About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

CSPG Special Publications


Facts and Principles of World Petroleum Occurrence — Memoir 6, 1980
Pages 998-999
Symposium Abstracts

Modern Concepts in Sandstone Diagenesis: Abstract

Volkmar Schmidt1, David A. McDonald2

Established concepts in sandstone diagenesis are changing and new concepts are being developed as the result of new or improved methods of analysis and interpretation. Advanced methods are now routinely used in the visual analysis of sandstones and pore casts, and in the analysis of the crystallography and chemical or isotopic composition of sandstone constituents. Interpretive methods that originally were developed in the study of carbonate diagenesis proved to be extremely useful in the petrologic interpretation of sandstones. Changes of composition, fabric, porosity and pore geometry can commonly be assigned to the three major realms of sandstone diagenesis:

  1. eodiagenesis (pre-burial);

  2. mesodiagenesis (during burial); and

  3. telodiagenesis (post-burial).

Significant improvements have also been achieved in the ability to differentiate between primary and secondary sandstone porosity, and in tracing the thermal history and the history of fluid migration and compaction in sandstones and their host sediments.

Mesodiagenesis is the most important realm for sandstone diagenesis in relation to the exploration and production of conventional hydrocarbons. Mesodiagenesis is not simply an irreversible path of mineral stabilization and porosity loss dependent mainly on the factors of time, temperature, overburden pressure, and the mineralogical maturity of sandstone constituents. The course of mesogenetic sandstone alteration is often strongly influenced by additional factors such as:

  1. geopressures;

  2. carbonate content;

  3. the abundance, type, and degree of maturation of associated organic matter;

  4. chemical composition of pore fluids;

  5. flow rate and migration path of pore fluids;

  6. transfer of dissolved matter between sandstones and intercalated host sediments;

  7. sandstone fabric;

  8. pore volume and pore geometry; and

  9. presence of hydrocarbons as pore filling media.

Large volumes of mesogenetic porosity are frequently created in sandstone at depth. This significantly increases the depth range of reservoir-grade porosity in sandstones. Dissolution of carbonate constituents is prominent among the mesogenetic processes that create sandstone porosity. The chief cause for this decarbonatization appears to be the carbon dioxide that is generated during the maturation of organic matter.

Mesogenetic loss of sandstone porosity occurs mainly through:

  1. mechanical compaction;

  2. chemical compaction; and

  3. authigenic cementation mainly by silica, carbonate, clay minerals and zeolites.

Zones of diagenetic textural maturity of sandstones can be defined on the basis of porosity loss and are mappable in the subsurface.

Chemical compaction is commonly but not invariably associated with reprecipitation of the dissolved constituents. In most sandstones the amount of mesogenetic pore-cement exceeds the amount of constituents that were dissolved during chemical compaction. This indicates a net addition of mineral matter in sandstones.

Minerals that are unstable under prevailing physicochemical conditions may be eliminated by dissolution, replacement or crystallographic reorganization. All common sandstone constituents, including quartz, can become unstable during mesodiagenesis and may be replaced by another mineral, or be dissolved.

Physico-chemical conditions in the subsurface vary greatly through time in individual sandstone units. This is reflected in the complex and variable history of mesogenetic sandstone diagenesis. The reservoir quality of sandstones can only be predicted if the status of diagenetic alteration itself can be foretold. Accurate prediction of the effects of mesodiagenesis in sandstones is still virtually impossible. However, the success ratio of qualitative predictions of the diagenetic status of sandstone reservoirs has been significantly increased through the application of modern petrologic concepts.

Acknowledgments and Associated Footnotes

1 Petro-Canada, Calgary, Alberta

2 Petro-Canada, Calgary, Alberta

Copyright © 2009 by the Canadian Society of Petroleum Geologists