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Fracture Interpretation and Discrimination Between Drilling-Induced and Natural Fractures Through Integration of Cross-Dipole Acoustic Anisotropy and Electrical Borehole Images


Zarian, P.1, R. Reinmiller2, M. Markovic2, M. Kozimko3 (1) Baker Atlas, Houston, TX (2) Baker Atlas, Denver, CO (3) Yates Petroleum, Denver, CO


Measurements of anisotropy directions using cross dipole acoustic logging tool provide valuable information about stress orientations within the borehole. Calibration of the frac­ture data identified from electrical borehole images with cross dipole acoustic anisotropy and Stoneley wave permeability data, leads to a more precise classification of fracture types. This approach is particularly useful in structurally complex areas, such as the one present­ed in this study, where discrimination between the natural open and drilling induced tensile fractures is ambiguous. The orientation of the fast shear pathway identified from cross dipole acoustic anisotropy measurements is theoretically parallel to the orientation of the drilling induced tensile fractures from electrical borehole images, which helps to constrain the orientation of the maximum in-situ horizontal stress. Since the cross dipole acoustic tool has a deeper depth of investigation in comparison to the electrical borehole imaging tool, this difference in depth of investigation can help in discrimination of the natural fractures which propagate deeper into the formation from the drilling induced fractures which are proximal to the borehole wall. The study is conducted on a near-vertical well from Greater Green River Basin in Rocky Mountain Wyoming where the morphology of drilling induced fractures on the electrical borehole images resembled the natural open fractures, creating uncertainties in fracture classification. However, the application of the above approach helped in a successful identification of the natural open fractures which are main contribu­tors to the reservoir producibility and fluid flow creating a robust framework for making decisions for well completion purposes.