The Effects of the Petrology and Diagenesis of Mixed Provenance Sand-stones on Permeability Heterogeneity and Reservoir Characterization

DUNN, THOMAS L., University of Wyoming, Laramie, WY, ROBERTO J. MERINO, Amoco Argentina Oil Company, Buenos Aires, Argentina, and RONALD C. SURDAM, University of Wyoming, Laramie, WY

The Comodoro Rivadavia Formation of the north flank of the San Jorge basin is a fluvial/alluvial fan sequence deposited during the late sag stage of rift basin development. Basin fill was derived from the eroding volcanic arc to the west and northwest, contemporaneous volcanism, and the basement found to the north.

Three petrofacies are recognized: a dominant petrofacies derived from plutonic, volcanic, and metasedimentary rocks [Q(21)F(21)L(5 2)]; a monolithologic volcanogenic sandstone composed entirely of volcanic detritus [Q(6)F(21)L(69)], and a petrofacies recognized as a diagenetically (meteoric) altered derivative of a mixed provenance petrofacies [Q(48)F(25)L(43)]. Lateral and vertical variation of sandstone composition provides independent constraints on correlation of sandstones across a portion of the north flank.

Factors which govern the diagenesis of the sandstones include burial history, compositional variations, meteoric influx, and presence and compositional variation of infiltrated material. Formation of late smectite as a result of uplift of the basin has increased heterogeneity of permeability. The meteorically altered sandstones have permeabilities that vary three orders of magnitude more than those sandstones that were not strongly leached. Infiltration of fines has reduced permeability, although the composition and extent of infiltration varies greatly. These postdepositional processes have played an important role in determining reservoir heterogeneity.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)