6 system 200 includes a measuring unit 16 for measuring time of arrival of the injected fluid at temperature sensor 8 a communication link 7 connects temperature sensor 8 with unit 16 and optionally other units not illustrated communication link 7 may be fiber optic hard wire or wireless although communication link 7 is illustrated as traversing through tubular 2 and tubular section 4 link 7 may traverse in the annulus between tubular 2 and wellbore or production casing 3 fig3 illustrates schematically another system embodiment 300 within the invention and includes a tubular 2 inserted in a cased or uncased wellbore 3 in a formation 5 tubular 2 comprising a section of tubing 4 having at least one fluid injection port 6 and at least one sensor 8 placed at a known location on tubular section 4 system 300 includes a first pump 10 a for injecting a first fluid through tubular 2 tubular section 4 and the at least one fluid injection port 6 the first fluid having a first fluid property value and a second pump 10 b for injecting a second fluid through an annulus between tubular 2 and the cased or uncased wellbore 3 the second fluid having a second fluid property value that is different from the first fluid property value system 300 includes a measuring unit 18 for measuring a differential between the first and second fluid property values the first and second properties may be temperature pressure flow rate conductance or.