|TOWARDS AN EARTH MODEL: INTEGRATING STRATIGRAPHY AND TECHNOLOGY|
|Field Developments and Case Studies|
1Neftex Petroleum Consultants Ltd
Information technology advances in the last 5 years, coupled with the power of sequence stratigraphic synthesis, means that it is now possible to build a global Earth Model - a 4D model of the Phanerozoic stratigraphic evolution of the planet.
Neftex continues to extract and analyse the vast global geoscience data resource from published and public sources (requesting permission where necessary) and applies sequence stratigraphic techniques to better understand the geological evolution of the Earth. The Earth Model provides consistent risk reduction and value creation through application of global standards to a global framework for upstream evaluations throughout the value chain. Intriguing applications also exist in other sectors such as groundwater, mining and finance.
The consistent global analyses of tens of thousands of pieces of geoscience data from almost every basin in the world strongly suggests that we can identify the “3rd order” sequence stratigraphy of the Phanerozoic and that the causal mechanism is eustasy. The resulting Earth Model of over 100 depositional sequences enables accurate global stratigraphic mapping. As a result Neftex has constructed many hundreds of chronostratigraphic charts and structural cross sections, thousands of gross depositional environment maps in GIS, thousands of interpreted digital outcrops and well logs, and a database of over a million items of source rock data, all integrated by use of this common global sequence stratigraphic Earth Model.
|THE WORK BUILDS ON CLASSIC SEQUENCE STRATIGRAPHIC REASONING DEVELOPED IN THE LAST 30 YEARS:|
- Sequence stratigraphy better explains the geometric relationships of sediment packages. Because the technique is based on understanding the temporal and spatial relationship of sediments, we can better understand if, for example, they are physically connected (useful for estimating likely reservoir volume and well connectivity). This is a much more accurate approach than simple, and potentially very misleading, lithostratigraphic correlation;
- It is a very effective means of combining datasets (e.g. biostratigraphy, sedimentology, wireline logs, seismic, etc) within an integrated global framework;
- It is a more accurate means of prediction away from data control points. Sequence stratigraphy better predicts what facies may be expected up and down systems tract and along strike. The global presence of reservoirs, source rocks and seals may thus be predicted more accurately from relatively sparse datasets.
The above are valid benefits regardless if of whether or not eustasy is the causal mechanism. If a eustatic model can be applied, then other, powerful, benefits also accrue:
- A global framework for detailed and precise correlation, mapping and isopaching exists;
- Use of global analogues & generic play concepts is possible.
|OUR BASIC METHODOLOGY (SEE ALSO SHARLAND ET AL., 2001; 2004; SIMMONS ET AL., 2007) IS:|
- Identify Maximum Flooding Surfaces in platform settings and Maximum Regression Surfaces and Sequence Boundaries/Correlative Conformities in basinal settings within outcrop, wireline log and seismic data through facies characterization and stratigraphic analyses (Figure 1);
Figure 1: Distillation of sequence stratigraphic concepts.
- Global correlation of these surfaces through use of biostratigraphic and chemostratigraphic data with an appreciation of accommodation space and the correlation issues between different fossil groups;
- Use these biostratigraphically-validated surfaces as the basis for drawing an intersecting global grid of plate-scale chronostratigraphic charts;
- Use this grid of chronostratigraphic charts tied to all the well and outcrop data to assist the mapping of global facies distributions at the key stratal surfaces above, and including an appreciation of the vertical and lateral shifts in sea-level, the duration of lowstands and the recognition of the (sometimes very major) influence of local tectonics and sediment supply.
- Facies maps are then turned into Play Fairway polygons for reservoir, seal and source.
Using the latest GIS mapping and 3D modeling technology these global facies maps can then be visualized in 2D and 3D environments, and then in 4D by use of GIS based plate reconstruction applications.
Sharland, P.R., Archer, R., Casey, D.M., Davies, R.B., Hall, S.H., Heward, A.P., Horbury, A.D., & Simmons, M.D. 2001. Arabian Plate Sequence Stratigraphy, GeoArabia Special Publication 2, 371pp.
Sharland, P.R., Casey, D.M., Davies, R.B., Simmons, M.D. & Sutcliffe, O.E. 2004. Arabian Plate Sequence Stratigraphy – revisions to SP2, GeoArabia, 9, 199-214.
Simmons, M.D., Sharland, P.R., Casey, D.M., Davies, R.B. & Sutcliffe, O.E. 2007. Arabian Plate sequence stratigraphy: Potential implications for global chronostratigraphy. GeoArabia, 12, 101-130.