ABSTRACT: Basin Evolution and Reservoir Development in Silurian and Devonian Rocks in West Texas: Implications for Coeval Deposits in the Illinois Basin
RUPPEL, STEPHEN C., Bureau of Economic Geology, University of Texas at Austin, Austin, TX
Silurian and Devonian strata in the Permian basin constitute a major hydrocarbon-bearing sequence; production from more than 650 reservoirs totals about 1.8 billion bbl. Patterns and styles of reservoir development and distribution in these rocks are closely related to basin evolution. Three major stages of evolution are recognized.
The Early Silurian was characterized by shallow-water carbonate deposition on an extensive, low-gradient platform. Both deposition
and diagenesis was punctuated by episodic sea level fall. Reservoirs are primarily developed in ooid grainstones and encrinites that have undergone teaching during these and later exposure events. During the Wenlockian, the platform was downwarped resulting in considerable platform-to-basin relief. Reservoirs in these rocks are developed in platform-margin, coral/stromatoporoid buildups and in cyclic, inner-platform carbonates where porosity is enhanced by teaching associated with periodic sea level fall. Slope/basin mudstones and shales form top seals for underlying shallow-water platform deposits. A subsequent sea level rise in the Early Devonian resulted in filling of the basin by transgressive, slope/basin, spiculitic chert and progradational, highstand, skeletal carbonate.
Reservoirs are developed in cherts whose distribution is controlled by sea level cyclicity and gravity mass transport, and in grain-rich carbonates that underwent teaching during regional Middle Devonian uplift. Late Devonian shales form the top seal and source rock for the entire sequence.
Consideration of the styles of deposition and diagenesis associated with each stage of Silurian-Devonian history places constraints on models of basin evolution and reservoir development in these and equivalent rocks, such as those in the Illinois basin.
AAPG Search and Discovery Article #91013©1992 AAPG Eastern Section Meeting, Champaign, Illinois, September 20-22, 1992 (2009)