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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 921

Last Page: 921

Title: Overview of Seals for Hydrocarbons: ABSTRACT

Author(s): Marlan W. Downey

Article Type: Meeting abstract


Seals for hydrocarbons need to be analyzed and described at two differing scales. A micro view of the rock matrix, pore structure, and fluid content of the seal surface provides quantitative information about the capacity of the seal to impede hydrocarbon movement at a specific measured point. Such micro information often can be accurately measured, but can rarely be extrapolated to describe the overall (mega) sealing capacity of a large hydrocarbon trap.

Efforts have been made over the years to describe the lateral variability of seals for hydrocarbon accumulations. One of the best features of the simple anticlinal structure is that it generally provides sequential sealing surfaces. Top-seal surfaces may be expected to have relatively little lateral variability (at least on the scale of an individual anticline). Faulted structures, in contrast, require not only a top seal, stable in lithology over the trap area, but require juxtaposition of the hydrocarbon-bearing interval against a sealing lithology at the fault plane surface. Large hydrocarbon columns become almost impossible to seal if the trapping configuration requires multiple faults with throws that vary along the individual faults.

Stratigraphic traps for hydrocarbons typically require a top seal, bottom seal, and an updip lateral seal. In addition, the transition from reservoir to seal must be very rapid or the hydrocarbon accumulation will largely occupy a "waste-zone"--not quite a reservoir, hardly a seal.

Regionally, it can be shown that hydrocarbons are preferentially distributed under major roofing seals. These major sealing units are characterized by broad extent, by laterally stable character, and commonly by ductile lithologies. Where these regional seals are above significant source rocks and reservoirs, they largely control the emplacement of hydrocarbon accumulations.

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Copyright 1997 American Association of Petroleum Geologists