Time-variable gain for correction of fluid attenuation in downhole acoustic tools

摘要

An apparatus for use in a wellbore is provided that in one embodiment may include at least one transmitter configured to generate acoustic signals in the wellbore, at least one receiver configured to receive acoustic signals from a formation surrounding the wellbore in response to the transmitted acoustic signal and also configured to provide electrical signals representative of the received acoustic signals, a circuit configured to apply a time-variable gain to the electrical signals to amplify the electrical signals, and a processor configured to process the amplified electrical signals and provide a property of interest.

主权项

1. A method of estimating a property of interest relating to a formation surrounding a wellbore, comprising:
determining a first gain value and a second gain value of a time-variable gain from attenuation of acoustic signals in a selected fluid and a timing for ramping between the first gain value and the second gain value from a velocity of the acoustic signals in the selected fluid; generating an acoustic signal in the wellbore having the selected fluid; generating an electrical signal representative of a received acoustic signal received by a sensor from the formation responsive to the generated acoustic signal; applying the determined time-variable gain to the generated electrical signal to amplify the electrical signal to compensate for the attenuation of the acoustic signal when traveling through the selected fluid, wherein the time-variable gain is ramped between the first gain value and the second gain value such that the time-variable gain reaches the second gain value at a time when the generated electrical signal exhibits a peak value; and processing the amplified signals to estimate the property of interest.