An Overview of Carbonate Diagenesis: The Good, The Bad, and The Ugly of Carbonate Reservoir Quality
Diagenesis includes all chemical, physical and biological changes, modifications or transformations undergone by a sediment after its deposition and during and after its lithification (AGI Glossary of Geology), exclusive of metamorphism. Carbonate rocks and sediments are especially susceptible to post-depositional modifications because of the high chemical reactivity of carbonate minerals; these carbonate minerals react quickly with natural waters in order to bring the water into equilibrium with the host carbonate sediments and rocks (Moore 1989). These rock-water interactions can have a dramatic effect on the original (depositional) reservoir quality framework of a sediment, and can either create, modify, or completely destroy reservoir quality. Given that these alterations can occur at any time during the history of the sediment, understanding and predicting carbonate diagenesis and its impact on reservoir quality can be a very challenging - and at times frustrating! - process.
While the full gamut of carbonate diagenetic processes is extensive, a simplified list of the most commonly encountered processes includes: cementation, dissolution, dolomitization, compaction (including pressure solution and stylolitization), fracturing, and the in situ growth of other minerals in the sediment. These processes can be considered within a context of diagenetic environments, including the marine environment, the mixing zone, the meteoric environment, and the burial environment. A consideration of the typical conditions, processes and products for each of these diagenetic environments provides a method for both understanding and predicting carbonate diagenesis.
The relationship between reservoir quality and diagenesis is complex and variable, and at times the various diagenetic processes work in complementary and overlapping ways. For example, movement of undersaturated water through a sediment may partially dissolve the sediment to create or enhance porosity; as dissolution continues, however, waters may become saturated to the point where they cement porosity in adjacent sediments, to produce a tightly cemented carbonate rock with abundant moldic porosity but little permeability. Likewise dolomitization may occlude, redistribute, create or enhance porosity, based on a number of different factors.
This workshop provides an in-depth overview of the nature and extent of common diagenetic alterations in carbonates and their impact on reservoir quality; it then uses a series of case studies to illustrate how the principles described in this workshop can be applied to understand and predict reservoir quality in several outcrop and subsurface examples.
Upon completion of the course, participants will be able to:
- identify common diagenetic products in carbonate rocks and sediments
- understand the processes that gave rise to these products
- predict the likely location and effect of diagenesis in the subsurface
- appreciate the role that diagenesis plays in producing final reservoir quality
Diagenesis in Carbonate Rocks and Sediments – what is it, and why should you care?
Aspects of Diagenesis: Recognition of Processes and Products
- Compaction and Pressure Solution
- Fracturing and Others
Diagenesis in Time and Space - the Importance of Diagenetic Environments
Implications for Reservoir Quality
Case History #1: Dolomitization in Middle Eastern Carbonate Rocks
Case History #2: Introduction to Karst Systems and Reservoirs
Case History #3: An Introduction to Microporosity in Middle Eastern Carbonate Rocks
The course is designed for geoscientists and engineers looking to enhance their understanding of and ability to predict carbonate diagenesis.
Some knowledge of carbonates and the main challenges of reservoir quality prediction and modeling in carbonates would be helpful.
- Longman, M. W., 1980, Carbonate diagenetic textures from nearsurface diagenetic environments: Amer. Assoc. Petroleum Geologists Bull., v. 64, p. 461-487.
- Tucker, M. E. and Wright, V. P., 1990, Carbonate sedimentology: Blackwell Scientific, Oxford, 482 pp.
About the Instructor
Dave L. Cantrell has over 35 years of worldwide geologic industrial and academic experience. He graduated from the University of Tennessee with an MSc in Geology in 1982, and from the University of Manchester with a PhD in Geology in 2004. Dave began his industry career in 1982 with Exxon where he conducted numerous reservoir characterization and geological modeling studies on reservoirs in the Middle East; the Permian, Powder River, Williston, and Gulf of Mexico Basins of the USA; and the Maracaibo and Barinas Basins of Venezuela; among others. After moving to Saudi Arabia in 1997, he conducted studies on several large carbonate fields there, and lead geologic R&D for Saudi Aramco from 2000- 2008; he also served as a professor and Associate Director for the College of Petroleum Engineering & Geosciences at King Fahd Petroleum & Minerals (KFUPM) from 2015-2017. He is an AAPG Certified Petroleum Geologist, a Fellow of the Geological Society of London, and an adjunct professor at Stanford University; he has published over 40 articles in peer-reviewed journals, and holds one patent.