Defining Depositional Facies Within a Chronostratigraphic Framework: Paluxy Formation (Lower Cretaceous), Talco Field, Northeast Texas
WINTERS, WARREN J., Exxon Company USA, Houston, TX, A. JAMEOSSANAIE and C. R. JONES, Exxon Production Research Company, Houston, TX, and E. M. HOOVER, Exxon Company USA, Houston, TX
Talco is a heavy oil field at the northern end of the East Texas basin that has produced over 275 million bbl in its 55-year life. Production is from predominantly fluvial sandstones of the Paluxy Formation (Albian) at 3750 to 3975 ft subsea. The field is a high-side fault trap along the north-dipping Talco fault, which juxtaposes Paluxy reservoirs against the shales and limestones of the Washita Group. The productive interval is unfaulted within the field limits.
A detailed stratigraphic study was undertaken in a 185-well area near the west end of the field (Penn Fee study area). A grid of field-wide cross sections was also produced to relate the detailed geology to a broader stratigraphic framework. Well logs, conventional core, and micropaleontology indicate the Paluxy Formation is a retrogradational stratal succession. Laterally continuous braided-stream deposits grade upward into flood-plain sands and shales, and finally into brackish to shallow marine mudstones and thin, laterally continuous sandstones. Local truncation of shale marker beds in these marine, brackish, and flood-plain facies defines three erosional surfaces within the upper Paluxy. Each of these erosional surfaces is overlain by 12 to 60 ft of blocky to upward-fining, fluvi l to estuarine sandstone. These form dip-oriented sand bodies and are believed to represent incised valley-fill deposits. Each valley-fill package is overlain by a shale member that is correlatable field wide. Throughout some of the Penn Fee area, two or three valley-fill packages are amalgamated to form a reservoir complex up to 89 ft, overlain field wide by a highly bioturbated shallow marine mudstone, a transgressive marine sand and shale, and the limestones and shales of the Fredricksburg Group.
The Paluxy Formation at Talco field records an overall deepening event punctuated by three distinct base level falls. These sharp base level shifts may be reflecting either local conditions of subsidence or sediment supply, or shifts in eustatic sea level. Regardless of their origin, recognition of these erosional surfaces is essential to building an accurate field-wide chronostratigraphic framework within which depositional facies can be defined and mapped and reservoir continuity accurately modeled. Additional biostratigraphy and regional stratigraphic studies are planned to place the Paluxy Formation at Talco within a sequence stratigraphic framework.
AAPG Search and Discovery Article #91006 © 1991 GCAGS and GC-SEPM Meeting, Houston, Texas, October 16-18, 1991 (2009)