Comparison among Fracture Calibration Test Analysis Models

摘要

Recent papers show new models for matching the injection falloff response to a fracture calibration test, also known as minifrac or the diagnostic fracture injection test (DFIT), one numerical and one analytical. Both models address variable compliance, but they disagree on the value for minimum stress. The analytical model provides a way to estimate the effective permeability from the after-closure response that can be compared to an existing methodology for permeability estimation from the before closure behavior. The objective of this work is to assess where the existing interpretation models agree or disagree and the limitations on where the various approaches apply. The McClure numerical model for variable compliance results in exactly one closure instance, after which all observed behavior is matched with after closure variable fracture compliance. The Liu analytical decoupled fracture model identifies and matches multiple closure events, with variable fracture compliance and/or variable fracture surface area. The Craig model couples before and after closure behavior by treating the fracture closure as storage and matching with against a family of type curves. The original Mayerhofer method for before closure permeability estimation has clear potential advantage over techniques that require the after-closure response. If before and after closure permeability estimates are sufficiently similar, the need for acquiring after closure data is reduced to pore pressure estimation. Field examples are used to illustrate the application of the four models. The parameter values estimated from these analyses are essential to design of the main fracture treatment(s). Discrepancies in the value estimates may have profound impact on the treatment design and execution.