Faults and fractures in the Niobrara Formation of Wattenberg field, Colorado

Abstract

Faults are an important element of reservoir characterization because they have the potential to compartmentalize a reservoir and create associated fractures that can profoundly influence fluid flow in the reservoir. This investigation describes details of the fault regime in a portion of the Wattenberg Field, Colorado. For the purposes of this study, seismic-scale faults are interpreted as horizons with displacements. Seismic-scale fractures are interpreted as linear amplitude discontinuities. Borehole image log scale faults show displacement. Borehole image log scale fractures do not show displacement. Both borehole image log scale faults and fractures are interpreted as seismic-scale fractures. Faults were discovered by interpreting inflection points in cumulative dip plots and azimuth walkout plots derived from a borehole image log in a vertical well. On the image log fractures are consistently found in both the Niobrara chalk and marl benches. The individual benches are not resolvable at the scale of the seismic data, but evidence that faults are present in both the chalks and marls lends credence to the potential that seismic data may be able to predict fracture zones either directly or indirectly. The hypothesis is tested on a 50 square mile 3D seismic survey. Generally, faults present in the Niobrara Formation in the survey are planar, normal faults that range up to two miles in length. Over 150 faults were picked. Rose diagrams illustrate a predominant strike direction of N 20 E. A predictive fracture volume was generated utilizing CGG’s proprietary software: InsightEarthTM. The algorithm generates this volume statistically based on fault geometry. Each seismic-scale fault indicates a high potential for fracture swarms in the nearby vicinity. Fracture prediction can assist future exploration and development in the Niobrara resource play.