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Measuring Cross Section of the Borehole Cracks Using N Sector Density Measurement

IP.com Disclosure Number: IPCOM000126791D
Publication Date: 2005-Aug-01
Document File: 1 page(s) / 12K

Publishing Venue

The IP.com Prior Art Database

Abstract

Abstract of the Invention: It is a raw idea that needs to be tested and expanded upon by someone but sounds promising to me in line with Borehole Stability talk 2 weeks ago. We discussed it briefly with Gamal and thought that it is impossible to try to measure cracks that are of size smaller that the size of the bin, because resolution would not allow. However it is not resolution that counts when you want to measure the LATER CROSS SECTION of the cracks: If image is represented as a single time series, it is composed of discrete cycle waves – multiples of fundamental frequency corresponding to one full rotation + NOISE. It is the signal that has discrete angular frequency spectrum. DC component (0 frequency) is always the greatest. Bed boundaries, and elliptic boreholes or tool offset from center are low amplitude harmonic waves. The higher the frequency, the lower the magnitude of the waves. When the deep crack appears in the borehole it is a situation of unusually large contrast of density and the short space detector will develop unusually large amplitudes of cycle waves at frequencies multiples of fundamental (one full rotation). Yes the Signal to noise ratio is normally poor at higher frequency, BUT now we have a lot bigger signal due to cracks (low mud density). That signal is a function of LATERAL cross section area for ALL cracks present in the borehole! These should be coincident at both LS and SS detector. Integrated amplitude of harmonics above normal background is a measure of borehole cracks. Formation density could be derived as DC component of the compensated density and then plugged into SS detector response to relate the high frequency signal with CROSS SECTION of borehole cracks.

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Abstract of the Invention:

It is a raw idea that needs to be tested and expanded upon by someone but sounds promising to me in line with Borehole Stability talk 2 weeks ago. We discussed it briefly with Gamal and thought that it is impossible to try to measure cracks that are of size smaller that the size of the bin, because resolution would not allow. However it is not resolution that counts when you want to measure the LATER CROSS SECTION of the cracks: If image is represented as a single time series, it is composed of discrete cycle waves – multiples of fundamental frequency corresponding to one full rotation + NOISE. It is the signal that has discrete angular frequency spectrum. DC component (0 frequency) is always the greatest. Bed boundaries, and elliptic boreholes or tool offset from center are low amplitude harmonic waves. The higher the frequency, the lower the magnitude of the waves. When the deep crack appears in the borehole it is a situation of unusually large contrast of density and the short space detector will develop unusually large amplitudes of cycle waves at frequencies multiples of fundamental (one full rotation). Yes the Signal to noise ratio is normally poor at higher frequency, BUT now we have a lot bigger signal due to cracks (low mud density). That signal is a function of LATERAL cross section area for ALL cracks present in the borehole! These should be coincident at both LS and SS detector. Integrated amplitude of harmonics above normal backgroun...