TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractToday, mature fields are a major interest for many oil companies since their un-recovered potentials are expected to help satisfy the worlds growing oil demand. However, while operating in such fields companies face new challenges.As such, many mature fields show under-hydrostatic reservoir pressure due to depletion, which might lead to no returns to surface during workover operations. No returns to surface make it impossible to recognize any losses as an indicator for potential formation damages or gains as an indicator for a potential kick.The crucial question is therefore how to recognize losses or gains in real time without returns to surface during workover operations?Knowing the depth of the fluid level in the well at any point in time would allow recognizing losses and gains, simply by monitoring all the changes of the fluid level in the well. This paper presents a newly developed measurement approach using a specially designed echometer that allows monitoring the fluid level in the well without returns to surface during workover operations automatically in real time, which is a fundamentally new application for an echometer.All the technical requirements that were identified to be critical for this measurement approach are highlighted in the paper. Further the paper lines out all the associated technical challenges that were faced while implementing this measurement approach. Finally, reliability and functionality of the measurement approach were proven in a series of field tests under various operational conditions.

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