Unconformities: key to hydrocarbon migration and entrapment

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.