deformation of chalk through compaction ani) flow.

413 Pages·2008·40.72 MB·English

like to thank Oystein Dretvik, Eric Mathiesen and Per Erik Overli and in particular
Kjetl Tonstad and Ole Preben Berget for their help and assistance over the past three
years. For the work undertaken with Norsk Hydro, one person in particular deserves a
special mention, Knut Pederstad. Core analysis, in particular that involving North Sea
chalk, is a time consuming and often confusing business. I was very fortunate to have a
great deal of guidance from Tony Corrigan, who never failed to help me when ever I
needed it to unravel the complex story locked in the chalk cores. I was also fortunate
to be able to observe Dr Jim Kennedy from Oxford at work on the same core material.
His comments and observations proved to be extremely useful.
A substantial part of the work reported in this thesis represents laboratory experiments
conducted in the Soil Mechanics Laboratory, Department of Civil Engineering, Im-
perial College, London. Although this is not my parent department, the technical sup-
port provided has been unstinting. Without the unending help of Louis Spall, Steve
Ackerley, Graham Keefe and Alan Bolser, this study could not have been completed.
They have always been willing to rescue me when the machinery I was using broke down
(a frequent occurrence) and help with any modifications that were needed with the min-
imum of delay. The members of staff within the Soil Mechanics section, in particular
Dr's Angus Skinner, Dave Potts, Professors's Peter Vaughan and John Burland have
also been incredibly patient in answering questions, explaining principles and turning
a blind eye to the innumerable oil spillages with which I have been closely associated.
The technical staff at University College have shown the same level of patience as that
exhibited by those at Imperial College. Three people deserve a special mention, Sean
Houlding, Mike Gray and Ron Dudman. Ron in particular, has never ceased to amaze
me with his immense enthusiasm and encouragement, even though my requests for the
impossible frequently ended with a his owning more oil stained clothes.
I have been extremely privileged to work in a research group in which help and co-
operation has never been in short supply. I would like to thank to past members of our
research group, Tony Addis for his initial help and encouragement, Najwa Yassir for
her assistance in a number of experiments, the many useful discussions and her
friendship. A special thank you should also go to Tony Goldsmith. He has helped me
with a large number of experiments, equipment development and has always been will-
ing to rewrite sections of the database program he has been developing when I needed
specific information. The biggest thank you of all goes to Meryvn Jones. Without his
(and that of his wife Jane's) help, assistance, insistence and support this project would
never have materialised. I would also like to thank Sediment Deformation Research
for funding this project and for allowing me the privilege of working within such a
dynamic and successful research group.
As such occassions are rare, I should take this opportunity to thank a number of people
who, through their inspiration, have been the key to the maintenance of my sanity. They
are too numer ous to mention, but include such names as Camm, Bishop, Chadwick
and most important of all Mitchell.
Finally, I would like thank my family for all of their encouragement during my studies
and in particular my wife Ann. Without her never ending support rone of this would
have been possible. This thesis can only be a small reward for all that she has willingly
given up to help me during my time at University.
CONTENTS
Page No.
CHAPTER 1
INTRODUCTION . 1
1.1. Research objectives . 1
1.2. Organisation of thesis .............................................................................4
1.3. Scientific rationale .....................................................................................6
PART 1 ON ThE NATURE OF CHALK.
CHAPTER 2
STRATIGRAPHY AND STRUCTURAL SETJ1NG OF ThE CHALKS
OF NORTH WEST EUROPE.
2.1. Introduction ..............................................................................................12
2.2. Structural control ..........................................................................................13
2.3. The initial accumulation and diagenesis of the chalk ................................16
2.4. Danish onshore chalks (Stevn's Klint) ........................................................23
2.5. Onshore chalks from South East England (Buster Hill) ............................25
CHAPTER 3
NORWEGIAN HYDROCARBON RESERVOIR CHALKS.
3.1. Introduction ..................................................................................................29
3.2. Sedimentology .........................................................................................29
3.2.1. Autochthonous chalks ................................................................................31
3.2.2. Allochthonous chalks ................................................................................34
3.3. Structural development and overpressuring................................................42
3.4. The lithostratigraphic characteristics of the Norwegian
chalkformation s ............................................................................................. 58
3.4.1. Hidra Formation (Cenomanian) ..............................................................60
3.4.2. Plenus Marl Formation (Cenomanian) .................................................60
3.4.3. Hod Formation (Turonian to Upper Campanian) ................................60
3.4.4. Tor Formation (Upper Campanian to Maastrichtian) ..........................61
3.4.5. Ekofisk Formation (Danian, Tertiary) ...................................................62
3.5. Fracture studies ..........................................................................................62

