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Redtail Field, A Thermal Anomaly on the Eastern Extension of the Colorado Mineral Belt, Denver Basin, Colorado

Abstract

Redtail Field in northeast Weld County, Colorado is one of many new generation field discoveries in the past ten years in which low permeability reservoirs are intercalated with mature source rocks. Horizontal wellbores with multistage fracture stimulation are required to contact sufficient permeability feet of reservoir to economically produce hydrocarbons. This new generation Denver Basin discovery required a multi-disciplinary team to integrate vast amounts of data with a strong regional understanding of depositional, diagenetic, structural, and thermal systems. Redtail Field, like all new generation, continuous-phase, horizontally drilled fields requires a team of scientists and engineers all working with a common exploratory concept from discovery through development. The field is located on the eastern flank of the Denver Basin with nearly north-south structural strike and modest west dips of less than a half degree. However, intense normal faulting and local graben development within the Niobrara and adjacent formations commonly disrupts the regional structure and requires high-quality 3D seismic to be aggressively integrated into geosteering prognoses. In addition, faulting associated with the northeast-trending Colorado Mineral Belt provided conduits for convective heat flow and the development of isolated areas of thermal source-rock maturation. Four main pay zones have been established at Redtail Field, the Coniacian and lower Santonian Niobrara A, Niobrara B, and Niobrara C Chalks as well as the middle Turonian Codell Sandstone. Each of these 4 target intervals provides its own petrophysical challenges for sweet-spot and volumetric mapping. Interbedded chalky reservoirs and marly source rock within the Niobrara Formation put excellent source rocks adjacent to high porosity, low permeability reservoir intervals. This 350-ft gross source/pay interval is being developed with 1-2 mi long horizontal wellbores in each of the four zones. Four pilot programs determine the well density requirements for full field development. In addition, over 2000 ft of core in seven wells establish the basis for petrophysical reservoir evaluation and reservoir mapping. The discovery and subsequent development of Redtail Field can be attributed to technical contributions from the entire Redtail Team; Exploration Geologists, Reservoir Geologists, Geophysicists, Petrophysicists, Reservoir Engineers, Operations Engineers, Drilling Engineers, Landmen and Senior Management.