Diagenetic Controls on Petrophysical Properties of Dakota Sandstone, West Lindrith Field, Rio Arriba County, New Mexico

Stan P. Franklin, Thomas T. Tieh

The Cretaceous Dakota Sandstone at West Lindrith field on the eastern margin of the San Juan basin consists of a series of coarsening-upward, shallow marine sandstones interstratified with marine shales. Petrographic and SEM analyses indicate that the sandstones are very fine to medium-grained litharenites that have been pervasively altered by the diagenetic processes of compaction, authigenesis, and dissolution.

The course of diagenesis varied spatially and temporally within the sandstones because of variations in primary composition and texture related to depositional environment. Diagenetic alterations have profoundly affected the development of secondary rock properties such as porosity, permeability, and water saturation. Each of the resulting "diagenetic facies" contains a unique authigenic mineral assemblage and a dominant secondary porosity type that reflect a specific sequence of diagenetic alterations.

Q-mode multivariate factor analysis of petrographic data has been used to delineate three compositional end members and to relate depositional environment, diagenesis, and reservoir quality. End member 1 sandstones are clean, quartzose, current-deposited sands that are silica cemented and contain relatively high porosity, permeability, and low water saturation. End member 2 sandstones, adjacent to interbedded shales, are tightly carbonate cemented and have little or no reservoir potential. End member 3 sandstones are shaly, low-energy deposits, fine to very fine grained, bioturbated, and have low porosity, very low permeability, and high water saturation. Crossplots of resistivity, water saturation, and porosity for samples of known end member composition provide a means of correcting log values for the effects of authigenic mineral phases in noncored intervals. Variations in reservoir properties within the sandstone can be ascribed to both primary lithologic contrasts and subsequent diverging diagenetic histories. Factor analysis provides a promising approach to quantifying the relationship between siliciclastic depositional environments, diagenesis, and reservoir properties.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.