ABSTRACT

Sandstones that share common detrital mineralogies, depositional environments, and burial histories also share common diagenetic histories. A survey of the diagenetic history of 100 sandstones from around the world has recognized five common, repetitive, and predictable styles of diagenesis in which similar diagenetic mineral assemblages have been observed.

The five diagenetic styles are: (1) quartz, commonly with lesser quantities of neoformed clays (e.g., kaolinite and/or illite) and late-diagenetic, ferroan carbonate; (2) clay minerals (illite or kaolinite) with lesser quantities of quartz or zeolite and late-diagenetic carbonate; (3) early diagenetic (low-temperature) grain-coating clay mineral cements such as chlorite, which may inhibit quartz cementation during later burial; (4) early diagenetic carbonate or evaporite cement, often localized, which severely reduces porosity and net pay at very shallow burial depths; and (5) zeolites, which occur over a wide range in burial temperature, often in association with abundant clay (usually smectite or chlorite) and late-diagenetic, nonferroan carbonates.

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The quartz diagenetic style is the most common and accounts for 40% of the sample set. It is also most likely to occur in mineralogically mature sandstones, while early diagenetic carbonates and zeolites dominate in mineralogically immature sandstones. Presence or absence of clay appears to be independent of both initial sand mineralogy and depositional environment. However, when clay is present, the type appears to vary as a function of initial sand mineralogy and depositional environment.

Large quantities of quartz are unusual cements in sequences that have never been hotter than 75°C, while illite precipitation at temperatures below 100°C is rare. Zeolite composition changes systematically from clinoptilolite at 25°C to laumonite at temperatures >100°C.

The repetitive nature and simplicity of these five styles can help predict modifications in reservoir quality due to burial. An accurate prediction of the reservoir quality in sandstones forms the basis of an accurate porosity and permeability prediction ahead of drilling wells in petroleum exploration, development, or production.