Volume to first response (VFR) and frac hit trackers give you a direct way to quantify hydraulic fracture crossings between wells. They are useful for diagnosing well interference, calibrating frac hit behavior, and tying simulation results to field observations. This document explains how each tracker works and how to interpret the values written to the tracking file.
To use either tracker, specify an ‘injection well’ and an ‘observation well.’ The simulator then writes one column per tracker to the tracking file, indexed by stage on the injection well.
The VFR tracker reports the volume of fluid injected into a given stage of the injection well prior to the first fracture crossing at the observation well. Before any crossing occurs — and whenever the injection well is inactive — the VFR column displays “nan.” Once a fracture crosses the observation well, the column populates with a numeric value. When pumping stops, the value resets to “nan.” Note that reopening of preexisting hydraulic fractures is not counted as a fracture arrival.
The frac hit tracker reports the count of fracture crossings at the observation well during each stage of injection. The column displays “-1” while the injection well is inactive, “0” during active pumping until the first crossing, then increments by one for each subsequent crossing in that stage. At the end of the stage the column resets to “-1”. Note that reopening of preexisting hydraulic fractures is not counted as a frac hit.