Recent analytical models for abnormal and normal leakoff mechanisms of the pressure falloff behavior in fracture calibration tests (DFITs) provide means to match virtually all of the behavior. The match provides both the parameters related to normal leakoff behavior including closure pressure and the leakoff coefficient as well as abnormal leakoff parameters including tip extension distance and minimum fracture propagation pressure, closure pressures, leakoff coefficients, and leakoff areas for the coupled primary and secondary fracture system. The purpose of this paper is to provide a methodology for identifying these behaviors and quantifying all of the before closure parameters of interest to design of the main fracture treatment.
We use the behaviors seen on the log-log Bourdet and the G-function derivatives to identify a sequence of flow regimes and to estimate starting values for the parameters associated with each leakoff behavior. Simulation result with these starting estimated values are able to catch all identified leakoff features. Then we adjust the parameter starting values to achieve a global smooth match for the falloff data.
Equations developed for quick estimation of the starting values facilitate the model match with data. Several field cases with pressure dependent leakoff (PDL), tip-extension, multiple-closure phenomenon and transverse storage are taken as examples to illustrate the comprehensive modeling capability. The additional parameters quantified by this methodology have their reasonable physics and greatly enhance understanding of the role of tip extension and the induced secondary fracture system in the hydraulic fracture stimulation.