The Concept of Entrapment: Towards Expanding the Paradigm

Arif I. Alkalali
Saudi Aramco
[email protected]

The current conceptualization and approach of exploration sets a specific timing for hydro-carbon migration and entrapment and certain geometries for accumulation. The simplest of those is the anticlinal four-way dip closure in which the lighter hydrocarbons migrate up-dip due to their density contrast with the water to arrive to a pseudo-stagnant state. Such an understanding of a simple fluid behavior led to the discovery of huge reserves worldwide. Although successful, limiting the migration and entrapment model to only such physical conditions can be limiting to our hydrocarbon-finding ability. An expansion of the migra-tion and entrapment model that recognizes the dynamic behavior of hydrocarbons than just the pseudo-stagnant model can define new exploration opportunities. The model is sup-ported by analyzed discovery fields, laws of physics, physical and numerical models. The new paradigm states that: (1) hydrocarbons are in continuous movement during basin evo-lution; (2) entrapment is a phase of the hydrocarbon movement; (3) massive volumes of ex-pelled hydrocarbons continue to move on a geological time scale; (4) perfect seals are not in line with known behavior of even the tightest rock over a geological time scale; and (5) hydrocarbons will become stagnant only in a site of subsurface hydrocarbon energy min-ima, which is rarely sustained during the life of an accumulation. The above paradigms de-fine a new set of traps and real examples supported by physical and numerical models are presented. A set of mapping techniques to identify those traps is proposed. The Arabian Platform tectonic and depositional history, and hydrodynamic conditions form a hydrocar-bon-prospective region to apply such new concepts and techniques.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain