SONIC LOGGING FOR ASSESSING WELL INTEGRITY

摘要

Methods are disclosed for detecting fluid in at least one annulus around at least one casing installed in a borehole traversing a formation utilizing a sonic tool. The sonic tool is activated in the borehole and the received sonic waveforms are processed to obtain a dispersion plot. A reference dispersion plot is generated using a model of the borehole where the casing is well-bonded by cement. The obtained and reference dispersion plots are compared. An indication of fluid and in some cases, the specific radial location thereof is obtained based on the signature of the obtained plot as opposed to the reference plot. The methods are effective in doubly-cased boreholes using monopole and/or dipole sources.

主权项

1. A method for detecting fluid in at least one annulus around at least one casing installed in a borehole traversing a formation, said at least one casing, said at least one annulus, said borehole and said formation having a configuration, said method comprising:
a) locating a sonic tool with a plurality of spaced receivers and at least one of a monopole sonic source and a dipole sonic source at a location in the borehole; b) activating said sonic tool such that sonic waveforms are recorded by said plurality of spaced receivers; c) processing said sonic waveforms to obtain a first dispersion plot that plots slowness as a function of frequency; d) generating a reference dispersion plot that plots slowness as a function of frequency for said configuration by using a modeling tool and assuming that said at least one annulus contains cement that is well-bonded to said at least one casing; e) comparing said first dispersion plot to said reference dispersion plot and identifying an indication of fluid in at least one of said at least one annulus at the location by locating differences between said first dispersion plot and said reference dispersion plot.