a method of measuring fluid in - flow in a region of interest in a wellbore comprises deploying a fiber optic cable concurrently with placement of a downhole tubular , transmitting a light signal along the cable and receiving a reflected signal from the region of interest , and interpreting the received signal to obtain information about fluid flowing in the region of interest . the wellbore may include a horizontal portion . the received signal may also be interpreted by assessing amplitude and frequency spectra across array of channels , conditioning the received signal by removing at least a portion of the signal that is not related to flow , assessing flow regimes across depths and times , calculating axial flow / s within the wellbore using relationships for axial flow , and calculating flow into or out of the wellbore at one or more points using relationships for flow through an orifice .