--> Petrophysical Constraints in the Evaluation of Hydrodynamic and Capillary Pore-Throat Traps, by S. M. Goolsby, E. B. Coalson, and M. H. Franklin; #90986 (1994).

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Abstract: Petrophysical Constraints in the Evaluation of Hydrodynamic and Capillary Pore-Throat Traps

Steven M. Goolsby, Edward B. Coalson, Mark H. Franklin

Capillary pore-throat changes and hydrodynamic conditions have been recognized as subtle trapping mechanisms for large hydrocarbon accumulations since the 1950s, but the relative importance of the two remains controversial. Although distinct and independent physical constraints are necessary to explain oil accumulations under these contrasting models, both are often used by different workers to explain a particular accumulation. Conversely, both mechanisms are rarely cited together for a single accumulation.

Careful examination of the fluid relationships and of the petrophysical properties of pore systems in the vicinity of an accumulation can usually clarify which mechanism is responsible for trapping. Identification of the capillary transition and waste zones using integrated rock and geophysical log data can determine the relative importance of pore-throat changes and hydrodynamic flow to an accumulation. The position of these zones is different for each of these two trapping models. In hydrodynamically trapped accumulations, the transition and waste zones are tilted off structure along with the productive portion of the accumulation. In contrast, pore-throat traps usually exhibit an updip waste zone and a down-dip transition zone. Upper Valley field in Utah and Weyburn field in Saskat hewan can be employed as examples of how to use petrophysical constraints to determine which of these trapping mechanisms is responsible for specific large hydrocarbon accumulations. Resolving the relative importance of these two mechanisms can have important implications in the development of a particular field or in further exploration in a basin.

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