2014 Rocky Mountain Section AAPG Annual Meeting

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Sussex Sandstone, Hornbuckle Trend, Powder River Basin, Wyoming: Lithofacies and Reservoir Properties in a Tight Oil Play


The Sussex Sandstone in the Hornbuckle Trend in Converse County, Wyoming, produces oil from three main facies: bioturbated sandy mudstone, bioturbated muddy sandstone, and bedded sandstone. These facies are vertically stacked in two upward-coarsening parasequences. Detailed engineering analysis indicates that all of these facies are oil-bearing reservoirs that contribute to production. The bedded facies is cross-bedded to sub-horizontally bedded, has 5 to 14 percent porosity, and .05 to 4 millidarcies permeability. The bioturbated muddy sandstone has 4 to 14 percent porosity and .02 to .5 millidarcies permeability. The bioturbated sandy mudstone has higher clay content and has 4 to 10 percent porosity and .01 to .2 millidarcies permeability. Two Sussex Sandstone cores provide examples of these facies. The Highland Flats Federal #13–11 core recovered 43 feet of bioturbated facies and 10 feet of bedded sandstone facies. This well was completed in 1984 for an IP of 175 BOPD after a DST recovered 240 feet of SO&GCM; this vertical completion has produced 188 MBO. The Brazos State #14–16 core recovered 52 feet of bioturbated facies and 2 feet of bedded facies. A DST of the Sussex in this well recovered 70 feet of drilling mud indicating low permeability, so in spite of oil and gas shows in the samples, this vertical well was plugged and abandoned in 1986. Horizontal wells recently drilled adjacent to this dry hole initially produced 600 to 900 BOPD. These two wells illustrate how modern horizontal drilling and completion techniques can recover oil that older vertical completions could not.