Petrography and Reservoir Quality of Onshore Miocene Sandstones in the Burgos Basin, Mexico
S. P. Dutton1, T. F. Hentz1, A. Cuevas2, and J. J. Hernández
1 Bureau of Economic Geology, The University of Texas at Austin, Texas
2 Pemex Exploración y Producción, Poza Rica, México
3 Pemex Exploración y Producción, Reynosa, México
Petrographic analysis of onshore Miocene sandstones from the Burgos Basin was used to evaluate diagenetic controls on reservoir quality. The sandstones were deposited in deltaic and shelf environments. Most of the samples are from fourth-order highstand systems tracts within third-order transgressive systems tracts. A few samples are from third-order highstand systems tracts. Sandstones from nine conventional cores between depths of 5,084 and 9,833 ft (1,550 and 2,998 m) have an average composition of 58 percent quartz, 19 percent feldspar, and 24 percent rock fragments and are very fine grained, arkosic litharenites and lithic arkoses. Abundant carbonate and volcanic rock fragments in the sandstones were derived from Cretaceous carbonates and Tertiary volcanics that are exposed in the sediment source areas of the ancestral Rio Grande in Mexico and West Texas. Detrital intergranular clay and silt (matrix) content ranges from 0 to 47 percent. Calcite is the most abundant cement, averaging a volume of 10 percent. Thin-section porosity ranges from 0 to 28 percent and averages 15 percent in the clean sandstones; most pores (73 percent) are intergranular.
The main controls on porosity are volume of matrix and volume of calcite cement. Well-developed, upward-coarsening sandstones that were deposited in small bayhead deltas retain good reservoir quality where calcite cementation was not extensive. By comparison, sandstones and siltstones deposited in distal deltaic or shelf environments were extensively burrowed, contained abundant matrix, and had low porosity and low permeability from the time of their deposition. Reservoir quality is thus controlled mainly by the original depositional environment and calcite cementation.
AAPG Search and Discovery Article #90032©2004 GCAGS 54th Annual Convention, San Antonio, Texas, October 10-12, 2004