Integrating Core, Well Logs and Seismic Interpretation to Improve Understanding of Albian Patch Reefs, Maverick Basin, SW Texas

E.S. Aconcha¹, C. Kerans¹, and H. Zeng^2
1Jackson School of Geosciences, University of Texas at Austin, Austin, TX
²Bureau of Economic Geology, Austin, TX

Using the stratal slicing technique, a seismic sedimentologic analysis was performed on the mid-Albian carbonates of the Glen Rose Formation, Maverick Basin, SW Texas. The 3D seismic subset covers an area of 186 km² and is integrated with 68 wells, 2 cored intervals and 40 thin sections. A retrogradational stacking pattern is documented from the sequential development of shallow platform buildups with an early phase in the south (basinward) followed by a younger phase in the north (landward). This suggests the mound growth occurred during the TST of the lower Glen Rose composite sequence. The external shape of the buildups on each stratal slice was reconstructed through the geometrical parameters computed from the best-fit ellipses. Buildup area decreases over time, with buildup cores migrating westward, and average external shape becoming NNW-SSE elongated. The repose angles of the patch reefs show very steep west margins, with values that in the SW direction frequently exceeds 50 degrees. East-facing flanks display more gradual 12-20 degree dips. The implications of these morphological patterns may be related to prevailing currents and winds during buildups growth. Patch reefs usually display a clean box-shape gamma ray pattern (5-20 GAPI and low variance) and are associated with the highest negative seismic amplitudes. Positive seismic amplitudes pair with a jagged (mud-rich) GR (20-60 GAPI and high variance). Negative seismic amplitudes close to the zero crossing may show either a clean box or muddy jagged GR response. The stratal slices reveal that positive amplitudes define positive relief features (mud mounds) preceding the buildup facies proper. Before this result, buildups were thought to develop on top of the relatively flat shallow platform.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas