The instantaneous shut-in pressure (ISIP) picked from the pressure falloff following each hydraulic fracturing treatment stage has been used to evaluate stress shadowing effects and required for modeling injection treatment behavior. However, the traditional methods for estimating ISIP as the pressure extrapolated back to the pumping time from a straight line through an arbitrary series of points on a plot of Cartesian falloff pressure versus time or the log of time have no theoretical justification. Further, the ISIP picked by either of these approaches is highly dependent on the selected points. In this paper, we show a more rigorous approach to quantify the ISIP and that also enables estimation of parameters governing wellbore, perforations and near-wellbore tortuosity friction losses.
The wellbore storage (WBS) effect complicates straightforward picking of the ISIP from the pressure curve at shut-in. The existing diagnostic fracture injection test (DFIT) analysis model coupling WBS with friction dissipation that enables estimation of friction losses and the ISIP for the DFIT analysis also enables estimation of these same parameters from falloff data following the hydraulic fracturing treatment.
The pressure difference and its derivative in the log-log diagnostic plot generated from the falloff at the end of the fracture pumping treatment is an effective diagnostic plot to identify portions of the data dominated by WBS and friction losses. Coupled WBS and friction loss dominate the immediate pressure falloff after the end of pumping, and frequently the treatment data include sufficient time to quantify friction losses. The wellbore and perforation friction loss and the total friction loss are picked using the log-log diagnostic plot. Changes in the correctly quantified ISIP estimated for successive treatment stages along the horizontal well may be related to a stress shadowing effect. Field examples demonstrate how the ISIP profile along a well compares between this approach and common field practices.
The paper provides a quick approach to evaluate friction losses and the ISIP from hydraulic fracturing treatment falloff data. The approach provides much more accurate and less uncertain ISIP estimates than current field practices.