Integrated Core, Well Log, and Seismic Interpretation of Lower Glen Rose (Albian) Buildups in Maverick Basin, SW Texas

Stratigraphic analysis of well logs and seismic stratal-slices indicates that the Lower Glen Rose Formation, Maverick Basin, comprises four units. From bottom to top, the units record the HST of sequence 6 and all of sequence 7. The reef interval comprises sequence 7 and consists of three reef levels throughout units 2-4. Buildups in unit 2 change from transgressive isolated buildups into a flat biostrome. Unit 3 buildups record a landward shift relative to the biostrome of unit 2, as shown on well logs. Unit 4 buildups record seaward shift of bioherms relative to unit 3.

Development of an individual reef level occurred mostly in decreasing accommodation trends of high-frequency sequences, as described for two cored buildups in unit 4. Shoaling-reefal buildups correlate with a distinctive clean, blocky gamma-ray response and strong negative seismic amplitude anomalies. Off-reef deposits correlate with a higher, variable gamma-ray response and positive seismic amplitudes. The shoaling-reefal facies may be gas reservoirs; gas potential concentrate in units 2 and 4.

Geomorphometric analysis based on seismic stratal slices and > 30 buildups of unit 4 determined that the domal features elongated NNW-SSE, with steeper SW flanks. Asymmetry of the shoaling-reefal buildups may be the result of NW-directed far-field paleo-currents and NNE-directed, wind-driven paleo-waves. Independently of the size scale, the elongation axis of buildups is 1.5-2.5 times larger than its perpendicular direction. Results imply best reservoir facies in the SW side of the Lower Glen Rose patch reefs.