3.5.1. Lithological and fracture study of well 2/7-Bli 65
PART 2 EXPERIMENTAL STUDIES.
CHAPTER 4
UNIAXIAL EXPERIMENTS.
4.1. Introduction ...............................................................................................104
4.2. Resume of uniaxial strain: theory and practice ........................................106
4.3. Experimental equipment and sample preparation methodology ............117
4.3.1. The triaxial cell .......................................................................................117
43.2. Measurement of horizontal and vertical displacements ......................119
43.3. The load frame ..................................................................................122
4.3.4. The drainage system ............................................................................122
4.3.5. Data logging ...........................................................................................122
43.6. Sample preparation and installation procedures ....................................123
4.4. Slow strain-rate experiments ..................................................................124
4.4.1. Introduction .............................................................................................124
4.4.2. Experimental methodology and results ................................................127
4.4.2.1. Elongcl ............................................................................................131

4.4.2.2. E longc 2 ..........................132

4.4.23. Elongc3 ....................137

4.4.2.4. Elongc4 .............................137

4.4.3. Discussion 137
4.5. Stress relaxation experiments . 144
43.1. Introduction ..........................................................................................144
4.5.2. Experimental results ...........................................................................145
4.5.2.1. Vertical effective stress/axial strain ............................................ 145
4.5.2.2. Horizontal and vertical effective stress .........................................149
43.2.3. Deviatoric/mean effective stress ....................................................149
4.5.2.4. Void ratio/mean effective stress ......................................................157
4.6. Water injection experiments ...................................................................157
4.6.1 Introduction ..........................................................................................157
4.6.2 Experimental results ...........................................................................161
4.7 Discussion .............................................................................................173
CHAPTER 5
DETERMINATION OF RESERVOIR ROCK PERMEABILITY.
5.1. Introduction ........................................................................................186
5.2. Routine permeability analysis ............................................................189
5.3. High pressure falling-head methodology ...........................................192
5.4. High pressure constant-head equipment ..............................................192
5.5. High pressure constant-head methodology ...........................................193
5.6. Sample morphology ..............................................................................195
5.7. Experimental results ...........................................................................197
5.8. Microfacies analysis ...............................................................................230
5.9. Discussion and conclusions ..............................................................232
CHAPTER 6
UNDRAINED SHEAR EXPERIMENTS
6.1. Introduction .........................................................................................241
6.2. Resume of the theoretical background of undrained shear behaviour 247
63. Previous studies on the undrained shear behaviour of
calcareoussediments ............................................................................254
6.4 . Methodology . 266
6.5. Experimental results ......................................................................268
6.5.1. Isotropically consolidated samples .............................................269
63.2. Anisotropically consolidated samples ..........................................277
6.5.3. Strain rate data ..........................................................................289
6.6. Discussion ...................................................................................294
6.6.1. The critical state for an elastic material ................................298
