--> Abstract: Sequence Stratigraphy of the Eagle Ford (Boquillas) Formation in the Outcrops of West Texas & Subsurface of South Texas, by Art Donovan, W. Li, A. Pramudito, and Scott Staerker; #90124 (2011)

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AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Sequence Stratigraphy of the Eagle Ford (Boquillas) Formation in the Outcrops of West Texas & Subsurface of South Texas

Art Donovan1; W. Li1; A. Pramudito1; Scott Staerker2

(1) BP, Houston, TX.

(2) BP Exploration Production Technology

The Upper Cretaceous (Cenomanian- to Coniacian-aged) Eagle Ford Formation contains unconventional mudstone reservoirs that are presently being exploited in the subsurface of south Texas. In order to better understand the facies, age, distribution, and thickness variations of these reservoirs, a sequence stratigraphic analysis of the Eagle Ford (Boquillas) succession was conducted in the outcrop belt in West Texas, as well as the subsurface of South Texas.

In the road cuts and canyons along US Highway 90, northwest of Del Rio, excellent exposures of the Eagle Ford (Boquillas), underlying Buda, and overlying Austin are present. These outcrops, which can extend thousands of feet laterally and hundreds of feet vertically, provide a unique opportunity to examine these strata in detail. Recent work indicates that the Eagle Ford succession in outcrop can be divided into 3 depositional sequences. In general, each sequence consists of a lower portion dominated by organic-rich carbonate mudstones and an upper portion consisting of carbonate mudstones with limestone inter-beds, which are interpreted respectively as transgressive and highstand deposits. Furthermore, the key sequence stratigraphic surfaces (sequence boundaries & maximum flooding surfaces) defined in outcrop, serve as robust correlation horizons which can be used to map and define the same sequences and systems tracts in the subsurface of South Texas. This sequence stratigraphic analysis indicates that the Eagle Ford is not one homogeneous reservoir unit, but a more complex vertically heterogeneous succession of distinct chronostratigraphic units each with distinct reservoir characteristics and properties.