Analysis of Wellbore Resonance Effects on Acoustic Noise Characteristics in Gas Producers

Summary Measurements of acoustic noise in production logging are aimed at locating well casing leakage, crossflow behind casing, fluid/gas inflow, etc. Interpretation of the data can be difficult because of the wellbore resonances having a significant influence on the registered signal spectrum. Using numerical modeling we investigate the spatial-frequency structure of acoustic fields in the wellbore excited by a noise source located in the near-wellbore zone. We analyze influence of geometry and physical parameters of the reservoir and wellbore on the resonances. Also, we consider an example of the acoustic noise spectrum recorded in a gas-condensate producer and conclude that the intensive acoustic signal registered along the extended depth interval is caused by wellbore resonance modes, rather than by an extended inflow zone (which according to production logging data corresponds to a narrow interval of natural fractures). On the other hand, the observed wellbore resonances enable using this natural signal amplification for more reliable inflow identification. Thus, the analysis of acoustic noise spectra by taking into account the wellbore resonances improves the precision of the determination of inflow intervals.