ABSTRACT: Upstream Source Systems and Downstream Trap Systems
In this paper, I try to apply common sense to the relationship of petroleum sources and accumulations by looking at some functional aspects of fluid transfer between the two. The actual physical linkage between petroleum sources and geochemically correlated petroleum accumulations is very uncertain. Basic geology, hydrology, and fluid mechanics may help.
The terms "upstream" and "downstream" are useful in referring to sources and reservoirs in a basin-wide, three-dimensional fluid continuum; however, one should avoid the ambiguous term "fluid." It is critically important to know specifically what is deemed to be moving, from where to where, and why. In the porous media of typical petroliferous basins, water is estimated to be the dominant fluid by five to ten orders of magnitude. In such an essentially aqueous continuum, the upstream and downstream positions are defined by the level of energy potential in relation to the earth's gravitational field. Gas and oil accumulations usually are found downstream. In such a water-dominant, water-soaked system, the independent natural movement of gas or oil via discrete channels or conduits seem unlikely.
Field evidence of the association of gas and oil traps with downstream hydrologic situations occurs both at the surface and in the subsurface. The data of interest include all geological, geochemical, and geophysical information obtained at many different levels, from satellite imagery to deep surface. Mid-continent examples of these observations include the Anadarko basin at
large and specific references to such fields as Hugoton, Healdton, Cement, and Velma.
AAPG Search and Discovery Article #90991©1993 AAPG Mid-Continent Section Meeting, Amarillo, Texas, October 10-12, 1993.