Abstract

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, upper-fine-grained sandstone. Alternating beds of planar-stratified sandstone represent high-energy 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 gross-sandstone maps, in combination with faults, controls reservoir compartments and variable well productivity.