PetroStruc

Sequence Stratigraphy

 

Sequence stratigraphy studies changes in depositional trends (i.e. progradation, retrogradation, aggradation, erosion) and the resulting stratal stacking patterns through time. These changes are controlled by variation in the balance between accommodation creation or destruction and sedimentation rate (Weimer and Posamentier, 1993; Emery and Myers, 1996; Posamentier and Allen 1999, Catuneanu, 2002, 2006; Catuneanu ey al., 2009; Martins-Neto and Catuneanu, 2010). Sequence stratigraphy is a powerful exploration tool as it characterises the spatial and temporal distribution of depositional systems, allowing more reliable prediction of reservoir, source and seal facies distibution and properties.

 

Classic sequence stratigraphy was developed in the context of passive margin settings, which are tectonically stable areas where accommodation is primarily controlled by global eustatic sea-level variations on a background of longer term thermal subsidence (Vail et al., 1977; Posamentier and Vail, 1988). More recently sequence stratigraphic studies have emphasised the role of tectonism in particular, as well as climate, as major external forcing mechanisms (e.g. Martins-Neto and Catuneanu, 2010). However, despite the fundamental differences in sequence development in tectonically stable versus active basins, many studies are performed applying the passive margin model. Ignoring the effects of tectonism can lead to major errors in the sequence stratigraphic model, and hence, poor characterisation of petroleum systems, plays and prospects.

 

Structural geology and sequence stratigraphy have a intimate complimentary relationship where each discipline helps the understanding of the other to refine the geological evolution of a region. A pragmatic approach that integrates structural geology and sequence startigraphic observations is therefore critical in tectonically active settings (e.g. Australian and SE Asian basins). Robust sequence stratigraphic interpretation also involves the integration of some, if not all, of the following data sources:

 

• Well log/core - EOD, stacking patterns, coarsening-fining trends.

• Seismic data - terminations & truncations, shelf edge trajectories, seismic facies mapping, surface attribute extractions.

• Biostratigraphy - EOD, age.

• Palaeogeography