This paper addresses some recent developments in a production logging technique that uses Pulsed Neutron log measurements to evaluate the formation inflow into a wellbore, in which one or more of the completed intervals may be located in the annulus between the casing and tubing strings above the end of the tubing. Of particular importance in this work is the capability of determining the formation inflow profile in the well in cases where the well outflow velocity is less than that required to continuously transport and unload liquids from the well. Sub-critical velocities are commonly encountered in low productivity gas wells that produce liquids, whether they are produced directly from the formation and/or condensed well fluids, water and hydrocarbons.

This paper presents a sub-critical velocity analysis that has been implemented in a Pulsed Neutron production logging technique in order to have the capability to reliably evaluate the formation inflow into wells in which the velocities are so low that no other production logging methodology is possible. Coupled with the numerical modeling of the Pulsed Neutron production log evaluation, test pit measurements of the annular flow water velocities with the Pulsed Neutron logging technique have been reliably and accurately measured to as low as 3 ft/min (0.05 ft/s).

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