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Predicting Natural Fractures in Unconventional Reservoirs: Examples of Data Validation Techniques From the Bakken System, Mountrail County, North Dakota

Buckner, Steve J.; Nelson, Ron; Bayer, Sebastian; Lozano, Felipe A.; Chen, Jason; Rasdi, Faisal; Brown, Peggy

The Bakken System of the Williston Basin is defined as an unconventional reservoir due to the following characteristics; low permeability, "continuous type" reservoir, and the lack of conventional fluid contacts. Studies to understand and optimize completion strategy in the Bakken System of Mountrail County, North Dakota led to the acquisition of a diverse dataset. This data along with the recognition that natural fractures probably locally represent the essential permeability for the Bakken System (Class II fracture reservoir of Nelson, 2001) provided the impetus for a fracture characterization study to understand how natural fractures might relate to productivity and stimulation success.

This study resulted in a rich database, of regional extent, constructed using core-based fracture and facies descriptions from 56 wells (including 3 horizontal wells). Relating natural fracture abundance to productivity is challenging due its reservoir and wellbore complexity. The purpose of this case study is to describe the fracture database including the strengths and limitations of the various data types, to discuss some of the techniques found useful for validating and integrating different data types, and to describe methodologies used for predicting the abundance of natural fractures in the Bakken System of the Williston Basin.

This paper demonstrates a) pre-stimulation data can be used as indicator of natural fractures system, b) observed correlations between fracture counts from vertical cores and rigidity can be used to define a relative mechanical stratigraphy and natural fracture abundance, c) the relationship to structural curvature can be used to define the spatial variability of natural fracture abundance, d) observed correlations between fracture counts in horizontal image logs and curvatures attributes derived from 3-D PP seismic data can be used to build functions to characterize fracture corridors in terms of frequency, widths and fracture abundance, e) natural fracture observations can be used to construct a library of predictive models for regional, fold-related, fault-related, and diagenetic fractures and f) the discrete fracture networks models were later validated using both results from the literature and also by acquiring new data (horizontal image log, microseismic data and pressure communication).


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013