Shale engineering : mechanics and mechanisms

Shale makes up about three-fourths of drilled formations. Even though the engineering properties of shale have been studied for several decades, shale engineering is still prone to unexpected instabilities and delays, representing a serious problem for the petroleum, mining and civil engineering industry. Distinct characteristics of shale make it exceptionally difficult to work with; three categories of potential stability problems in shale are mechanical problems, chemical reactivity and swelling, and thermal stimulation. When a number of these problems occur simultaneously, finding an optimized solution becomes even more challenging.

Shale Engineering provides an integrative engineering approach to work towards practical solutions in handling shale. Accordingly, shale is defined and described from both an engineering and geological point of view. Elasticity and poroelasticity concepts, shale's response to temperature changes, and finally chemical properties of shale and the impact thereof on the rock's behavior are discussed in detail.

In addressing the engineering aspects and parameters related to chemical, mechanical and thermal properties and integrating them into engineering models that can be applied in deep engineering projects, mining and other civil works, this book will serve as a reference to model designers and engineers working with shale in the petroleum industry and elsewhere. It is also suited for use in academic and professional courses in petroleum, mining, geological and civil engineering and drilling.

Author Notes

Mohammad Reza Asef obtained his BSc degree from Shahid Bahonar University of Kerman in Iran, an MSc in Engineering geology from ITC-Delft in the Netherlands, and a PhD from the University of Nottingham in the UK. Currently, he is assistant professor in Engineering Geology at Tarbiat Moallem University in Tehran, Iran. He is an active researcher and student supervisor in a variety of topics, including applications of rock mechanics, drilling, completion and reservoir evaluation in the petroleum industry.

Mohsen Farrokhrouz obtained his BSc degree from Tehran University in Iran, his MEng in Petroleum Well Engineering from Curtin University of Technology in Australia, and his MSc in Petroleum Drilling Engineering from Petroleum University of Technology in Iran. He is currently working as a well engineer at South Zagros Oil and Gas Production Co, affiliated to NIOC. He is active in various research fields such as application of rock mechanics in petroleum engineering and logging. His work experience covers workover operations, especially wireline services and log running in producing wells, log interpretation and petroleum exploitation.

