--> ABSTRACT: Permeability Structure of a Highly Heterogeneous Transgressive-Marine Complex: Tocito Sandstone, New Mexico, by M. L. Lambert, P. S. Mozley, and G. W. Riley; #91019 (1996)

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Permeability Structure of a Highly Heterogeneous Transgressive-Marine Complex: Tocito Sandstone, New Mexico

M. L. Lambert, P. S. Mozley, and G. W. Riley

The Tocito Sandstone Member of the Mancos Shale is an Upper Cretaceous shallow-marine sandstone and mudrock complex deposited along the western margin of the Western Interior seaway. The Tocito is a major hydrocarbon producer in the San Juan Basin (approximately 117 million barrels of oil and 79 billion cubic feet of gas). Because of reservoir heterogeneity, ultimate Tocito oil recovery factors are low, generally between 10 and 20 percent.

To enhance understanding of permeability heterogeneity in the Tocito, we have undertaken a detailed surface and subsurface investigation. A total of 2,697 permeability measurements have been made using minipermeameters. Permeability variation within the Tocito is controlled by two principal factors: lithofacies and buriall'diagenetic history. Coarser grained and better sorted lithofacies have the highest permeability. The permeability values from outcrop and shallow subsurface cores are dramatically higher than those from deep subsurface cores. This is due to dissolution of grains and calcite cement, and decompaction that preferentially affected the outcrop and shallow subsurface. Correlation lengths for permeability values along horizontal transects are typically less than 3 m, where s those for vertical transects are usually less than 0.6 m. These data suggest that small grid block sizes should be used during reservoir simulations if the investigator wishes to accurately capture the reservoir heterogeneity.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California