3.1 Time-dependent effects ............................................................................................................... 102
6.3.2 Rate-dependent effects ................................................................................................................ 102
6.4 Conclusions ............................................................................................................................... 103
6.5 Recommendations for further work............................................................................................... 103
6.6 References ................................................................................................................................. 104
7 Movement at surface ............................................................................................................................... 106
7.1 Ground-Motion Prediction Equations (GMPEs) .............................................................................. 106
7.2 Development of GMPEs for Groningen ......................................................................................... 108
7.2.1 Criteria for Groningen GMPEs .................................................................................................... 108
7.2.2 The Groningen Ground-Motion Database .................................................................................... 109
7.2.3 Selection and Modification of the Akkar et al. (2013) GMPE .......................................................... 112
7.2.4 Epistemic Uncertainty in Ground-Motion Predictions ...................................................................... 114
7.2.5 Spatial Correlations in Ground Motions ....................................................................................... 114
7.2.6 Duration of Ground Shaking ....................................................................................................... 115
7.3 Conclusions ............................................................................................................................... 115
7.4 References ................................................................................................................................. 116
8 Probabilistic Seismic Hazard Assessment ................................................................................................... 118
8.1 Interpretation of Eurocode 8 for the case of production-induced seismicity ....................................... 118
8.2 Hazard assessment: summary of approach and method implemented ............................................. 118
8.3 Hazard maps: PGA and PGV for a 475 year return period ............................................................ 119
8.4 Sensitivity tests ........................................................................................................................... 122
8.5 Assumptions and limitations ........................................................................................................ 123
8.6 Time evolution of seismic hazard: projections based on planned production .................................... 124
8.7 PGA hazard assessment ............................................................................................................. 124
8.8 Logic-tree to assess epistemic uncertainties ................................................................................... 127
8.8.1 Classification of epistemic uncertainties ........................................................................................ 127
8.8.2 Topology of the logic-tree ........................................................................................................... 129
8.8.3 Elements of the logic-tree ............................................................................................................ 130
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8.8.4 Results of the logic-tree ............................................................................................................... 135
8.9 Seismic hazard assessments for different pressure depletion scenarios ............................................. 136
8.9.1 Seismological assessments for each scenario ................................................................................ 136
8.9.2 Ground motion assessments for each scenario .............................................................................. 140
8.10 Hazard Summary ...................................................................................................................... 142
8.11 Conclusions ............................................................................................................................... 143
8.12 Recommendations for further work............................................................................................... 144
8.13 References ................................................................................................................................. 144
9 The Role of Faults .................................................................................................................................... 147
9.1 Introduction ............................................................................................................................... 147
9.2 Seismicity in a geomechanical evaluation framework..................................................................... 147
9.2.1 Stored energy ............................................................................................................................ 148
9.2.2 Failure ...................................................................................................................................... 149
9.2.3 Release of stored energy ............................................................................................................. 149
9.2.4 The role of faults and the release of stored energy in the Groningen field ........................................ 150
9.3 What we know and what we don’t know (yet) .............................................................................. 151
9.3.1 Equilibrium of forces (stress), either statically or dynamically .......................................................... 151
9.3.2 Subsurface structure ................................................................................................................... 152
9.3.3 Material behavior ...................................................................................................................... 152
9.3.4 Loading conditions, initial and production-induced ........................................................................ 153
9.3.5 Monitoring activities and further investigations .............................................................................. 156
9.4 Geomechanical modeling ........................................................................................................... 158
9.4.1 Full 3D modeling ....................................................................................................................... 158
9.4.2 2-Dimensional modeling of fault slip ............................................................................................ 159
9.5 2D Geomechanical investigation of the potential causes of fault slip and seismic events .................... 160
9.5.1 Model features........................................................................................................................... 161
