Abstract: Hydrocarbon Generation, Migration, and Entrapment in Thrust Belts: Effects of Geometry, Kinematics, and Mechanics

Steven E. Boyer

Mechanical principles, acting through constraints imposed by stratigraphy and basin morphology, control the geometry and kinematic evolution of thrust belts. The relationship between geometry (trap) and kinematics (timing of structural development and hydrocarbon generation) in turn controls the distribution of hydrocarbon-bearing structures internal and external to thrust belts. Internal traps are usually fault-related folds. External foreland traps are a combination of structural and stratigraphic and are often related to flexure and failure of the foreland crust induced by tectonic loading.

Spatial relations between source and potential trap determine whether timing is important to charging of reservoirs. Relative timing of trap formation and source maturation is usually of minor importance in the case of a hanging wall source and reservoir but is critical for the charging of hanging wall structures by footwall sources. If generation occurs too early, no internal traps are in place, and hydrocarbons may migrate into the foreland basin, rather than into hanging wall structures. If generation is too late, hanging wall cutoffs have moved well beyond mature footwall source rocks, and pathways are less conducive to migration.

Relative thrust timing also affects the charging of reservoirs. Most published models of hydrocarbon generation in thrust belts have relied on hinterland-to-foreland, "piggy-back", thrust sequence. However, a re-examination of stratigraphic and geochronologic data and structural analysis, which incorporates down-structure views and kinematic restorations, indicates that synchronous and "out-of-sequence" imbrications are the norm. To be of any value, modeling of hydrocarbon systems in thrust belts must incorporate these kinematic constraints.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994