From Leak Path Detection to Quantitative Flow Profiling: The Exciting Journey of the Noise

Downhole well surveillance is considered, during an asset exploitation, a mainstay for the proper characterization of well completions and reservoir behavior. For these activities, specific tools have been developed to address wellbore integrity issues (e.g., sonic, ultrasonic, electromagnetic logs) and to depict downhole dynamics in injectors/producers (i.e., production logging). However, these standard techniques may have some limitations. For instance, cement logs provide an indirect static picture of the cement placement scenario and are not able to highlight fluid movement behind tubulars if present. On the other hand, production logging can only capture fluid flow inside the completion. Therefore, it is not possible to know the flow path from the reservoir towards the well, together with the active reservoir units. Advanced Noise Logging (ANL, operating in a wide frequency range) can be an elegant solution to overcome these limitations. This paper first shows how ANL is the key to addressing tricky wellbore and completion integrity issues and then introduces a novel methodology for the quantitative use of ANL by means of an in-house spectral analysis of the recorded data. The versatility of ANL makes it suitable for multiple uses, and this is demonstrated here by several selected case histories involving different commercial tools. In detail, the measured signal (associated with particular fluid flow paths) is modeled to extract noise power amplitudes in specific frequency ranges and qualify fluid movements through the reservoir, cement channels/microannuli, pipes, and other completion elements (such as leaking valves and packers). For what concerns the presented wellbore integrity applications, the enhanced spectral analysis has provided a detailed noise classification and allowed a robust identification of the issue preparatory to possible remediation actions. Further, from a quantitative standpoint, modeling of ANL data in injection/production wells has been implemented to assess the relative flow rate in the borehole, the relative flow rate in the reservoir, and actual net pay. The latter are unique outcomes from ANL that are fundamental in challenging environments where standard production logging interpretations are not consistent or not exhaustive: the presence of asphaltenes, waxes and/or solids in the borehole, highly heterogeneous reservoirs, stimulated scenarios, and complex completions. It is worth mentioning that the reliability of such ANL-based dynamic characterization has been validated in standard scenarios with conventional production logging results (for more than 20 surveys). The novelty of the approach relies on the key role played by the enhanced modeling of ANL data and the demonstrated versatility of the measurement, with applications spanning from unusual poor cement placement issues to completion microleaks. Moreover, the quantitative use of noise power amplitudes in selected frequency ranges is relatively new and puts ANL in a prime location for the dynamic characterization of very complex scenarios when the fluid flow path behavior near the wellbore is nontrivial. Finally, the outcomes of the extensive ANL analysis represent a strategic input for production optimization activities, remedial jobs, workovers, well test interpretations, permeability estimations, and 3D dynamic reservoir modeling.