9.5.2 In-situ stress and formation properties .......................................................................................... 163
9.5.3 Model results ............................................................................................................................. 164
9.5.4 Summary of findings 2D modeling ............................................................................................... 169
9.5.5 Next steps 2D modeling ............................................................................................................. 170
9.6 Three-dimensional modelling results ............................................................................................. 172
9.6.1 Geomechanical assessment of seismicity with full field geomechanical model (URC) .......................... 172
9.6.2 Geomechanical assessment of seismicity with full field geomechanical model ................................... 179
9.7 Conclusions ............................................................................................................................... 183
9.8 References ................................................................................................................................. 184
10 Reducing the Remaining Uncertainty in the Hazard..................................................................................... 185
10.1 Introduction ............................................................................................................................... 185
10.2 Data acquisition activities ........................................................................................................... 185
10.2.1 Introduction ............................................................................................................................... 185
10.2.2 Extension passive seismic network ............................................................................................... 185
10.2.3 Subsurface vertical seismic arrays ................................................................................................ 186
10.2.4 Temporary vertical seismic arrays ................................................................................................ 187
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10.2.5 Permanent vertical seismic arrays ................................................................................................ 187
10.3 The 2014 Study and Data Acquisition program on Induced earthquakes in the Groningen field ........ 187
10.3.1 Geomechanical discussion to reduce uncertainty in the partitioning factor ....................................... 188
10.3.2 Continuation of the Study Program .............................................................................................. 190
10.4 References ................................................................................................................................. 192
11 Appendix A: Full 3D geomechanical modeling methodology ....................................................................... 193
11.1 Introduction ............................................................................................................................... 193
11.2 Geological model input .............................................................................................................. 193
11.3 Material properties .................................................................................................................... 194
11.4 Initial stress state ........................................................................................................................ 197
11.5 Global model analysis methodology ............................................................................................ 198
11.6 Sub-model analysis methodology ................................................................................................ 203
12 Appendix B: Pressure Maintenance ........................................................................................................... 209
12.1 Introduction ............................................................................................................................... 209
12.2 References: ................................................................................................................................ 209
12.3 Selection of the injection medium ................................................................................................. 209
12.4 Nitrogen (N ) ............................................................................................................................ 210
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12.5 Carbon dioxide (CO ) ................................................................................................................ 211
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12.6 Flue Gas and Air ....................................................................................................................... 211
12.7 Conclusion ................................................................................................................................ 211
12.8 Gas recovery with nitrogen injection. ........................................................................................... 212
12.9 Introduction ............................................................................................................................... 212
12.10 Objectives of the subsurface study ............................................................................................... 213
12.11 Basis for modelling ..................................................................................................................... 213
12.12 Simulation workflow ................................................................................................................... 216
12.12.1 Test model ................................................................................................................................. 216
12.12.2 Full Field Model (FFM) ................................................................................................................ 218
12.13 Results and observations ............................................................................................................. 220
12.14 Alternative Development Options ................................................................................................. 223
12.14.1 Partial Voidage Replacement ...................................................................................................... 223
12.14.2 Injection in the northern part of the field only ................................................................................ 224
12.14.3 Different start up times for the injection ......................................................................................... 227
12.14.4 Summary of the development options. .......................................................................................... 227
12.15 Development plan for pressure maintenance using nitrogen injection .............................................. 228
12.16 Technical premises ..................................................................................................................... 228
12.17 Non-technical premises .............................................................................................................. 228
