PART I- Formation of Clay Seal Properties: Theoretical Fundamentals 1. Composition of Clay Sediments and Their Structure Formation in Sedimentogenesis 2. Lithogenesis of Clay Sediments 3. Formation of the Properties of Clay Seals in Lithogenesis PART II- Characteristsic of The Facies Types of Clay Seals 4. Deposititional Environments of Clay Seal Formation 5. Facies Analysis of Clay Seals in Oil- and Gas-bearing Basins 6. The Composition of the Facies Types of Clay Seals and Its Change With Depth 7. Structure and Properties of the Facies Types of Clay Seals PART III- Modeling of the Change in the Clay Seal Properties in Lithogenesis8. Physiochemical Models of Clay Rock Microstructures 9. Development of a Mathematical Model for Estimating the Strength of Clay Seals 10. Comparison of Theoretical Calculation Results and Experimental Data on the Mechanical Strength of Clay Seals