Preface	p. xiii
1 Insight into shale	p. 1
1.1 What is shale?	p. 2
1.1.1 Shale: quick view	p. 2
1.1.2 Shale: detailed definition	p. 2
1.2 Shale minerals	p. 4
1.3 Molecular structure of clay	p. 4
1.4 Varieties of clay minerals	p. 8
1.4.1 Smectite group	p. 8
1.4.2 Vermiculite	p. 9
1.4.3 Kaolin group	p. 9
1.4.4 Illite	p. 10
1.4.5 Interstratified clays	p. 10
1.5 Cation exchange capacity	p. 11
1.6 Cation exchange capacity (CEC) models	p. 12
1.6.1 The general concept of shale formation models	p. 13
1.6.2 Waxman and Smits shale model	p. 15
1.7 Laboratory measurements of cation exchange capacity	p. 17
1.7.1 Background	p. 17
1.7.2 Materials and methods	p. 18
1.7.3 pH control on CEC	p. 18
1.8 Permeability in shale	p. 19
1.8.1 Effect of pressure on permeability	p. 19
1.9 Shale porosity importance	p. 22
1.9.1 Effect of depth and pressure on porosity	p. 22
1.9.2 Importance of micro-fabrics	p. 23
1.9.3 Relationships between porosity and mechanical properties	p. 24
1.9.4 Porosity as a geomechanical index	p. 25
1.10 pH Effect on shear modulus	p. 26
1.11 Shale importance in waste disposal	p. 28
1.12 Significance of shale in the petroleum industry	p. 29
References	p. 31
2 Shale classification	p. 37
2.1 Geological classification of shale	p. 37
2.2 Engineering classification of shale	p. 39
2.2.1 Rock strength	p. 40
2.2.2 Durability and slaking	p. 41
2.2.3 Fissility in comparison with lamination	p. 43
2.2.4 Swelling and shrinkage of clay soil and rock	p. 44
2.2.5 Moisture content	p. 46
2.2.6 Disintegration	p. 47
2.2.7 Excess pore water pressure	p. 48
2.2.8 Common tests performed on shale	p. 49
2.2.9 Integrated shale features consideration	p. 49
2.3 Understanding subsurface shale	p. 52
2.3.1 Inter-layer water in shale	p. 52
2.3.2 Shale compaction	p. 52
2.4 Smectite/illite conversion	p. 54
2.4.1 Classification and general trends	p. 54
2.4.2 Carbonate occurrence in shale	p. 57
2.4.3 Kaolinite response to environmental changes	p. 59
2.4.4 Shale composition and drilling suggestions	p. 59
2.5 Stability diagrams of shale minerals	p. 61
2.6 Kinetics of clay minerals	p. 62
2.6.1 Montmorillonite	p. 62
2.6.2 Illite	p. 64
2.6.3 Kaolinite	p. 65
References	p. 67
3 Swelling fundamentals	p. 73
3.1 Drilling fluids	p. 73
3.2 Shale and drilling muds	p. 76
3.3 Common problems when drilling through shales	p. 77
3.3.1 Mechanical view	p. 77
3.3.2 Practical view	p. 78
3.3.3 Prevention and procurement	p. 80
3.4 Pressure and chemical performance in shale	p. 82
3.5 Transport in shales	p. 83
3.6 Clay-water interactions	p. 86
3.7 Electrical surfaces of clay particles	p. 88
3.8 Clay hydration	p. 88
3.9 Involved forces in swelling	p. 89
3.10 Swelling phenomenon; history and promise	p. 90
3.11 The swelling pressure	p. 92
3.12 Shale effects caused by water activity	p. 95
3.12.1 Capillary effects	p. 95
3.12.2 Concentration effects	p. 97
3.12.3 Coupling: cation exchange process	p. 98
References	p. 99
4 Water activity and osmosis concepts	p. 103
4.1 Osmotic flow and membrane efficiency	p. 105
4.1.1 Membrane efficiency test	p. 106
4.2 Membrane efficiency studies	p. 106
4.3 Swelling and membrane efficiency concepts	p. 109
4.4 Mathematical model of water and solute transport in shale	p. 110
4.4.1 Background theory	p. 110
4.4.2 Basic equations	p. 111
4.4.3 Membrane efficiency	p. 112
4.4.4 Modified diffusion potential	p. 113
4.4.5 Model formulation	p. 114
4.4.6 Boundary conditions and initial condition	p. 116
4.4.7 Numerical solution procedure	p. 116
4.5 Results and discussions	p. 117
4.6 The impact of temperature on the membrane efficiency of shale	p. 126
4.6.1 Membrane efficiency test	p. 127
4.6.2 Temperature impact on the test procedure	p. 127
4.7 Motivation for further research	p. 129
References	p. 130
5 Shale stabilizing additives and systems	p. 133
5.1 Introduction	p. 133
5.2 Shale reactivity test	p. 133
5.2.1 Common tests for shale behavior measurement	p. 134
5.2.2 Test description and results	p. 135
5.3 Salts	p. 138
5.3.1 Potassium chloride	p. 138
