--> ABSTRACT: Unconformities: Key to Hydrocarbon Migration and Entrapment, by Glenn S. Visher; #91039 (2010)

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Unconformities: Key to Hydrocarbon Migration and Entrapment

Glenn S. Visher

Analysis of hydrocarbon distribution in the Mid-Continent area and throughout the world, indicates that unconformities control the depositional history, the reservoir development pattern, migration pathways, and hydrocarbon-seal development. Anticlinal and fault traps are most commonly the site for accumulation of hydrocarbons, but many structures either do not contain hydrocarbons or contain only minor accumulations. Traps not closely associated with an unconformity surface cannot segregate hydrocarbons from the many thousands of pore volumes of fluid that migrate along the unconformity surface from the compacting source rocks in the basin center.

Unconformities caused by periodic changes in sea level are readily observed from seismic and log sections and facies models. Unconformities below the Simpson, Woodford, Morrowan, and the Wolfcampian granite wash are the controls for the accumulation of hydrocarbons. Patterns of truncation, onlap, topography, and structural history of these surfaces is the key to discovering new hydrocarbon accumulations in the Mid-Continent.

Location of subtle traps associated with these unconformities has not been widely used in the Mid-Continent. Detecting hydrocarbon accumulations requires isopach mapping of intervals between event markers, both below and above the unconformity surface. These isopach maps provide information on timing and pattern of the structural history, topographic control for onlapping reservoir units, points for fluid migration into overlying onlapping sequences, and truncation of underlying reservoir units. Study of these maps indicates areas for hydrocarbon accumulations in various stratigraphic units, including the Simpson, Hunton, Misener, Mississippian carbonates, Morrowan, and a succession of onlapping Atokan and Desmoinesian rocks and in Wolfcampian granite wash.

AAPG Search and Discovery Article #91039©1987 AAPG Mid-Continent Section Meeting, Tulsa, Oklahoma, September 27-29, 1987.