Barnett, Woodford, and related mudrock successions in Texas Cores and outcrops

Authors: S. C. Ruppel, J. F. Gale and R. G. Loucks

Venue: 2008 American Association of Petroleum Geologists (AAPG) Annual Convention and Exhibition, San Antonio, TX, April 19-24, 2008 Field trip #6 (http://www.aapg.org)

Abstract: Outcrops are important guides to accurate interpretation of subsurface data sets. Paleozoic exposures in the Hill Country of Central Texas are direct analogs of Paleozoic successions in both the Ft. Worth and Permian Basins. As such, they have great potential to provide geoscientists with new insights into subsurface reservoirs.

Although the Hill Country region contains exposures of nearly every Paleozoic System, the most significant outcrops are of lower Paleozoic (Cambrian and Ordovician) and Carboniferous age.

The field trip will visit outcrops of the Mississippian Barnett Shale and the overlying Marble Falls Limestone and Smithwick Shale, the latter two of Pennsylvanian age. The Barnett is well known to all geoscientists and industry professionals as the host of the most productive gas reservoir in the United States, and a touchstone for successful exploitation of gas shales worldwide. The outcrops to be viewed at Stop 1 are perhaps the best exposures of this important succession. Understanding of the limited Barnett surface exposures is also greatly enhanced by subsurface cores from the Hill Country, which are currently under study by the authors. Core and log data across the region show that Barnett rocks in the Hill County area range to as much as 160 ft in thickness and are sedimentologically, geochemical and mineralogically similar to Barnett rocks in the Ft. Worth and Permian Basins in many ways.

The Marble Falls Formation (Stops 2, 3), a shallow water carbonate succession that overlies the Barnett, provides an analogue for subsurface reservoir successions in the Ft. Worth Basin, Bend Arch and Eastern Shelf area as well as for Morrow/Atokan reservoir successions in the Delaware Basin and for other Pennsylvanian carbonate successions in the in the Midland Basin and on the Central Basin Platform. Outcrops of the overlying Smithwick Shale (Stop 3) provide opportunities to examine the sedimentology, mineralogy, and geochemistry of analogous Pennsylvanian-age mudrocks in the region and compare them to Mississippian and Devonian counterparts.

Related NETL Project
This presentation is related to the NETL project DE-FC26-04NT15509, “Integrated Synthesis of the Permian Basin: Data and Models for Recovering Existing and Undiscovered Oil Resources from the Largest Oil-Bearing Basin in the United States.” The objectives of the project are twofold: (1) to produce a detailed, comprehensive analysis and history of Paleozoic depositional and reservoir systems in the Permian Basin, and (2) to create spatially integrated databases of depositional, stratigraphic, lithologic, and petrophysical properties for selected reservoir plays and stratigraphic horizons. These objectives will be undertaken and completed sequentially during the 3 years of the project. The overall objective is to provide Permian Basin operators with (a) outcrop and subsurface reservoir specific data, data syntheses, and models to be applied to geological-, engineering-, and completion-based redevelopment of existing reservoirs, and (b) a detailed regional stratigraphic framework for applying such models to new exploration targets.

Project Contacts
NETL – Virginia (Ginny) Weyland (Virginia.WEYLAND@netl.doe.gov or 918-699-2041)
University of Texas at Austin – Stephen Ruppel (stephen.ruppel@beg.utexas.edu or 512-471-1534)