Shelf-Edge Deltaic Depositional Systems in the Upper Woodbine Succession, Double A Wells Field, Polk County, Texas
William A. Ambrose and Tucker F. Hentz
Bureau of Economic Geology, University of Texas at Austin, University Station, Box X, Austin, Texas 78713–8924
Analysis of 15 slabbed cores and ~65 wells in the Double A Wells Field in Polk County, Texas, indicates that the upper one-third section in the Upper Cretaceous (Cenomanian) Woodbine Group is composed of shelf-edge deltaic systems. The most productive well in the field, the Blackstone #7 Carter, has produced ~31.6 Bcf (billion cubic ft) of gas and ~1.7 MMbbl (million barrels) of condensate from sandy, amalgamated proximal-delta-front and channel-mouth-bar deposits that are collectively >70 ft (>21 m) thick. During periods of relative sea level fall, Woodbine incised-valley-fill systems delivered sediment southwestward from the west flank of the Sabine Uplift to the Woodbine shelf edge. Features observed in core, diagnostic of shelf-edge deltaic systems, include thick delta-front successions across the seaward, downthrown part of growth faults, and gravity-slide deposits. Distal-delta-front deposits in the Double A Wells Field, representing rapidly deposited turbidities, are commonly composed of thin (<1-ft [<0.3-m]), sharp-based, and very fine-grained sandstone beds that overlie zones of muddy, burrowed siltstone. The distal-delta-front facies grades upward into sandy proximal -delta-front and channel-mouth-bar facies. These facies are composed of fine-grained sandstone with low-angle, planar stratification and massive to ripple-laminated, upperfine- grained sandstone. Alternating beds of planar-stratified sandstone represent highenergy upper-flow-regime flows associated with channel-mouth-bar facies, whereas ripple- laminated strata record waning-flow deposits. Lenticular sandstone-body geometry in narrow distributary-channel and channel-mouth-bar deposits, inferred from grosssandstone maps, in combination with faults, controls reservoir compartments and variable well productivity.
AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012