R.W. Streeter
Computalog Wireline Services
R.L. Allen
Mobil New Producing Ventures
ABSTRACT
The responses of the 6FF40 deep induction in thin, resistive beds are significantly improved through the use of derivatives applied to the deconvolved deep induction signal. The resultant, enhanced measurement has sharper, more accurate bed boundaries and a value for Rt that is significantly improved in beds as thin as 1 foot (.3 meters).
This technique was developed through extensive forward modeling of deep induction responses to various beds of known resistivity and thickness. Derivatives of the ILD were then used in the inversion to duplicate as closely as possible the original “true” responses. Explicit in the technique is a systematic noise detection and reduction routine that is effective against the relatively minuscule induction noise level without degrading bed boundary responses.
Differential processing has several advantages over current techniques: 1. Speed -typically 1-2 minutes on a PC per 1,000 feet of data are required for processing, 2. Only the 6FF40 curve is required for bed boundary detection and processing, 3. Most 6FF40 type measurements are usable, and 4. Processing can be applied to “old” induction logs by digitizing the deep induction curve over the zones of interest, removing obsolete corrections, and applying the processing technique.
The technique is applicable to induction log measurements of low to medium resistivities, with particular emphasis in interbedded shaly sands sequences.
The methodology is explained, and the results of modeling and examples of field data shown.