A formation test tool takes pressures or extracts a sample of formation fluid at a specific depth in a well. The area of the sample probe is small compared to the area of borehole opened up during a flow test. During a WFT pretest formation fluid is flowed into a tiny (20-50cc max) chamber over a period of minutes. During a flow test the well is flowed for hours. The data sets acquired by a formation test tool and a wireline formation test tool overlap in some respects (eg stabilized formation pressure) but in other areas they are different.
A flow test is the nearest analogue to a well on production so will always give the most accurate indications of commerciability of a well....and for many investors interest only passes luke warm levels when they see footage of a dirty great flare.
