Marking the start of a wellbore flush volume

A system comprising:

• a fluid blending apparatus having a sensor array providing two or more sensor channels, the sensor array configured to acquire one or more blending signals, each blending signal comprising a series of time-varying blending data corresponding to a blended fluid output by the fluid blending apparatus and pumped into a wellbore such that the blended fluid transitions from a first fluid composition to a second fluid composition;
• and
• at least one processor in communication with the fluid blending apparatus, wherein the at least one processor is coupled with a non-transitory computer-readable storage medium having stored therein instructions which, when executed by the at least one processor, cause the at least one processor to, for each blending signal of the one or more blending signals:
• analyze, based on a calibration profile corresponding to one or more of the first fluid composition and the second fluid composition, a second portion of the blending signal corresponding to the second fluid composition in order to determine a transition indicator, the transition indicator corresponding to a change in the blended fluid from the first fluid composition to the second fluid composition;
• generate, based on the transition indicator, a flush signal indicating a beginning of a flush volume being output by the fluid blending apparatus and pumped into the wellbore;
• calculate a desired flush volume for the wellbore;
• and
• terminate, based on the flush signal and the desired flush volume, the output of blended fluid from the fluid blending apparatus such that a volume of blended fluid in the second fluid composition pumped into the wellbore is substantially equal to the desired flush volume.