Clay Seals of Oil and Gas Deposits

V. I. Osipov, V.N. Sokolov and V.V. Eremeev

Published on Monday, 17 October 2011 20:05

In this work, the formation of clay deposits in sedimentary basins and the transformation of their mineral composition, microstructure and water content in the course of lithogenesis are treated in relation to the occurrence of oil and gas deposits.

Major topics discussed in this book comprise revealing of the main regularities in the variation of physical, mechanical, and seepage properties of clay in relation to its occurrence depth. In addition, a close relationship is demonstrated between clay deposit transformations and clay composition, thermodynamic conditions, pore space, structural bonds and geo-chemical composition of porous solutions. Facies conditions of clay seal development are also analysed and the relation between the cyclic structure of sedimentary massifs and sedimentary basin evolution is described. To this end, seven facies types of clay seals that differed with regard to composition, formation conditions, and screening properties have been distinguished by facies analysis of more than forty sedimentary oil-and-gas bearing basins within the former USSR territory. Also the correlation between clay properties and clay occurrence depth per seal type and the main factors controlling intensification and degradation of screening properties are described and it is shown that the maximum clay screening effect depth is an important indicator in the occurrence of oil and gas deposits. Information on modelling of the structure, properties and transformations of clay seals at various depths is included in the final part of the work. In this respect, also data like clay porosity graphs and strength variation at different lithogenesis stages are provided and the prediction of screening properties of clay seals with the help of software that was developed by the authors is treated.

This practical and informative book is intended for (post)graduate students, researchers and professionals in oil and gas geology, lithology, enineering geology and hydrogeology worldwide.

Contents

Introduction VII
PART I FORMATION OF CLAY SEAL PROPERTIES: THEORETICAL FUNDAMENTALS 1
Chapter 1 Composition of Clay Sediments and Their Structure Formation in Sedimentogenesis 3
1.1. Composition of clay sediments 3
1.2. Structure of clay sediments 7
1.3. The theory of structure formation in clay dispersions 17
1.4. Structural bonds 26
1.5. Formation of primary microstructures in clay sediments 30
Chapter 2 Lithogenesis of Clay Sediments 37
2.1. General information 37
2.2. The stages of lithogenesis 38
2.3. Boundaries between the stages and substages of lithogenesis 64
Chapter 3 Formation of the Properties of Clay Seals in Lithogenesis 71
3.1. Density and porosity 71
3.2. Water content and consistence 83
3.3. Permeability 90
3.4. Physical-mechanical properties 97
3.5. Rheological properties 109
3.6. General regularities in the formation of clay properties in the process of lithogenesis 112
PART II CHARACTERISTIC OF THE FACIES TYPES OF CLAY SEALS 119
Chapter 4 Depositional Environments of Clay Seal Formation 121
4.1. The cyclic structure of sedimentary basin sequences 121
4.2. Source provinces r , 123
4.3. Evolution of sedimentation basins 125
4.4. Classification of clay seals according to their depositional environments and screening properties 131
Chapter 5 Facies Analysis of Clay Seals in Oil-and Gas-Bearing Basins 137
5.1. The principal criteria for facies analysis 137
5.2. Facies analysis of clay seals in sedimentary basins 139
VI CONTENTS
Chapter 6 The Composition of the Facies Types of Clay Seals and Its Change
with Depth		 147
6.1. The composition of the facies types of clay seals 147
6.2. A comparative characteristic of the composition of clay seals
of various facies types		 158
Chapter 7 Structure and Properties of the Facies Types of Clay Seals 163
7.1. The influence of depositional environments on the
structure formation		 163
7.2. Porosity 172
7.3. Microfracturing 181
7.4. Permeability 188
7.5. Destruction of clay seals of different facies types 190
PART III MODELING OF THE CHANGE IN THE CLAY SEAL PROPERTIES IN LITHOGENESIS 195
Chapter 8 Physicochemical Models of Clay Rock Microstructures 197
8.1. The concepts of the physicochemical mechanics of clay rocks
as a basis for modeling		 197
8.2. Calculation of the number of contacts 198
8.3. Strength of individual contacts between clay particles 204
Chapter 9 Development of a Mathematical Model for Estimating the Strength of Clay Seals 211
9.1. Theoretical calculation of the change in the strength of individual contacts with depth 211
9.2. Calculation of the change in the number of contacts in clay seals with depth 225
9.3. Theoretical calculation of tensile and compressive strength of clay seals 229
Chapter 10 Comparison of Theoretical Calculation Results and Experimental Data on the Mechanical Strength of Clay Seals 239
10.1. Experimental data base 239
10.2. Comparison of theoretical and experimental data 239
References 259
Subject Index 275