The ability to effectively enhance production through hydraulic fracturing is dependent on an accurate description of the reservoir production mechanism(s). Fracture designs may differ greatly depending on the production mechanism(s). The complex nature of hydraulically fractured reservoirs in which the predominant production mechanism is a set of interconnected, naturally occurring fractures is investigated in this paper. The paper integrates general reservoir simulation results with actual field data from a naturally fractured reservoir in the Piceance Basin, Colorado.

The study investigates a variety of natural fracture/matrix properties and compares the productivity of these naturally fractured reservoirs to homogeneous reservoirs with the same average flow capacity. The paper also investigates the influence of natural fracture anisotropy on hydraulic fracture design. The effect of damage to the natural fracture system is illustrated and compared to analogous homogeneous reservoirs. The economic considerations associated with many of the reservoir production mechanisms are presented.

The results of the reservoir simulations indicate that optimum fracture lengths for isotropic, naturally fractured reservoirs are identical to those estimated for homogeneous reservoirs having the same average flow capacity. Therefore, accepted fracture design considerations to determine optimal fracture length and conductivity can be used in isotropic, naturally fractured reservoirs based on the average flow capacity of the reservoir. However, fracture design considerations are more complex when the effects of natural fracture damage and anisotropy are encountered.

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