--> Abstract: Measured and Modeled Vitrinite Reflectance-Comparisons in Diverse Basins, by V. F. Nuccio and J. W. Schmoker; #90987 (1993).

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NUCCIO, VITO F., and JAMES W. SCHMOKER, U. S. Geological Survey, Denver, CO

ABSTRACT: Measured and Modeled Vitrinite Reflectance-Comparisons in Diverse Basins

Thermal maturity data and burial history reconstructions are commonly combined to assess the maturation of kerogen and the timing of petroleum generation, migration, and preservation. Other applications have come to include modeling of basin development, thermal regimes, heat transport, reservoir diagenesis, and porosity evolution. Laboratory measurements of thermal maturity include vitrinite reflectance, bitumen reflectance, thermal alteration index, and data drawn from Rock-Eval pyrolysis. These measurements are commonly correlated to one another and expressed as a vitrinite reflectance equivalent. Kinetic and time-temperature (TTI) methods have also been developed that calculate equivalent vitrinite reflectance.

The present study compares equivalent vitrinite reflectance (R<oe>) as determined from laboratory measurements with, R<oe> from both kinetic and TTI models and investigates their internal consistency using examples from basins of diverse ages and geologic histories. Cases presented include Paleozoic rocks of the Anadarko and Williston Basins, Jurassic strata of the eastern Gulf Coast, Cretaceous rocks of the Piceance and Wind River Basins, and Tertiary formations of the Uinta Basin.

For the Upper Devonian-Lower Mississippian Woodford Shale between 5,000 and 25,000 ft (1,500 and 7,600 m) in the Anadarko Basin of Texas and Oklahoma, R<oe> as determined from TTI is 1.3 to 2.0 times higher than both measured and kinetic-modeled R<oe>. For example, for the Woodford at a depth of 21,500 ft (6,553 m), R<oe> (measured) is 3.0 percent, R<oe> (kinetic) is 2.70 percent, and R<oe> (TTI) is 5.3 percent. For the Upper Jurassic Norphlet Formation of southwestern Alabama and vicinity at depths of 10,000 to 22,000 ft (3,050 to 6,700 m), R<oe> as determined from TTI is 1.3 to 1.7 times higher than both measured and kinetic-modeled R<oe>. For example, at Hatter's Pond Field at a depth of about 18,400 ft (5,600 m), R<oe> (measured) is .62 percent, R<oe> (kinetic) is 1.68 percent, and R<oe> (TTI) is 2.73 percent As a third example, for the Upper Cretaceous Mesaverde Formation in the Wind River Basin of Wyoming, R<oe> as determined from TTI is 1.4 to 1.5 times higher than both measured and kinetic-modeled R<oe>. For the Mesaverde at a depth of 13,000 ft (3,960 m) in the northwestern part of the basin, R<oe> (measured) is 1.10 percent, R<oe> (kinetic) is 1.10 percent, and R<oe> (TTI) is 1.60 percent.

For all of our examples, thermal and burial histories are fairly well constrained. TTI modeling consistently over-predicts R<oe> as determined from laboratory measurements, but R<oe> trends determined from kinetic modeling and laboratory measurements are generally in excellent agreement. We conclude, therefore, that in areas where burial and thermal histories are not well constrained, it is reasonable to vary parameters such as amounts of erosion, heat-transport, paleogeothermal gradients, surface temperatures, etc., until kinetic-modeled R<oe> and measured R<oe> trends are brought into agreement.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.