Schlumberger Technology Corporation

Zlatko Sijercic

Thomas D Barber

Gerald N Minerbo

Tracy E Broussard

The present invention is directed to a method for removing periodic errors from well log data. The method comprises defining a parametric model of well log data to identify periodic errors due to the borehole environment are present, and removing the periodic errors from the well log data.

Parametric modeling of well log data to remove periodic errors

The present invention relates generally to a method and apparatus for evaluating the resistivity of invaded formations at high apparent dip angle. A multi-array induction tool having a plurality of arrays is disposed in a borehole. Signals from a subset of coils of the array are selected to probe different volumes of the formation surrounding the borehole. The maximum entropy method is used to process data from the subset of coils to effectively remove distortions produced by shoulder and dip effect in the presence of shallow, moderate, or deep invasion. An advantage of the invention is a computer program that accurately predicts the response of induction arrays in an assumed layered formation with dip. After processing the data, the resulting multi-array induction log will indicate a conductivity profile for the subset of coils which is substantially identical to that of an array in a thick bed, without dip or layering, with the same invasion profile. A 1D radial inversion of the resulting logs at each point in depth will give a closer estimate of the actual formation parameters, R.sub.xo, R.sub.t, and the invasion radius.

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Houston, TX, United States of America

Zlatko Sijercic