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Stratigraphic Traps: Quantitative Approach Based upon a Producing Field Database

Gerard, Jean 1
1 Discplinas Geologicas, Repsol Exploracion SA, Madrid, Spain.

Stratigraphic traps are hydrocarbon accumulations independent of structural or fault closure. The factors controlling the stratigrahic traps involve facies change, depositional pinch-out, erosional truncation, hydrodynamics, diagenesis, or other factors or a combination.

The prediction of stratigraphic traps relies on a good undestanding of complex geological settings. Modern exploration tools such as 3D seismic data generally provide fair imaging of the stratigraphy. Nevertheless, not only the search for Direct Amplitude Indicator (DHI) can be applied to identify stratigraphic traps, detailed sequence stratigraphy analysis calibrated by core data and biostratigraphical results must be performed to predict facies variations and geometric architecture of the reservoir-prone section and seal-prone section respectively.

The efficiency of bottom seal, lateral seal and top seal is the driving mechanism of the success as any failure in the seal capacity will alter hydrocarbon (HC) accumulation.

A series of queries performed on a non-exclusive database provided a statistical evaluation of the relationships between geometric parameters of the traps and HC types. Geometrical aspects such as the dip of the top of the reservoir and the physical conditions as HC density and pressure in bottomhole conditions are controlling the seal integrity. Most HC producing fields having some stratigraphic component have a very low relief with a P50 value close to 2 degrees. HC producing stratigraphic traps with dip larger than 12 degrees do not exist. Porosity and permeability of the reservoir control recovery factors and therefore contribute to economic calculations. Assessment of stratigraphic traps is best achieved when supported by good understanding of the geology, statistical analysis of geometric parameters and reality check with possible analogs from the database.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009