Abstract
For economic production, the heterogeneous low-permeability Achimov formation of the Urengoiskoe field requires stimulation with high-volume hydraulic fracturing. Shales acting as stress barriers are present within the reservoir, dictating the necessity of fracture geometry monitoring and design accounting for local changes in mechanical properties. A new slim dipole sonic tool enables a reliable identification of fracture geometry in the near-wellbore region. The tool dimensions allow it to be run in environments unsuitable for conventional-sized sonic tools such as completions with a small inner diameter.
Analysis of sonic data in three wells reliably identified unintended fracture growth from the lower target Ach6 reservoir through the shale barrier into the upper Ach5 reservoir. Calibration of the fracturing model using the measured fracture height reveals that the main uncertainty in fracture geometry prediction originates from the input formation mechanical properties and stress profile. Therefore, fracture design optimization should include updates to the geomechanical model with account for the presence of structural VTI-anisotropy as well as justified dynamic-to-static conversions, refined pore pressure profiles, etc.
This paper demonstrates the use of dipole sonic pre- and post-frac logs to determine the real fracture height as well as the corresponding impact on the calibrated fracture model. A way forward is proposed to improve geomechanical models by including sonic-based anisotropy parameters to improve fracture geometry predictability in target zones.
