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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Petrology
Vol. 61 (1991)No. 6. (November), Pages 909-920

Previous HitPorosityNext Hit Trends of the Lower Cretaceous J Sandstone, Denver Basin, Colorado

James W. Schmoker, Debra K. Higley

ABSTRACT

This study examines relationships between Previous HitporosityNext Hit and time-temperature history, and the influence of rock properties upon Previous HitporosityNext Hit, for the Lower Cretaceous J sandstone in the Colorado portion of the Denver basin.

The J sandstone is classified as a quartzarenite to litharenite and was deposited in nearshore-marine, deltaic, and fluvial-estuarine (valley-fill) settings. Principal elements of its paragenetic sequence include quartz cementation and pressure solution, carbonate cementation and dissolution, dissolution of feldspar and rock fragments, and formation of authigenic clays.

Previous HitPorosityNext Hit Previous HitversusNext Hit vitrinite reflectance (R0) regression lines of the form ^PHgr = A(R0)B (where B is a negative number) depicting the 10th, 25th, 50th, 75th, and 90th Previous HitporosityNext Hit percentiles of the J sandstone were derived from 963 core-plug measurements representing 31 wells. The data span a thermal maturity range of R0 = 0.41%-1.14%. Previous HitPorosityNext Hit distributions at different locations within the basin can be estimated as a function of thermal maturity on the basis of these regression lines. Previous HitPorosityNext Hit trends of the J sandstone, if considered as a function of R0, are similar to those of broad, composite data sets representing sandstones in general.

The petrographic factors that most affect J sandstone Previous HitporosityNext Hit variability at a given level of thermal maturity are carbonate cementation and clay content. Carbonate cement, where present, reduces Previous HitporosityNext Hit. If previously more widespread, carbonate cement could also introduce Previous HitporosityNext Hit heterogeneity by temporarily preserving the pore network relative to uncemented intervals. Abundant detrital and authigenic clay reduces Previous HitporosityNext Hit by occupying pores. Low clay content indirectly reduces Previous HitporosityTop because the inhibiting effects of clay upon quartz cementation and pressure solution are largely absent.


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