Entrapment Potential Maps

Abstract

The trapping of hydrocarbons occurs in subsurface geologic features when the orientation of forces is such that the oil and gas are held in place and cannot escape in any direction. One classification scheme, devised by Meissner (1984) and illustrated in Figure 11.1, proposes a three end-member system constituting a triangle. The three end-members in the scheme occupy positions at its apices: structural traps (lower left), stratigraphic traps (lower right), and hydrodynamic traps (top center). Structural traps are geometrically “closed” on all four sides (two sides in cross section) and the hydrocarbon-water contacts are horizontal. The reservoirs are hydrostatic. The influence of the structural component decreases upward along the left leg of the triangle. The first dynamic pool is an accumulation trapped off the crest of the structure, held in a downflank position, with a dipping oil-water contact. The next feature is a monocline, also nonclosed with a tilted oil-water contact. The last pool on this leg, close to the hydrodynamic end-member position, is essentially a slug of oil localized at the bottom of a synclinal trough, held there by convergent downdip flow. No one, to our knowledge, has ever described an oil accumulation of this kind, but theory and hydromechanics suggest that it could exist under proper hydrodynamic conditions.