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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 63 (1979)

Issue: 8. (August)

First Page: 1428

Last Page: 1428

Title: Design and Function of Oil and Gas Traps: ABSTRACT

Author(s): W. H. Roberts, III

Article Type: Meeting abstract


Oil and gas are found in traps. If we can understand what is going on in traps, we should be able to look back along the migration trail with special insight as to what has happened. That insight could even extend all the way back to the "source."

Traps are the most logical places for hydrocarbon mixtures to be put together as distinct oil and gas fluids. It follows that traps are not just passive receivers or containers of hydrocarbon mixtures put together elsewhere. Effective oil and gas traps of different well-known styles have a very important feature in common: structurally and stratigraphically, they are designed to discharge waters from depth. Thus they function as active focal mechanisms to gather and process feedstock waters carrying hydrocarbons and other organic materials. It is a forced-draft system. The concept adds an exciting new dimension to the anticlinal theory. It honors all factual observations around oil and gas deposits.

Very simply, the most important function of a trap is to leak water while retaining hydrocarbons. The water can leak because the enclosing membranes and cover are water-soaked, like a wick. The hydrocarbons and other organic materials are separated from the waters as they pass through the trap. The separation is caused by abrupt changes in pressure, temperature, and possibly salinity--those changes being related to the basic change in direction of feedstock (water) movement from lateral to upward. Coalescence of hydrocarbons makes bubbles or globules which cannot move so easily as water. The ultimate composition of a trapped hydrocarbon mixture depends on the respective residence times of the various components of that mixture which in turn depend on (1) what the water carries to the rap, (2) what the trap retains, and (3) the pore-volume exchange rate.

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