6.6.2. Influence of consolidation pressure on failure ..........................300
6.6.2.1. Butser Hill ..............................................................................302
6.6.2.2.. Stevn's Klint ............................................................................307
6.63. Influence of method of consolidation on the stress path .........309
6.6.4. Influence of consolidation pressure on pore
pressuregeneration ..........................................................................312
6.6.5. The influence of strain rate ..................................................... 315
6.6.6. Failure surface and consolidation path ....................................317
6.7. Conclusions ...............................................................................327
CHAPTER 7
GENERAL DISCUSSION AND CONCLUSIONS
7.1. Introduction ................................................................................331
72.Burial compaction and shear deformation during
redeposition.....................................................................................332
73.Reservoir compaction and sea floor subsidence ......................337
73.1. Introduction ..............................................................................337
7.32. Surface subsidence over chalk oil fields .................................338
7.3.2.1. History of the Ekofisk subsidence ..........................................338
732.2. Subsidence history of West Ekofisk......................................340
7.323. Subsidence history of ValhaII .................................................340
73.2.4. Causes of the sea floor subsidence ........................................340
733. Analysis and prediction of subsidence ......................................342
7.3.3.1. The finite element models . 342
7.3.3.1.1. The geology and model geometries ....................................342
7.3.3.1.2. Mechanical behaviour of the reservoir rock ........................343
7.3.3.1.3. Mechanical behaviour of the overburden rock ...................345
7.33.1.4. Pore fluid pressures ...............................................................347
7.3.3.2. Running the analysis .................................................................347
7.3.4. Results ......................................................................................347
7.3.4.1. Ekoflsk subsidence ..................................................................348
7.3.4.2. West Ekofisk subsidence ........................................................252
73.4.3. Eldflsk subsidence ....................................................................352
73.4.4. VaThall subsidence ..................................................................354
73.5. Discussion of chalk oil field compaction and subsidence ........354
7.4. Flow of chalk in the near well bore region.................................... 357
BIBUOGRAPHY............................................................................... 359
APPENDIX 1. Geological characterisation of outcrop chalks ...........369
FIGURES.
Figure. 1.1. Location map of the Greater Ekofisk area.
Figure. 2.1. Structural map for the Late Cretaceous. (After Hancock, 1987.)
Figure. 3.1. Location map of the Greater Ekofisk Area.
Figure. 3.2. Schematic map indicating the predominant direction of sediment transpor-
tation and re-deposition during the deposition of the Tor Formation Chalks. (After
Kennedy, 1987 a/b.)
Figure. 3.3. Four maps indicating the increasing intensity of allochthonous deposition,
particularly around the Lindesnes Ridge, during the deposition of the Tor Formation
Chalks. (After Hatton, 1986.)
Figure. 3.4. Schematic map indicating the predominant direction of sediment transpor-
tation and re-deposition during the deposition of the Lower Ekofisk Formation Chalks.
(After Kennedy, 1987 a/b.)
Figure. 3.5. Schematic map based on isopach thicknesses indicating re-deposition
during the deposition of the Upper Ekofisk Formation Chalks. (After Hatton, 1986.)
Figure. 3.6. Burial/effective stress curves assuming that overpressuring is related to
burial rate, migration of hydrocarbons and increasing maturation pressure. (After
Watts, 1983.)
Figure. 3.7. A generalised stratigraphic correlation between the chalks of the North Sea
and those found in South East England.
Figure. 3.8. A log of well 2/7-B 11 constructed to indicate facies control on fracture
development.
Figure. 4.1. Graph of horizontal effective stress/vertical effective stress for a 38%
porosity chalk.
Figure. 4.2. Graph of horizontal effective stress/vertical effective stress for three sample