12.18 Assumptions .............................................................................................................................. 228
12.19 Development concept ................................................................................................................. 229
12.19.1 Plot lay-out ................................................................................................................................ 229
12.19.2 Injection wells ............................................................................................................................ 230
12.19.3 Air Separation Units (ASU) ......................................................................................................... 231
12.19.4 Nitrogen Rejection Unit (NRU) ..................................................................................................... 232
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12.19.5 Pipeline infrastructure ................................................................................................................. 233
12.19.6 Project Execution planning .......................................................................................................... 234
12.19.7 Operations and maintenance ...................................................................................................... 234
12.19.8 High level development cost estimate (screening level) ................................................................... 234
12.20 Project uncertainty...................................................................................................................... 235
12.21 Project optimisation .................................................................................................................... 236
12.22 Environmental and societal impact ............................................................................................... 236
12.23 Gas recovery with water injection ................................................................................................ 237
12.24 Conclusions ............................................................................................................................... 238
12.25 References ................................................................................................................................. 239
13 Appendix C: Conclusions / Insights .......................................................................................................... 240
13.1 Maximum possible magnitude ..................................................................................................... 240
13.2 Probabilistic seismological assessment .......................................................................................... 241
13.3 Probabilistic seismic hazard assessment ....................................................................................... 241
13.4 Remaining technical uncertainties ................................................................................................ 242
13.5 Future data gathering designed to reduce uncertainties .................................................................. 242
13.6 References ................................................................................................................................. 243
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0 Executive Summary
0.1 Background
This report provides technical support for the update of the Groningen Winningsplan of 1st December 2013
and contains details of the analysis of subsidence and earthquakes induced by gas production from the
Groningen field. This report presents the significant study progress on:

Results of geomechanical and seismological studies into induced earthquakes in the Groningen field
based on the historical earthquake record with forecasts of future seismicity

Results of the analysis of compaction of the reservoir rock and subsidence with forecasts of future
subsidence

Impact of different depletion scenarios and the application of pressure maintenance on the seismic
hazard
In a letter to Parliament (11th February 2013 reference TK 2012-2013 33529, no. 2), the Minister of
Economic Affairs initiated a number of studies on induced earthquakes in the Groningen area. Study
number 5 addresses “research into the maximum strength of earthquakes associated with the Groningen
gas field”. Study number 6 addresses “research into different production methods to reduce the number
and magnitude of earthquakes”. A Technische Begeleidingscommissie Ondergrond (TBO; Technical
Guidance Committee Sub-surface) and Steering Committee were set up by the Minister of Economic Affairs
to oversee this study work and ensure quality and independence. The results of these studies 5 and 6 have
been summarised in this report.
0.2 Introduction
Although considerable progress was made in the understanding of the seismic hazard, uncertainty remains
at present. Note that the uncertainty range around the seismic hazard (and hence predictions around the
maximum) is not constant but instead grows in the future (even in the next 5 to 10 years). This increasing
uncertainty, however, is intended to be balanced by an overall programme to further calibrate and validate
assumptions and to take appropriate preventive measures, where acceptable limits may be exceeded.
The scientific knowledge and uncertainty range described in this report reflects the current level of
understanding, but not necessarily the true physical uncertainty. Consequently, predictions of the seismic
hazard range are believed to be conservative. To reduce the uncertainty NAM has initiated a further data
acquisition programme to obtain additional field data, as well as a studies programme. Once the
uncertainty is reduced, the conservatism and related preventive measures may be scaled down accordingly.
The execution of the field data acquisition plan and the integration of data in the studies program will be
secured in the monitoring protocol as addendum to the Winningsplan (the “Beheersprotocol voor Borging
van het Seismisch Risico binnen grenzen”, (Ref. 1)). This protocol and associated monitoringsplan contain a
proposal on how to validate, update and report the risk assessment and related key assumptions on an
annual basis. This is expected to result in a continuous improvement and more constrained assessment of
the seismic hazard over the coming years.
0.3 Historical Seismicity in the Groningen field
Since the early nineties, relatively small earthquakes have occurred in the vicinity of the Groningen gas
field. It is recognized that these events are induced by the production of gas from the field. In 1993, a
geophone monitoring network, operated by KNMI, was installed in the field. This was extended several
times and has a detection limit of M=1.5 since 1996. Several cases of earthquakes induced by gas
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production have been recorded in literature. A possible analogue for larger earthquakes in the Groningen
area is the 2004 earthquake of magnitude M =4.4 in the Rotenburg gas field (Germany), which also
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produces from the Rotliegend.
The earthquake in the Huizinge area on the August 16th, 2012 was the strongest event recorded to date in
the Groningen Province with magnitude M =3.6 and caused damage to buildings and raised significant
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public concerns and subsequent feelings of fear.
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