5.3.2 Sodium chloride	p. 139
5.3.3 Calcium/magnesium/zinc chloride/bromide (CaCl 2 , CaBr 2 , ZnCl 2 , MgCl 2 , MgBr 2 , ZnBr 2 )	p. 140
5.3.4 Formate and acetate salts (MCOOH, MCH 3 COOH; M = Na + , K + , Cs + )	p. 140
5.3.5 Polymers with special shale affinity (e.g. cationics, amines, PHPA)	p. 140
5.3.6 Asphaltenes, gilsonites, graphites	p. 141
5.4 Sugars and sugar derivatives	p. 141
5.4.1 (Poly-)glycerols and (poly-)glycols	p. 142
5.4.2 Mixed polyol-salt systems	p. 143
5.5 Silicates	p. 143
5.6 Classifying mud systems	p. 144
5.6.1 Type I: non-inhibitive, dispersed/dispersive WBM	p. 145
5.6.2 Type II: conventional inhibitive WBM	p. 146
5.6.3 Type in: osmotic WBM	p. 146
5.6.4 Type IV: low/non-invading WBM/OBM	p. 146
5.6.5 Type V: low/non-invading osmotic WBM/OBM	p. 147
References	p. 147
6 Thermal effects	p. 149
6.1 Preliminary equations	p. 150
6.1.1 Basic equations	p. 150
6.1.2 Field equations	p. 151
6.2 Mathematical modeling	p. 152
6.3 Modeling results	p. 158
6.3.1 Thermally-induced pore pressure	p. 158
6.3.2 Collapse failure index (FI)	p. 161
6.3.3 Critical mud-weight predictions	p. 162
6.3.4 Remarks and limitations	p. 166
References	p. 167
7 Application of Biot theory in wellbore failure models	p. 169
7.1 Poroelasticity: theory and application	p. 169
7.2 Definition of typical wellbore models	p. 170
7.3 Rock failure and failure potential fundamentals	p. 173
7.4 Pure poroelastic effects	p. 175
7.4.1 Constitutive equations	p. 175
7.4.2 Field equations	p. 176
7.4.3 Failure potentials	p. 177
7.5 Poro-thermo-elastic model	p. 178
7.5.1 Constitutive equations	p. 178
7.5.2 Transport equations	p. 179
7.5.3 Conservation equations	p. 179
7.5.4 Field equations	p. 179
7.5.5 Failure potentials	p. 179
7.6 Chemo-poro-elastic model	p. 180
7.6.1 Constitutive equations	p. 181
7.6.2 Transport equations	p. 181
7.6.3 Conservation equations	p. 182
7.6.4 Field equations	p. 182
7.6.5 Failure potentials	p. 183
7.7 Chemo-poro-thermo-elastic model	p. 183
7.7.1 Rock constitutive equations	p. 183
7.7.2 Transport equations	p. 185
7.7.3 Field equations	p. 187
7.7.4 Failure potentials	p. 188
7.8 Useful operational recommendations	p. 191
7.8.1 Uncoupled thermo-poro-elasticity	p. 192
7.8.2 Uncoupled chemo-poro-elasticity	p. 192
7.8.3 Coupled chemo-poro-thermo-clasticity	p. 194
References	p. 196
8 Chemo-mechanical modeling	p. 199
8.1 Introduction	p. 199
8.2 Osmosis and poroelasticity	p. 200
8.3 First instability origin: pore pressure propagation	p. 200
8.3.1 Near wellbore stress distribution	p. 200
8.3.2 Compressive failure criterion	p. 202
8.3.3 Theory and model construction	p. 203
8.3.4 Estimating model input parameters	p. 204
8.4 Results and discussion	p. 204
8.4.1 Input data	p. 204
8.4.2 Pore pressure profile	p. 204
8.4.3 Types of wellbore failure	p. 205
8.4.4 What happens after failure	p. 208
8.4.5 The effect of mud weight	p. 208
8.4.6 The effect of shale properties	p. 209
8.4.7 The effect of solute diffusivity	p. 210
8.4.8 The effect of drilling fluid solute concentration	p. 210
8.4.9 The effect of ¿ H and ¿ h	p. 211
8.5 Second instability origin: solute diffusion	p. 211
8.6 Ion transfer	p. 213
8.6.1 Constitutive equations	p. 213
8.6.2 Transport process	p. 216
8.6.3 Field equations	p. 217
8.7 Wellbore stress analysis	p. 218
8.7.1 Solution methodology	p. 219
8.8 Example application	p. 220
References	p. 224
9 Plane strain solution in time domain	p. 227
9.1 Temperature and solute mass fraction impacts on pore pressure	p. 229
9.2 Chemical and thermal induced stresses	p. 231
9.2.1 Radial stress	p. 231
9.2.2 Tangential stress	p. 233
9.2.3 Axial stress	p. 236
9.3 Strain induced under symmetric loading	p. 237
9.3.1 Radial strain	p. 237
9.3.2 Tangential strain	p. 239
References	p. 240
Appendix I p. 241
Appendix II p. 245
Appendix III p. 251
Appendix IV p. 255
Appendix V p. 257
Appendix VI p. 265
Appendix VII p. 275
Appendix VIII p. 283
Subject index	p. 285

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Table of Contents