N201 Depositional Systems, Sequence Stratigraphy and Diagenesis of Carbonate Rocks

Despite hosting around 60% of the world’s hydrocarbon reserves carbonate rocks and reservoirs are often viewed as complex and unpredictable and their study requires additional skills to those needed to understand clastic systems. The course covers the basic information that is needed to understand facies models and diagenetic environments. Sequence stratigraphy is a conceptual and predictive framework that enables geoscientists to improve their understanding of the location and likely quality of carbonate reservoirs.

The course will be divided into four parts:

Part 1 will introduce the building blocks of carbonate rocks; carbonate minerals, carbonate grain types, rock textures, and the different environments in which they form. Carbonate depositional processes will be studied using case studies from present-day humid and arid sedimentary environments. Facies models will be developed that aid in the prediction of potential reservoir facies. Practical work on a range of carbonate facies will be integrated with the lectures.

Part 2 focuses on diagenetic changes such as recrystallisation and dissolution that affect carbonate sediments from the time of their deposition through to burial and hydrocarbon charge. These changes may fundamentally alter the porosity and permeability of limestones and dolomites and therefore have an important, sometimes overriding, control on reservoir quality. Images of various diagenetic textures and structures will be studied from SE Asian examples and their porosity and permeability discussed.

Part 3 examines the basin-scale controls on the accumulation of strata and introduces the concepts of carbonate sequence stratigraphy and the tectonic controls on the on formation of different types of platforms. Sequence stratigraphic building blocks; systems tracts, parasequences and depositional sequences are studied together with the significant surfaces that divide up stratigraphies; marine flooding surfaces and sequence boundaries (unconformities). Tectonic controls on the formation of carbonate platforms are significant in SE Asia and Bosences recent genetic classification of platform types will be introduced.

Part 4 will integrate the skills learnt in parts 1 to 3 to achieve an understanding of carbonate reservoirs. These are often said to form three main types; those controlled by the occurrence of particular sedimentary facies, those controlled by particular diagenetic fabrics, and those
controlled by fractures. The different types of pore systems, their origin and their permeabilities will be discussed. Case studies of different reservoir types will be studied, using examples from SE Asia as well the different schemes that are used to classify different carbonate reservoir rock types.

Planned Agenda

Part 1 - Day 1
1. Introduction to carbonate depositional systems, carbonate minerals, carbonate rocks
and their classification.
2. Skeletal grain production and reef-rimmed, attached platforms.
3. Non-skeletal grain production and facies models for rimmed carbonate shelves.
4. Carbonate ramps; arid-climate, peritidal carbonates and ramp facies models.

Part 2 - Day 2
5. Principles of carbonate sequence stratigraphy.
6. Sequence stratigraphy of rimmed carbonate shelves and isolated platforms.
7. Sequence stratigraphy of mixed carbonate-evaporite and carbonate-clastic systems.
8. Sequence stratigraphy of carbonate ramps.
9. Numerical forward modelling of carbonate systems.

Part 3 - Day 3
10. Early diagenesis of limestones; mineralogy, textures and porosity evolution.
11. Dolomites and dolomitization.
12. Late stage diagenesis of limestones and dolomites.
13. Environments and trends in diagenesis.
14. Recognition of different porosity types and their origin and significance.

Part 4 - Day 4
15. Application of sequence stratigraphy to Tertiary and Mesozoic successions, including
SE Asia.
16. Tectonic and basin-scale controls on the occurrence and nature of carbonate
platforms with examples from SE Asia.
17. Sequence stratigraphic analysis of seismic and outcrop datasets.

Part 4 - Day 5
18. Carbonate pore system types and carbonate reservoir rock types.
19. Carbonate reservoirs; depositional versus diagenetic versus structural controls.
20. Carbonates through time; the present is not always the key to the past.