Silo Field, located in the northern Denver Basin, is an important field for Niobrara oil production. The production is heavily controlled by the presence of open, vertical, natural fractures but the genesis of these features is not understood. A 3-D seismic survey, covering approximately 30 square miles in the heart of Silo Field was interpreted to determine the nature of the fractures. It also aided in the examination of the Permian salt edge and the Precambrian basement in the field. FMI logs and core descriptions provided additional information for the study. Based on the interpretations, the faults and fractures of the Niobrara have various causes including: underlying basement structure and dewatering during burial compaction. The Permian salt edge is oriented NW-SE across the survey area and an isochron from the Permian salt to the Wolfcamp (base salt) horizons illustrates the highly irregular nature of the salt edge. The irregularity of the salt edge suggests that salt dissolution created the edge rather than salt deposition. Where the salt is absent in Silo, a thickened Dakota-Sundance interval compensates for the lack of salt. This compensation creates a structural monocline in the strata overlying the salt edge due to differential compaction. Differential compaction is not the only cause for the monocline. Examining the basement horizon shows that there are possible basement faults that also contribute to the location of the structural monocline within Silo Field. It is also likely that basement faults control the location of the salt edge. Analyses of FMI logs within and outside of the main field area demonstrate that the orientation of natural fractures changes rapidly over short distances. In the southern part of the field, the dominant fracture orientation is NW-SE, similar to the underlying basement structure. Less than five miles south of the field, the fracture direction changes to a more N-S orientation. This has implications for future development of Silo Field and careful consideration is needed when attempting to develop outside the main field area.

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