2014 Rocky Mountain Section AAPG Annual Meeting

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Wide-Azimuthal 3D Seismic Data Integrated with Geologic Information from Open-Hole Logs Unlocks the Secrets of a Naturally Fractured Trap in the Western Uinta Basin, Utah


Test results from an exploratory well drilled into the upper Wasatch Formation north of Brundage Canyon Field in late 2012 indicated that the bulk of the production came from naturally fractured zones. With an initial production rate of over 500 BOPD from thin-bedded, low porosity sandstones in the exploratory well, it was important for the asset team to understand the role of natural fracture enhancement before field development began. To assist with development planning, a wide- azimuthal 3D seismic survey was shot across the prospect and surrounding area. Although geo-mechanical properties such as Young's Modulus and Poisson's Ratio may be extracted from wide-azimuthal data, the primary objectives of the 3D survey were to gain a better understanding of the regional structural fabric adjacent to the Duchesne Fault zone and estimate natural fracture intensity and orientation. Data from borehole image logs run in the exploratory well and several early wells showed a high frequency of open fractures with a dominant NW to SE direction in the Castle Peak Member of the lower Green River Formation. However, zones with a high frequency of open fractures in the underlying upper Wasatch Formation exhibited multiple directions. Production log runs indicated that these intervals contributed significant production to the wells. The combined data set substantiated results from the 3D survey which showed high anisotropy associated with the Castle Peak and low anisotropy for the upper Wasatch intervals. Integration of wide-azimuthal 3D seismic data with borehole image and production log results was very important in understanding reservoir characteristics and mapping areal limits of naturally fractured “sweet spots”. Thirteen wells have been drilled to date with an average per well EUR of approximately 100 MBOE. When full development is completed, the anticipated reserves will approach 2.0 MBOE.