with different initial porosities (28,38 and 48%).
Figure. 4.3. Graph of deviatoric stress/mean effective stress for a 38% porosity chalk.
Figure. 4.4. Graph of deviatoric stress/mean effective stress for a 48% porosity chalk.
Figure. 4.5. Graph of deviatoric stress/mean effective stress for a 28% porosity chalk.
Figure. 4.6. Graph of deviatoric stress/mean effective stress for three samples with dif-
ferent initial porosities (28, 38% and 48%).
Figure. 4.7. Graph of void ratio/mean effective stress for a 38% porosity chalk.
Figure. 4.8. Graph of void ratio/mean effective stress for a 28% porosity chalk.
Figure. 4.9. Graph of void ratio/mean effective stress for a 48% porosity chalk.
Figure. 4.10. Graph of void ratio/mean effective stress for three samples with different
initial porosities (28,38 and 48%).
Figure. 4.11. Cam Clay model (After Atkinson and Bransby, 1978).
Figure. 4.12. Schematic representation of the high triaxial cell used during this study.
Figure. 4.13. Sectioned drawing of a balanced ram.
Figure. 4.14. Schematic representation of a radial strain belt.
Figure. 4.15. Sectioned drawing of an Imperial College volume gauge.
Figure. 4.16. Schematic drawing of a sample assembled in the triaxial cell.
Figure. 4.17. Graph of vertical effective stress/axial strain for slow strain-rate experi-
ment ELONGC1.
Figure. 4.18. Graph of horizontal effective stress/vertical effective stress for slow strain-
rate experiment ELONGC1.
Figure. 4.19. Graph of deviatoric stress/mean effective stress for slow strain-rate experi-
ment ELONGC1.
Figure. 4.20. Graph of void ratio/mean effective stress for slow strain-rate experiment
ELONGC1.
Figure. 4.21. Graph of vertical effective stress/axial strain for slow strain-rate experi-
ment ELONGC2.
Figure. 4.22. Graph of horizontal effective stress/vertical effective stress for slow strain-
rate experiment ELONGC2.
Figure. 4.23. Graph of deviatoric stress/mean effective stress for slow strain-rate experi-
ment ELONGC2.
Figure. 4.24. Graph of void ratio/mean effective stress for slow strain-rate experiment
ELONGC2.
Figure. 4.25. Graph of vertical effective stress/axial strain for slow strain-rate experi-
ment ELONGC3.
Figure. 4.26. Graph of horizontal effective stress/vertical slow strain-rate effective stress
for experiment ELONGC3.
Figure. 4.27. Graph of deviatoric stress/mean effective stress for slow strain-rate experi-
ment ELONGC3.
Figure. 4.28. Graph of void ratio/mean effective stress for slow strain-rate experiment
ELONGC3.
Figure. 4.29. Graph of vertical effective stress/axial strain for slow strain-rate experi-
ment ELONGC4.
Figure. 4.30. Graph of horizontal effective stress/vertical effective stress for slow strain-
rate experiment ELONGC4.
Figure. 4.31. Graph of deviatoric stress/mean effective stress for slow strain-rate experi-
ment ELONGC4.
Figure. 4.32. Graph of void ratio/mean effective stress for slow strain-rate experiment
ELONGC4.
Figure. 4.33. Graph of vertical effective stress/axial strain which compares the result of
slow strain-rate experiment ELONGC1 with samples of equivalent initial porosities.
Figure. 4.34. Graph of vertical effective stress/axial strain which compares the result of
slow strain-rate experiment ELONG2 with samples of equivalent initial porosities.
Figure. 4.35. Graph of vertical effective stress/axial strain which compares the result of
slow strain-rate experiment ELONGC3 with samples of equivalent initial porosities.
Figure. 4.36. Graph of vertical effective stress/axial strain which compares the result of
slow strain-rate experiment ELONGC4 with samples of equivalent initial porosities.
Figure. 4.37. Graph of vertical effective stress/axial strain for stress relaxation experi-
ment VOBC5.
Figure. 4.38. Graph of vertical effective stress/axial strain for stress relaxation experi-
ment VOBC7.
Figure. 4.39. Graph of vertical effective stress/axial strain for stress relaxation experi-
ment VOHC2.
Figure. 4.40. Graph of vertical effective stress/axial strain for stress relaxation experi-
ment VOHC3.
Figure. 4.41. Graph of vertical effective stress/axial strain for stress relaxation experi-
ment VOTC1.
Figure. 4.42. Graph of horizontal effective stress/vertical effective stress for stress
relaxation experiment VOBC5.
Figure. 4.43. Graph of horizontal effective stress/vertical effective stress for stress
relaxation experiment VOBC7.
Figure. 4.44. Graph of horizontal effective stress/vertical effective stress for stress
relaxation experiment VOHC2.
Figure. 4.45. Graph of horizontal effective stress/vertical effective stress for stress
relaxation experiment VOHC3.