Unconventional reservoirs require hydraulically fractured horizontal wells in order to produce reservoir fluids economically. Induced hydraulic fractures interacting with pre-existing natural fractures results in complex fracture networks (CFNs). Even though hydraulic fracture propagation has been investigated extensively, there is indeed a lack of good understanding of characterization approaches for pre-existing natural fractures. This work presents a practical CFN generation approach by incorporating stochastic algorithms, core, and microseismic data.

Based on analysis of geological structures and core observation, natural fracture density, length, and strike distributions can be obtained. Fracture length follows a power law distribution constrained by minimum, maximum and cutoff lengths as well as a distribution exponent. Fracture strike follows a Fisher distribution. Then, microseismic event locations are used to constrain fracture centers of stochastically generated natural fractures. Moreover, a fast proxy model is developed for hydraulic fracture propagation, which honors both the total mass volume of the pumped proppants, and the pre-defined reference lengths. Finally, a field case study is used to demonstrate how to apply the proposed fracture generation and simulation workflow to model hydraulically fractured horizontal wells.

The proposed workflow implemented stochastic algorithms with the capabilities to incorporate as much information as possible such as core analysis and microseismic information, and to evaluate uncertainties due to pre-existing natural fractures. With the assumption that microseismic event locations are reactivation of pre-existing natural fractures, the perturbed event locations constrained the locations of the natural fracture centers, resulting in a better description of microseismic-derived stimulated reservoir volume. The simplified hydraulic fracture propagation scheme was able to efficiently estimate the resulting complex fracture networks, and to accurately honor the material balance during fracturing treatment. Sensitivity analysis showed that fracture permeability, matrix porosity, and matrix permeability of the CFNs affect well production performance, significantly.

This paper discusses how to utilize available data resources to generate representative CFNs for hydraulically fractured horizontal wells. The process of data preparation for each step of the workflow is discussed in details to facilitate engineers to solve practical problems with the developed methodology.

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