Schlumberger Technology Corporation

Ramachandra Ganesh Shenoy

Sandip Bose

Bikash Kumar Sinha

Henri-Pierre Valero

Thomas J Plona

Michael Kane

Methods for downhole waveform tracking and sonic labeling employ &ldquo;tracking algorithms&rdquo; and Bayesian analysis to classify STC waveforms. More particularly, according to the tracking part of the invention, a probability model is built to distinguish true &ldquo;arrivals&rdquo; (e.g. compressional, shear, etc.) from &ldquo;false alarms&rdquo; (e.g. noise) before the arrivals are classified. The probability model maps the &ldquo;continuity&rdquo; of tracks (slowness/time over depth) and is used to determine whether sequences of measurements are sufficiently &ldquo;continuous&rdquo; to be classified as tracks. The probability model is used to evaluate the likelihood of the data in various possible classifications (hypotheses). Prior and posterior probabilities are constructed for each track using the tracking algorithm. The posterior probabilities are computed sequentially and recursively, updating the probabilities after each measurement frame at depth k is acquired. The classification part of the invention determines the hypotheses with the maximum &ldquo;posterior probability&rdquo; according to Bayes' Theorem.

Methods for downhole waveform tracking and sonic labeling

A method for determining properties of an earth formation surrounding an earth borehole that involves: providing a logging device moveable through the borehole; transmitting sonic energy into the formation; receiving sonic energy that has traveled through the formation; producing signals representative of the received sonic energy; determining whether the formation is anisotropic; determining whether the formation is inhomogeneous; and outputting a characterization of the formation as one of the following types: isotropic/homogeneous, anisotropic/homogeneous, isotropic/inhomogeneous, and anisotropic/inhomogeneous.

Sonic well logging for characterizing earth formations

A method for determining alteration of a region of an earth formation surrounding an earth borehole, comprising the steps of providing a logging device that is moveable through the borehole; transmitting sonic energy into the formation and receiving, at a plurality of transmitter-to-receiver spacings, sonic energy that has traveled through the formation, and producing signals representative of the received sonic energy for the plurality of transmitter-to-receiver spacings; determining sonic transit times and differential transit times for the respective transmitter-to-receiver spacings; deriving a test statistic from the differential transit times; and determining the presence of alteration of a region of the formations from the test statistic. An associated apparatus for carrying out the method is also described.

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Paris, France

Ramachandra Ganesh Shenoy