Lopatin Modeling as Tool for Regional Basin Analysis

Janell D. Edman, Janet K. Pitman

Lopatin modeling is a powerful tool for understanding hydrocarbon maturation within the context of basin evolution. Commonly, neither the thermal gradient nor the magnitude and timing of erosional events within a basin are precisely known. Using a series of Lopatin models constrained by measured maturation data, we can delineate variations in gradient through time, estimate the extent and magnitude of erosional events, and determine the sensitivity of maturation to changes in these parameters.

This approach was applied to Upper Cretaceous units in the Uinta and Green River basins. For example, in the Uinta basin, using the present gradient of 1.6°F/100 ft requires about 3,000 ft of intra-Tertiary erosion to match the measured vitrinite reflectance. This amount of erosion is significantly greater than 1,700 ft extrapolated from the vitrinite data. The model incorporating 1,700 feet of erosion requires a gradient of 1.8°F/100 ft through the middle Miocene, followed by the slightly cooler present gradient to match the data. By systematically varying temperature gradient and burial history, a best-fit model was derived.

A series of Lopatin models for both basins shows source rock maturity was not affected by erosion during the Late Cretaceous because these units had not been deeply buried. Active generation did not begin until the middle to late Tertiary, when sediments were near maximum burial depths. This period was followed by an interval of passive generation related to widespread late Tertiary erosion. Thus, sedimentary burial exerted the dominant control over maturation in Upper Cretaceous rocks.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.