Acoustic signatures of crossflow behind casing in commingled reservoirs: A case study from Teapot Dome

Cracks and channels in cement often create unwanted conduits behind casing that lead to crossflow between different producing zones. Crossflow results in lost production or aquifer contamination because fluid flows from a higher-pressure to a lower-pressure zone instead of traveling up the well. We present measurements of acoustic signatures of crossflow behind the pipe in time and frequency domains. Despite being called "noise," they are shown to be propagating tube waves with impulsive signatures. When multiple crossflow locations are present along the well, these signatures are unique for each location and are highly repeatable. We observe time-lapse change in such signatures during air injection and release and suggest that these changes can be used for real-time acoustic characterization of depletion in stacked commingled reservoirs. We anticipate that such signals are typical for commingled production of multilayered reservoirs. Acoustic signatures can be used to characterize crossflow and depletion. In addition, crossflow signals represent a strong noise affecting downhole seismic surveillance with active sources.