Diagenesis and Sequence Stratigraphy : an integrated approach to constrain evolution of reservoir quality in sandstones

Sammanfattning: Diagenesis and sequence stratigraphy have been formally treated as two separate disciplines in sedimentary petrology. This thesis demonstrates that synergy between these two subjects can be used to constrain evolution of reservoir quality in sandstones. Such integrated approach is possible because sequence stratigraphy provides useful information on parameters such as pore water chemistry, residence time of sediments under certain geochemistry conditions, and detrital composition, which ultimately control diagenesis of sandstones. Evidence from five case studies and from literature, enabled the development of a conceptual model for the spatial and temporal distribution of diagenetic alterations and related evolution of reservoir quality in sandstones deposited in paralic environments. Diagenetic alterations that have been constrained within the context of sequence stratigraphy include: (i) formation of kaolinite and intragranular porosity, and mechanical infiltration of clay minerals in sandstones lying at variable depths below sequence boundaries, (ii) formation of pseudomatrix and cementation by calcite, dolomite, and siderite in lag deposits at parasequence boundaries, (iii) cementation by kaolinite, pyrite, and calcite in sandstones lying in the vicinity of parasequence boundaries with coal deposits, (iv) formation of glaucony in condensed interval at parasequence boundaries, transgressive and maximum flooding surfaces, (v) formation of berthierine in fluvial-dominated deltaic deposits of the highstand systems tract, (vi) cementation by calcite in bioclastic sandstones of the transgressive systems tract, and (vii) formation of kaolinite in fluvial deposits of the lowstand systems tract. The distribution of such alterations put important constrains for the pattern of burial diagenesis (e.g., formation of chlorite, illite, quartz), related evolution of reservoir quality in sandstones, and distribution of baffles and barriers for fluid flow in the context of sequence stratigraphy.