2014 Rocky Mountain Section AAPG Annual Meeting

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Sussex Sandstone Tight Oil Play, Powder River Basin, Wyoming, Extension of the Hornbuckle-Spearhead Trend with Horizontal Drilling


Oil production was first established from the Campanian Sussex Sandstone in the Powder River Basin with the discovery of House Creek Field in 1968. Oil production from a second Sussex Sandstone trend was discovered when production was established at Spearhead Ranch (1983) and Hornbuckle (1984). The first Sussex horizontal well in the Hornbuckle-Spearhead trend was drilled in 2006 by Southwestern Production Corp. The Blaylock-Federal #13–35A had excellent shows, but high formation pressures necessitated completion of the well through cemented drill pipe, resulting in a peak rate of 79 BOPD. Overpressure up to 0.65 psi/foot was underestimated due to low reservoir permeability. This geological success set the stage for additional horizontal drilling, which has now increased Sussex production in this trend from less than 500 BOPD to more than 6500 BOPD and basin wide Sussex production to more than 8000 BOPD. The Sussex Sandstone at Hornbuckle consists of interbedded very fine to medium-grained glauconitic and calcareous sandstone, chert pebble and siderite-clast conglomerate, and silty shale. These heterolithic strata are burrow-mottled at the base and coarsen upwards. Burrow structures show a change from Cruziana to Glosssifungites ichnofauna, corresponding to the overall bathymetric shallowing and coarsening of detritus. Porosity ranges from 4 to 14 percent and is developed within the entire sandstone interval, with the best porosity developed in the higher-energy facies. Engineering analysis of production data identifies heterogeneities not observed with widely-spaced geological data, establishes the importance of the bioturbated facies to net pay, and facilitates mapping of reservoir compartments. Integration of geological models with production data analysis provides a consistent reservoir description that can be used to help maximize production from horizontal and vertical well development.