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Abstract

A method for measuring the linear flow velocity, radial position, direction, and the flow rate of water flowing within and behind a well borehole casing. A logging tool containing a source of essentially monoenergetic 14 MeV neutrons and at least one gamma ray detector is positioned within the well borehole opposite the zone in which water flow measurements are desired. The neutron source is turned on thereby irradiating any flowing water and other areas in the vicinity of the well borehole with high energy neutrons. After a predetermined irradiation time, the neutron source is turned off. Following a quiescent period of several milliseconds to allow thermal capture gamma radiation to decay to a negligible level, the gamma ray detector is turned on and the count rate from the N-16 induced within the flowing water is recorded as a function of time. The linear flow velocity, the Full Width Half Maximum time period, and the total count are determined directly from the resulting count rate curve. The radial position and the flow rate are determined using the predetermined relationship between the Full Width Half Maximum time period, radial position, and linear flow velocity, and the predetermined relationship between linear flow velocity, radial position, and the ratio of the flow rate to the total count for the logging tool. The direction of flow is determined by sensing the presence or absence of flowing N-16 above or below the source.

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First Claim