AN INTEGRATED APPROACH TO EVALUATION OF HORIZONTAL WELL PROSPECTS IN THE NIOBRARA SHALE

Integrated use of surface and subsurface geologic data, structural def ormation analysis from second-derivative maps, and dimensionless type curves in identifying potential horizontal well locations in the fract ured Niobrara Shale of northwest Colorado is described. The analysis i ncluded construction of detailed structure maps from surface geology w ith tie-ins to seismic surveys and well control and of second-derivati ve maps that were overlaid on production data to determine the minimum radius of curvature required for commercial production. Reservoir pro perties were calculated for known fields from type-curve matching with type curves for dual-porosity, anisotropic reservoirs with stress-sen sitive permeability. The curves were constructed for vertical and hori zontal wells by use of reservoir-simulation models. Spacing and econom ics of drilling horizontal Niobrara wells in northwest Colorado were e valuated. The analysis suggests that recoverable oil from the fracture d Niobrara in northwest Colorado averages 1,392 bbl oil/acre on the ba sis of a productive fracture area identified by second derivatives of the structural surface with values > 1 x 10 (-4.5) ft (-1). It is also indicated that horizontal well spacing in the fractured Niobrara shou ld be > 640 acres. In some instances, it may be more economical to dev elop the fractured Niobrara with vertical rather than horizontal wells .